Browse Topic: Camber
Aerodynamicists around the globe are developing mechanisms and structures inspired by nature that enable variable camber morphing (VCM) for aerodynamic surfaces. The implementation of the VCM mechanism in an airplane wing enhances the performance and stability during various flight segments. The present review article is focused mainly on the up-to-date VCM methods in a qualitative as well as quantitative approach that are specific to Aircraft/unmanned aerial vehicle (UAV) wing configurations. Initial literature discussions are confined to the conventional mechanisms that enable VCM in different aircraft configurations and the added aerodynamic advantages such as lift enhancement, drag reduction, boundary layer separation, and flow control. However, those designs need either external shape optimization or internal structural refinements to ensure the factor of safety (FoS). The modern aviation industry is also focused on bioinspired technology because of the adaptive flying capabilities and stall-delay characteristics. Therefore, a review of bioinspired VCM methods that are assessed based on the aerodynamic potentials is sequentially organized in the article. Additionally, considerations are motivated by the application of various compliant structural patterns for VCM in the aircraft industry. The discussion indicates the prospective benefits of morphing toward the future of the Green Aviation industry.
A multi-objective optimization of a rotor blade airfoil is presented using compressible unsteady Reynolds-averaged Navier-Stokes simulations directly within the optimization loop. The baseline SC1095 airfoil is optimized using NSGA-II with two objectives: pre-stall aerodynamic efficiency representing hover performance, and lift hysteresis loop area representing dynamic stall severity. The optimized airfoil exhibits increased maximum thickness with an aft-shifted crest and substantially higher camber. Static polars show improved lift-to-drag ratio at $Ma = 0.5$ and $0.6$. Hover performance is essentially unchanged relative to the baseline. In forward flight, a progressive power penalty is incurred above $\mu = 0.2$, attributed to higher profile drag at advancing blade Mach numbers. Dynamic stall simulations show an 80% reduction in peak drag and a 50% reduction in peak pitching moment excursion relative to the SC1095, demonstrating the effectiveness of the optimization for retreating blade conditions.
This paper explores novel airfoils for rotorcraft applications using a gradient-free, multi-objective genetic algorithm with 2D URANS simulations. The study considers dynamic kinematics at a Reynolds number of 5Ć105 and a mean Mach number of 0.35. Two optimization scenarios are analyzed: 1) pre-stall kinematics (0Ā° ā¤Ī± ā¤10Ā°) and 2) dynamic stall kinematics (0Ā° ā¤ Ī± ā¤ 20Ā°). The paper compares two objective functions: f1, based on the cycle averaged lift, and Ė f1, which modifies f1 by penalizing hysteresis in the lift coefficient. The effects of uniform vs. fluctuating freestream velocity and reduced frequency on optimal airfoils are also discussed. The proposed optimization approach has resulted in novel airfoil shapes that are characterized by a drooped nose, with a convex surface on the aft upper surface similar to a reflex camber in pre-stall kinematics and less unsteadiness in the air loads for the optimized airfoils under the dynamic stall kinematics.
Smooth camber morphing aircraft offer increased control authority and improved aerodynamic efficiency. Smart material actuators have become a popular driving force for shape changes, capable of adhering to weight and size constraints and allowing for simplicity in mechanical design. University of Michigan, Ann Arbor, MI Uncrewed aerial vehicles (UAVs) are growing in popularity for both civilian and military applications, which makes improving their efficiency and adaptability for various aerial environments an attractive objective. Many studies pursue this goal using morphing techniques that incorporate shape changes not typically seen in traditional aircraft. Due to weight and volume constraints consistent with smaller flight vehicles, smart materials, such as macro fiber composites (MFCs), have been used to achieve the desired shape changes. Macro fiber composites are low-profile piezoelectric actuators which have gained substantial attention within the morphing aircraft community. Piezoelectric actuators operate by generating strain when voltage, and hence an electric field, is applied to the electrodes. Piezoelectric actuators are also well known for their capabilities to produce high force-output and a high-speed actuation response. Unlike traditional piezoelectric actuators, which are composed of solid piezoelectric material, MFCs are manufactured using a series of thin piezoceramic rods in a composite laminate layup allowing them to exhibit excellent flexibility while still maintaining the performance benefits attributed to traditional piezoelectric actuators. Furthermore, MFCs exhibit large out-of-plane curvatures when bonded to a thin inextensible substrate, like steel shim, which shifts the structure's neutral axis. This behavior is attractive for camber morphing airfoil applications and has spurred a large subset of research in the field of morphing aircraft. Though the field of morphing aircraft is brimming with novel morphing mechanisms, camber morphing wings and airfoils have proven to be especially beneficial due to their ability to increase control authority and improve efficiency. MFC actuators have been widely used in camber morphing wings, in part because they are capable of seamlessly generating cambered actuation allowing them to serve both as the airfoil skin and actuator. Furthermore, the lightweight nature of MFCs and their rapid actuation response are advantageous in UAV applications. Reductions in aircraft weight lead to greater fuel efficiency and rapid actuation allows for greater maneuverability. MFC-driven camber morphing has been applied to several UAV control problems including localized optimization for adverse aerodynamic disturbance and stall recovery, as well as improved efficiency and control effectiveness in roll and pitch for a rudderless aircraft. Finally, pitch and yaw control effectiveness and yaw stability were also demonstrated in an avian-inspired rudderless UAV with a camber morphing MFC tail actuator.
The paper investigates the unsteady forces and flowfield of a cycloidal rotor blade undergoing forward flight motion through water tunnel experiments. A particle image velocimetry (PIV) system is used in conjunction with an instrumented blade to measure both the two-dimensional flow velocity around the blade and the fluid dynamic forces. The flow-field studies reveal the formation and shedding of strong leading-edge vortices in both the frontal and rear halves of the circular blade trajectory, which plays a key role in generating lift as observed from the blade force measurements. Increasing forward speed diminishes the size and strength of these leading-edge vortices due to the reduction in angle of attack, which reflects in the blade forces. With pitch kinematics symmetric between frontal and rear halves of the cycle the blade produced significantly higher forces in the rear half compared to the frontal half, which was attributed to the dynamic virtual camber and the differences in relative velocity. The thrust vector was observed to be highly sensitive to both pitch phase offset and spin direction at high advance ratios and required a phase angle around 40-degree for positive propulsive force and lift. At very high advance ratios the blade extracts power from the flow over a large region in the frontal half.
This specification covers established inch/pound manufacturing tolerances applicable to carbon steel sheet, strip, and plate ordered to inch/pound dimensions. These tolerances apply to all conditions unless otherwise noted. The term āexclā is used to apply only to the higher figure of the specified range. Tolerances for product sizes not listed herein shall be as agreed upon by purchaser and vendor.
With an intense competitive automotive environment, it becomes imperative for any OEM to launch their products into the market in a short span of time & with a āFirst Time Rightā approach. Within the current scenario in the Automotive Industry, the selection of optimum set of hard points and wheel geometry often becomes an iterative or a trial-and-error process which is both time consuming and involves higher development cost as there may be instances where 2 to 3 sets of iterations are needed before specification is finalized for production. Through this paper, an attempt has been made to develop a methodology for deciding wheel geometry parameters (covered in the later section of this paper like Caster, Camber, Mechanical trail, etc.) [1, 2, 3, 4] for a three wheeled vehicle as a First Time Right (FTR) approach to cut down on conventional, expensive & time-consuming iterative approach. In this paper, we have studied the parameters which affects the directional stability and steering effort using a multi body dynamics (MBD) model and validated it with a series of experiments on prototype three wheeled vehicles. In a three wheeled vehicle the design of front suspension system is very critical as the steering system or the handle bar is often an integral part attached to the front wheel. The problem definition was approached by carrying out a literature review and identifying the parameters affecting steering effort. Parametric studies were carried out through simulation to understand the effect on handle bar steering effort. The primary objective of this dissertation is to highlight the systematic approach carried out during full vehicle dynamics analysis to identify key wheel geometry hardpoints which influence the steering effort and ride feel for the customer. Similarly, the impact of the above listed parameters can be gauged by the fact that it directly affects the directional stability of the vehicle. The outcome of this study was validated on the actual test vehicle to confirm its universal applicability. Through this paper we have attempted to bring forth new design considerations for a suspension steering linkage geometry in a three-wheeler vehicle which, we feel, will be useful for future reference of similar system architecture.
Passengers would always like to reach their destinations with minimum commute time. Generating a higher thrust is a necessity. This implies that the turbomachinery associated with the power plant has to rotate faster and with higher efficiencies. However, high rotational speeds, mainly in the transonic regime, often lead to boundary layer separation, shocks, compressor stall, and surge. The current investigation is an attempt to reduce the abovementioned phenomena. It involves the performance study of a smoothened controlled diffusion airfoil (CDA) blade that has been optimized by āMulti-Objective Genetic Algorithmā (MOGA) by altering maximum camber location and stagger angle. Inlet pressure is varied from 15 kPa to 30 kPa and the angle of attack ranging from 40.4Ā° to 56.4Ā°. C48-S16-BS1 is validated and considered as the baseline profile, and all other blades are collated to this. It is observed that shifting the location of the maximum camber close to the leading edge and increasing stagger angle result in improvement of blade performance in terms of lower pressure losses for high angles of attack. Shifting the camber location slightly lesser than the mid-chord and increasing the stagger angle showed the best performance throughout. However, moving the camber location close to the trailing edge always resulted in the highest amount of losses due to its poor performance. Furthermore, a higher stagger angle is preferred.
A tire is a prominent part of any vehicle, comprising about 33% of the total aerodynamic drag of a vehicle, and is the only part in contact with the road. In this work, an attempt is made to study the aerodynamic characteristics of a non-pneumatic tire (NPT) with hexagonal spokes (HS) in rotating conditions using SimScaleĀ® computational fluid dynamics (CFD). The effect of various parameters like camber angle, steering angle, and velocity on the aerodynamic performance is evaluated through coefficients of drag and lift. The results are compared with that of the static condition at zero yaw and zero camber to understand the effect of a rotating wheel on aerodynamic performance. Results show that the increase in the camber angle or steering angle results in reduced drag and lift coefficients. At a vehicle velocity of 40 km/h, Cd value has reduced by 24.17%, 19.81%, and 31.33% for a 1.5Ā° camber angle, 15Ā° steering angle, and combined case with 1.5Ā° camber and 15Ā° steering angles, respectively, from the actual value of 0.9098. Also, for a vehicle velocity of 60 km/h, the drag coefficient is reduced by 8.64% from the actual value of 0.98.
ABSTRACT
Wheel rim is one of the most critical safety parts in a vehicle. Strength in cornering loading is one of the most important durability test requirements for automotive steel wheel rim apart from other loading conditions like vertical and impact loads. Based on the category of vehicle and customer usage pattern, the accelerated cornering test is derived for testing steel wheel rims. The simulation and certification of steel wheel rim for the required dynamic durability testing requirement involves many steps ranging from acceptance criteria derivation to reliably addressing known potential failure zones in steel wheel rims. Nave radius and crown are sensitive to cornering loads, given the pitch circle diameter at the concept stage, the known effects of these key parameters are determined from DOE and used as reliable indicators to arrive at the shape and section of the steel wheel rim. Potential failure zones are typically crown and nave radius from weather side (outer) surface and vent hole from the inner surface. Key design elements like coining at vent holes and crown dimensions and their impact on stresses are also discussed. The accelerated cornering test done at a vehicle level is a highly dynamic test which requires careful aggregation of damage history to address it. Deriving the acceptance criteria from mule vehicle is also discussed which requires step-by-step measurement including segregation of strain contributions of bolt torqueing, static wheel reaction, camber effects when vehicle is just grounded and its stabilization on rolling. Data is collected and postprocessed for the cornering test to arrive at robust acceptance criteria for the durability simulation. The reliability of the procedure is ensured by strain correlation between actual test and virtual simulation at the critical locations on the steel wheelrim. This activity for rims has enabled to derive key design guidelines for steel rim to ensure optimum performance within given weight constraints.
Rotor morphing has been investigated in the past for improvement of rotor performance, either for reduction of rotor power demand or for vibratory load alleviation. The present study investigates the application of camber morphing for improvement of rotor performance in hover and vertical flight conditions, with a particular focus on the combination of camber morphing systems and variable RPM rotors. Camber morphing utilizes a smooth flap at the trailing edge of the rotor blade to modify the camber of blade airfoil sections without excessive drag penalties. Two different camber morphing systems will be investigated in this study, namely the active and passive systems. Passive camber morphing, which combines camber morphing with the variable speed rotor concept is the unique aspect of camber morphing which will be the primary focus of this study. The active system can be actuated at frequencies higher than 1/rev of the rotor and requires external power input for functioning. The passive system can be controlled only by varying the RPM of the rotor and requires no additional energy input. Therefore, the passive system is expected to show larger net performance benefits. Variable RPM rotors in themselves show potential towards the reduction of rotor power demand but are largely ineffective for low-speed applications. The combination of camber morphing and the variable speed rotor shows larger performance benefits than those obtained from the two technologies independent of each other. The two technologies, when combined in passive camber morphing, can remedy each otherās deficiencies and improve the overall rotor performance. The use of camber morphing shows more benefit for operating points at or near the edge of the flight envelope since the rotor blade sections encounter high average angles of attack for these operating points. Vertical climb and hover at high altitude are examples of flight conditions investigated. Overall, passive camber morphing shows a larger performance benefit as compared to the active system.
The present study proposes and explores a new autonomous morphing concept, whereby an increase in helicopter rotor blade camber of the order of 12-13Ā° is realized over the inboard section of the blade with increase in ambient temperature. The camber change is achieved through a proper integration of Shape Memory Alloys (SMAs) on the lower surface of the blade aft of the leading-edge spar. For a reference rotor (no-SMA) generating 21,000 lbs thrust, operation in hot conditions resulted in a 2,590lb loss in lift. When the SMA camber morphing section extends from the blade root to 50% span, the rotor recovered up to 43% of the lift loss at high temperature. If the camber-morphing section is further extended to 75% span, up to 82% of the lost lift can be recovered.
In order to extend the boundaries of helicopter performance and increase forward-flight speed, it is necessary to reduce the drag on the rotor hub, which can account for as much as 30% of the total parasite drag on the helicopter. Currently, there is limited experimental data available to predict the drag force on new hub configurations. The purpose of this testing is to create a database of lift and drag at various angles of attack to aid in hub design and hub drag prediction. Testing was conducted in the 12 inch-diameter water tunnel at ARL Penn State on four shapes - DBLN 526, 4:1 Ellipse, 3.25:1 Rectangle, and a new Optimized Cambered Shape (OCS) designed at UT Knoxville. Load cell data for lift and drag were obtained for angles of attack from approximately -5 degrees to 5 degrees. Drag data were also calculated using PIV velocity fields. Results are plotted and tabulated for use in future hub drag prediction toolsets.
Aerodynamic shape design of the helicopter tail boom is aimed for anti-torque power requirement alleviation at hover and improvements on sideward flight characteristics. Oval type basic tail boom cross section, whose camber can be modifiable with organic shaped strakes, is proposed to supersede conventional symmetrical tail boom profiles. Performance of several contour shapes is investigated with systematically varying the position and alignment of the strakes through the 2-D RANS simulations. Cross-section shapes that shows highest potential are utilized on tail boom design and to evaluate the resulting hover performance, 3-D CFD analyses are conducted with both of RANS simulations using the actuator disk approach and URANS solutions where blade motions are modeled with overset
A new morphing concept called linearly variable chord-extension was studied for its effectiveness in improving the efficiency of a helicopter rotor. Apart from chord-extension itself, an additional feature which is deflection of the extended part of the chord resulting in an effective camber and additional twist to the airfoil, is also studied for its effect on rotor efficiency improvement. Trim analyses were carried out for various chord-extended rotors for hover as well as various forward flight velocities using DLR's in-house comprehensive analysis code S4. Chord-extension of up to 100 percent and chord-extension-deflection of up to 15 percent were considered. Results show that the linearly variable chord-extension concept is effective in reducing power requirement in both hover and forward flight. Deflection of the extended chord also helps reduce power requirement in hover, especially at higher blade loadings. However, the root torsional moments and hence, the pitch-link loads are seen to increase substantially for the morphed rotors.
A computational investigation was conducted to identify the optimal performance of a rotor with an active camber morphing mechanism using up to twice-per-revolution (2P) control input. Using rotor comprehensive
This paper presents a coupled numerical and experimental study of an unconventional wing profile such as cp-180-050-gn (Cambered plate C = 18% T = 5% R = 0.78). This wing profile deals with low speeds. It is not currently used on any aircraft model. Otherwise, it presents interesting performances that can be exploited for the design of low-speed STOL or VTOL aircraft by mean of the very high lift that it can generate and can fit with different uses such as VAWT, cyclorotors drones, which are designed explicitly for low-speed operations. After a preliminary CFD assessment of the wing a complete experimental characterisation also at high angles of attack has been performed. The excellent agreement between CFD and experiments has allowed producing a complete analysis of the behaviour of the wing profile both before and after stall conditions. This study has the objective of analysing the viability of such an unconventional wing in traditional or over-stalling conditions. A complete modelling of the specific wing is produced with the definition of its potential deployment into unconventional aircraft architectures and both Darreius and Savonius wind turbines.
This paper considers the phenomenon that the self-steer speed when riders bank a motorcycle. This paper points out that this phenomenon originates from capsize mode. Further, it is specified that the first order differential equation representing capsize mode is included in the equation of motion of the steering system. Furthermore, it is specified that this differential equation is the first order differential equation for the roll angle. Therefore, as the roll angle increases, the roll angle further increases and the steering angle also changes, which is the mechanism of capsize mode. Finally, as a result of parameter studies, it is stated that the design parameters that most affect capsize mode were front and rear camber stiffness.
A vehicle drifts due to several reasons from its intended straight path even in the case of no steering input. Vehicle pull is a condition where the driver must apply a constant correction torque to the steering wheel to maintain a straight-line course of the vehicle. This paper presents an investigation study into the characteristics of a vehicle experiencing steering drift. The aim of the work is to study vehicle stability and the causes of vehicle drift/pull during straight line to minimize vehicle pull level and hence optimize safety measures. A wobble in the steering wheel feels like the steering wheel is shaking to the left and right. This may get worse, if speed increases. This paper focuses on modelling and evaluating effects of suspension parameters, differential friction, brake drag variation, Unbalanced mass in the wheel assembly and C.G. location of the vehicle under multibody dynamic simulation environment. Asymmetry of geometry and compliance between left and right side to be causing the drift. The sensitivities of the suspension parameters are presented for each driving condition. In case of acceleration, the interaction of differential friction and driveshaft stiffness and their influence on drift are also studied. For braking condition, suspension parameters such as initial toe, camber and caster variation of front suspension are studied including the braking force difference. The factors influencing steering pull and steering wobble include the compliance properties of the suspension and steering parameters are studied. The mechanics of the brake force interactions with these steering and suspension properties are explained here. Simulation provides an excellent tool to examine and quantify these interactions. The SUV simulation model, MSC.ADAMS/CAR is used to show the importance of linkage compliance as a primary variable and the interactions with other steering and suspension properties. It will be shown that jounce steer and/or brake steer can be used to compensate for the unbalanced effects arising from the linkage asymmetry.
Through Adams/Car software, it was developed a complete template of a double wishbone suspension with a single shock absorber per axle for a formula SAE prototype. With this template it is intended to perform a series of simulations to test its kinematics and dynamics in the situations which the vehicle will be submitted at the competition, then the shock absorberās parameters, double wishbone geometries, camber, caster, toe and kingpin inclination can be improved, validating the system viability and getting a higher performance.
Currently, large companies as well as universities have increased the studies into vehicular dynamic behavior, mainly in order to improve driver and passenger safety. Simulations with complete model vehicle have been used for these studies. The tire is one of the most important vehicular component as the only connection with the ground and responsible for transmitting all vertical, longitudinal and lateral forces, consequenetly it is the main component on the model vehicle, being crucial for the correlation between computer simulations results and field tests, This paper presents a methodology, development and construction of a device to obtain lateral forces in any combination of toe and camber angles for different conditions of normal load, the tests can be performed on any type of ground, whether dry or wet. The tire datas used as reference were obtained through an experimental test using āFlat Tracā equipment. Based on these data, the components used to measuare the tire force, were developed. After the device construction, bench tests were performed in order to validate all project assumptions and calibrate the device. Finally, the device was installed on a small truck and a verification test were performed.
In this study, we focus on ācamber angle controlā and āderivative steering assistanceā using āsteer-by-wireā as maneuverability and stability improvement techniques that are appropriate for the electric vehicle (EV) era. Movements that produce a negative camber angle generate camber thrust, and vehicle motion performance improvements extend from the fact that the tire side force is increased by the camber thrust effect. In our experimental vehicle, a proportional steering angle system was used to create negative camber angle control via an electromagnetic actuator that allowed us to confirm improvements to both the effectiveness and stability of steering control in restricted cornering areas. More specifically, we determined that it is possible to improve critical cornering performance by executing ground negative camber angle control in proportion to the steering angle. Steer-by-wire refers to an electrical steering technique that allows the steering angle of the entire vehicle to be controlled independently of the front wheel steering angle, thereby providing a high level of steering system control freedom. When derivative steering assistance control is applied, the phase of the front wheel steering angle advances faster in proportion to the steering angle velocity change than would normally occur based on the driverās steering actions, which can improve ease of operation and maneuvering stability. In an experimental vehicle equipped with derivative steering assistance via a steer-by-wire system, the steer effectiveness was improved because the phase of the front wheel steering angle advanced due to the derivative steering assist, thereby improving the vehicle responsiveness.
This paper introduces the Shape Adaptive Blades for Rotorcraft Efficiency (SABRE) Horizon 2020 research program and presents initial comprehensive analysis results on the efficacy of adapting blade shapes as a means of reducing rotorcraft power requirements and emissions. The aims of the research program are introduced, followed by discussion of the six different morphing concepts that will be explored. The morphing mechanisms are based on active camber, chord extension, twist, and active tendon morphing technologies. SABRE will explore the use of these concepts individually and in combination, for rotor quasi-steady configuration-type morphing and up to 2/rev actuation of some of the mechanisms, with the objective being to find the best balance between emissions reductions versus complexity and added weight. Initial investigations into the potential power reductions compared to the baseline full-scale BO-105 main rotor achievable with the morphing concepts were performed using Blade Element Momentum Theory and a comprehensive analysis model that was developed using CAMRAD II. The analytical model was validated by full-scale rotor wind tunnel measurements. A combination of active twist and active chord extension achieved up to 11% performance gain in hover. Active camber morphing performance was very sensitive to the combination of deflection, morphing section radial length and placement on the blade, as well as the actuation phasing and blade loading coefficient. The active camber morphing showed power reductions of up to 5.5% in hover and 5% at an advance ratio of 0.313 with a 2/rev actuation, while the active tendon concept showed the capability to change the dynamic response of the rotor blade.
In this paper, detailed development of a nonlinear aeroelastic coupled trim model of a twin-cyclocopter in forward flight is presented. Twin-cyclocopter consists of two cycloidal rotors as main thrusters and a conventional nose rotor for pitch-torque balance. It is shown that five control inputs (mean and differential rpm, mean and differential phase offset of cyclorotors, rpm of nose rotor) are needed to balance three moments and two forces on cyclocopter in forward flight while forces along lateral direction remain balanced at all stages. In this coupled trim procedure, blade aeroelastic response equations and vehicle trim equations are solved together by simultaneously updating control inputs and blade response. To obtain the blade response and forces for a given set of control inputs, an aeroelastic model of cyclorotor and an aerodynamic model of the conventional nose rotor in forward flight is developed. The nonlinear aeroelastic model of the cyclorotor is developed by coupling unsteady aerodynamic model of cyclorotor in forward flight with a geometrically exact beam based structural framework capable of predicting large bending and torsional deflections of rotor blade. Towards this, complex aerodynamics of the cyclorotor is thoroughly investigated and various underlying phenomena, such as dynamic virtual camber, effects of near and shed wake and leading-edge vortices are rigorously modeled. A modified Double Multiple Streamtube (D-MS) model is implemented to capture the complex dynamic inflow characteristics of cyclorotor in forward flight. The present model is validated with previously published in-house experimental data on the performance of a trimmed cyclorotor at different forward speeds.
This study provides the first in-depth analysis of the formation, strength, and convection of cycloidal rotor tip vortices. The blade force and PIV-based tip-vortex measurements were conducted for different blade aspect ratios and pitch kinematics in water at a chord Reynolds number of 18,000. Two phase-locked PIV configurations were utilized to investigate the flow field induced by the cyclorotor blade: (1) a laboratory-fixed field of view to enable investigation of vortex development at increasing vortex ages, and (2) a blade-fixed field of view to investigate the early development of the wingtip vortex at fixed 2Ā° vortex age for varying azimuthal locations. The instantaneous blade force measurements on the cycloidal rotor showed a decrease in lift coefficient with decreasing blade aspect ratio. This is due to the higher peak swirl velocity of the tip vortex produced by the low AR blade, thereby resulting in higher induced downwash along the blade span. The aspect ratio of the blade did not affect the shape of the vortex convection trajectory, however, the rate of downward convection increased with increasing aspect ratio due to the higher thrust produced. The tip vortices showed self-similarity in both the velocity and the circulation profiles. The measurements indicate that the core-radius of the vortex experiences a logarithmic growth and the swirl velocity experiences a logarithmic decay, with vortex age due to viscous diffusion. When compared to previous helicopter rotor studies, the observed vortex dynamics from the present study exhibit increased viscous diffusion, likely due to the significantly lower Reynolds number. The tip vortex strength varied cyclically with blade azimuthal location due to the cyclic variation of blade pitch angle and the dynamic virtual camber effects. The periodic variation in tip vortex strength leads to a periodic variation in the induced flow velocity on the blade.
This paper describes design optimization of a rotor blade for variable pitch quadrotor unmanned air vehicle (UAV) to ensure optimal performance in hover and forward flight. In order to optimize the blade profile to maximize hover power loading, a modified Blade Element Theory based analysis is developed and validated using experimental measurements for sets of symmetric-untwisted rectangular blade and cambered-twisted variable chord blade. The blade twist and chord distribution is parametrized using fifth order polynomial functions and the BEMT analysis is coupled to Matlab optmization toolbox to maximize the power loading for an operational thrust of approximately 3N. It is observed that use of rotor blade with non-linear twist and non-linear chord variation results in significant improvement in hover performance for the variable pitch quadrotor UAV. The optimized blade profile and chord distribution with GOE-744 airfoil gives approximately 4% higher power loading than the COTS cambered and twisted blade and 17% higher power loading than the untwisted rectangular blade with symmetric airfoil. The forward flight performance of the optimized blades is compared with the baseline blades using a Blade Element Theory and Drees inflow model based trim analysis. It is observed that the optimized blade profile doesn't incur any significant penalty during forward flight due to high twist and its performance is similar to that of untwisted blade.
The present research provides a performance comparison between several low Reynolds number airfoil profiles for the Mars Helicopter. The low density of the Martian atmosphere and the relatively small Mars Helicopter rotor result in very low chord-based Reynolds number flows, Rešø = O(10Ā³ - 10ā“). At low Reynolds numbers, flat and cambered plates can out-perform conventional airfoils, making them of interest for the Mars Helicopter rotor. Performance models are generated for the Mars Helicopter rotor based on a free wake analysis, and the results are compared with Mars Helicopter isolated rotor performance from previous work. A Reynolds-Averaged Navier-Stokes based approach is used to generate the airfoil deck using OVERFLOW. The model is constructed using airfoil data tables (C81 files) that are used by the comprehensive rotor analysis code CAMRADII. Performance results for the Martian atmosphere show improved performance for the cambered plate rotor over conventional airfoils, in terms of thrust for equal power and Figure of Merit for equal blade loading. The cambered flat plate airfoil produces 7% larger maximum rotor thrust versus the Mars Helicopter airfoils, and 5% larger Figure of Merit over the design thrust coefficient range. Larger maximum thrust allows an increase of design blade loading for the same thrust range for control authority, whereas the larger Figure of Merit reduces power requirements.
In this paper, based on our previously preliminary out-of-plane tire model, a complete out-of-plane flexible tire model is further developed by considering the variation of dimension and parameter values among different slices of the tire model. This tire model is validated via various MSC ADAMSĀ® FTire virtual cleat tests. Especially, the cleat tests with non-zero tire camber angles and non-symmetric cleat shapes, which can better capture the out-of-plane tire properties, are included. By comparing the predicted results of the proposed tire model with FTire for various cleat tests, it shows that the complete out-of-plane flexible ring tire model is better at fully representing the actual tire properties for some complicated cleat testing scenarios.
Since the tire inflation pressure has a significant influence on safety, comfort and environmental behavior of a vehicle, the choice of the optimal inflation pressure is always a conflict of aims. The development of a highly dynamic Tire Pressure Control System (TPCS) can reduce the conflict of minimal rolling resistance and maximal traction. To study the influence of the tire inflation pressure on longitudinal tire characteristics under laboratory conditions, an experimental sensitivity analysis is performed using a multivalent usable Corner Module Test Rig (CMTR) developed by the Automotive Engineering Group at Technische UniversitƤt Ilmenau. The test rig is designed to analyze suspension system and tire characteristics on a roller of the recently installed 4 chassis roller dynamometer. Camber angle, toe angle and wheel load can be adjusted continuously. In addition, it is possible to control the temperature of the test environment between ā20 Ā°C and +45 Ā°C. The results of the experimental study that covers a wide range of different wheel loads and inflation pressures for three different tire variations show a significant influence of the inflation pressure on longitudinal tire characteristics as slip stiffness or maximum traction force. To simulate the influence of a TCPS on vehicle dynamics with a numerical simulation tool, it is essential to describe the influence of the inflation pressure on tire characteristics correctly with a tire model. Consequently, the well-known semi-empirical Magic Formula tire model adapted from Pacejka is extended for large inflation pressure changes. The parameters of the tire model are identified with a method of least squares which is implemented in an automatic MATLAB analysis tool. A comparison of the standard and respectively the enhanced tire model show an obvious improvement of the model accuracy.
In order to improve robustness of vehicle dynamic performance, a steering mechanism model is proposed with alignment parameters of front wheel based on preference function method. In the steering mechanism model controllable variables include the trapezoid connection length, the base angle of steering trapezoid, the kingpin inclination angle, caster, camber and uncontrollable variables include load and initial braking velocity. Optimization objective is some vehicle dynamic performance. In the preference function method the individual performance preference and preference aggregation in designing variable space and performance variable space are analyzed. The individual performance preference includes the controllable variable preference, noise factor preference and optimization objective preference. The aggregation function is developed by aggregating all the individual performance preferences. The robustness and optimization results are solved based on mean and variance of aggregation function. The results from the preference function method and Taguchi method have been compared. The data show that the individual performance preferences of the steering mechanism model are significantly improved using the preference function method with the nearly same optimization objective value.
This paper provides a fundamental understanding of the unsteady aerodynamic phenomena on a cycloidal rotor blade operating at ultra-low Reynolds numbers (Reā¼18,000) by utilizing a combination of experimental (force and flowfield measurements) and computational (CFD) studies. For the first time ever, the instantaneous blade fluid dynamic forces on a rotating cyclorotor blade were measured, which, along with PIV-based flowfield measurements revealed the key fluid dynamic mechanisms acting on the blade. A 2D CFD analysis of the cycloidal rotor was developed and systematically validated using both force and flowfield measurements. Studies were performed with both static and dynamic blade pitching. Direct comparison of the static and dynamic pitch experimental results helped isolate the unsteady phenomena (such as dynamic stall, unsteady virtual camber, etc.) from the steady effects. The dynamic blade force coefficients were almost double the static ones clearly indicating the role of unsteady mechanisms on force production on cyclorotor blades. For the dynamic case, the blade lift monotonically increased even up to Ā±45Ā° pitch amplitude due to dynamic stall phenomenon; however, as expected, for the static case, the flow separated from the leading edge after around 15Ā° with large laminar separation bubble (LSB) and eventually completely separating at higher pitch angles. For both static and dynamic pitching cases, there was significant asymmetry in the lift and drag coefficients between positive and negative pitch angles due to the flow curvature effects (virtual camber). CFD flow solution and PIV measured flowfield correlated well and both showed the formation and shedding of strong dynamic stall or leading edge vortices, especially at higher pitch amplitudes, which is the reason for the stall delay and force enhancement. Also, the dynamic stall process during the upper half of the trajectory was significantly different from the lower half even with symmetric blade pitch kinematics because of the reversal of dynamic virtual camber from the upper to the lower half. Even at such low Reynolds numbers the pressure forces, as opposed to viscous forces, were found to be dominant on the cyclorotor blade. The power required for rotation (rather than pitching power) was the domineering component of the total blade power for the dynamic pitching case.
Items per page:
50
1 ā 50 of 216