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A Study of Paradrogue Aerodynamics

Forrest Jack Mobley
  • Technical Paper
  • 2020-01-0027
To be published on 2020-03-10 by SAE International in United States
Scaled paradrogue models were designed, built, and tested for the purpose of possible UAS aerial refueling application. Paradrogue chute gore patterns were changed between three models and studied using wind tunnel testing and computational fluid dynamics simulations. Drag coefficient values, as well as vortex shedding characteristics through POD and DMD analysis, were compared between the three models, with an emphasis on possible affects on flight stability.
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On Shedding Frequency and Aerodynamic Characteristics of a Rotating Wire-wrapped Cylinder

California State University-Long Beach-Hamid R. Rahai
  • Technical Paper
  • 2020-01-0028
To be published on 2020-03-10 by SAE International in United States
Numerical investigations of shedding frequency of rotating smooth and wire-wrapped cylinders, placed in steady flow have been performed. The freestream mean velocity was 10 m/sec. and the smooth cylinder diameter was 5 cm, which corresponds to an approximate Reynolds number based on cylinder’s diameter of 3.2x104. The wire wrapped cylinder had a wire diameter of 5 mm and the ratios of pitch spacing to the cylinder diameter, p/D, was 1.0. The cylinder length to diameter ratio was 20. The rotation rate (λ), the ratio of axial tangential mean velocity at the cylinder’s surface to the free stream mean velocity was 2.0. To obtain the shedding frequency, numerical probes were placed at 3D downstream, 0.5 D above the centerline, spaced at 0.5D along the spanwise direction for obtaining instantaneous axial velocity and shedding frequencies were obtained from spectra of the axial velocity. Results indicate that the lift for the wire-wrapped cylinder is nearly 150% of that of the smooth cylinder, however, it has higher drag force. The lift to drag ratio for the smooth rotating cylinder…
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Performance of Isolated UAV Rotors at Low Reynolds Number

Georgia Institute of Technology-Yashvardhan Tomar, Narayanan Komerath
Indian Institute of Technology-Dhwanil Shukla
  • Technical Paper
  • 2020-01-0046
To be published on 2020-03-10 by SAE International in United States
Vertical takeoff and landing vehicle platforms with many small rotors are gaining importance for small UAVs as well as distributed electric propulsion for larger vehicles. To predict vehicle performance, it must be possible to gauge interaction effects. These rotors operate in the less-known regime of low Reynolds number, with different blade geomety. As a first step, two identical commercial UAV rotors from a flight test program, are studied in isolation, experimentally and computationally. Load measurements were performed in Georgia Tech’s 2.13m x 2.74m wind tunnel. Simulations were done using the RotCFD solver which uses a Navier-Stokes wake computation with low-Reynolds number blade section data. It is found that in hover, small rotors available in the market vary noticeably in performance at low rotor speeds, the data converging at higher RPM and Reynolds number. This may be indicative of the high sensitivity of low-Re rotor flows to minor geometrical differences/imperfections in the rotors. It requires proper handling in computations. CFD results show a higher deviation from the experimental thrust data at low rotor speeds. While thrust…
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Truck Trailer Aerodynamic Design Optimization Through CFD Simulations

GM North America-Leonardo José Della Volpe
Imperial College London / NDF-USP-Filipe Fabian Buscariolo
  • Technical Paper
  • 2019-36-0103
Published 2020-01-13 by SAE International in United States
Cargo trucks are one of the most important and flexible ways of moving cargo within inlands. In some countries, such as Brazil, the economy relies on them to transport all kinds of products, from field and factory to consumer. In order to reduce freight prices, beside route optimization, truck manufactures started to focus on the aerodynamics development of those vehicles, in order to improve the efficiency, reducing fuel consumption and emissions. Although the truck aerodynamics development is important, most vehicles are not manufactured or don’t consider the truck trailer, which plays a key role in the full aerodynamics performance of the truck, once it might increase the front area and also change the overall aero performance.Considering the fact that only few Wind Tunnel facilities in the world are capable of testing a full truck with trailer, the use of Computational Fluid Dynamics (CFD) simulations for the evaluation of the full truck system became the best solution in order to improve the aerodynamic performance of those vehicles. The study here presented proposes the CFD evaluation of…
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Modeling Tire Tread Features

SAE International Journal of Passenger Cars - Mechanical Systems

Chalmers University of Technology, Sweden-Michael D.P. Bolzon
  • Journal Article
  • 06-13-01-0001
Published 2020-01-09 by SAE International in United States
This study details an investigation into the accuracy of a recently proposed tire rotation simulation approach, termed the “MRFg” method. Physical experiments and computational fluid dynamics (CFD) simulations were conducted on a sedan-type passenger vehicle with various tire treads and rims. Furthermore, the effects of the wind tunnel geometry on the method’s accuracy was investigated. The experimental data consisted of drag coefficients, front and rear lift coefficients, base and door surface pressures, and wake surveys at various planes around the wheels. Overall, a comprehensive set of validation data was taken. The CFD simulations were transient, and the geometry closely replicated the experimental geometry, including the tires’ deformations. Generally, the MRFg method predicted the effects of the various tread patterns on the drag coefficient to within four counts. Some outliers occurred. The MRFg method predicted some of the flowfield trends and magnitudes very well, but not others. The inclusion of the wind tunnel geometry significantly increased the accuracy of the methodology.
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Optimization of Race Car Front Splitter Placement Using CFD

Delhi Technological University-Sourajit Bhattacharjee, B.B. Arora, Vishesh Kashyap
  • Technical Paper
  • 2019-01-5097
Published 2019-12-30 by SAE International in United States
The behavior of flow over an automobile’s body has a large effect on vehicle performance, and automobile manufacturers pay close attention to the minimal of the details that affect the performance of the vehicle. An imbalance of downforce between the front and rear portion of the vehicle can lead to significant performance hindrances. Worldwide efforts have been made by leading automobile manufacturers to achieve maximum balanced downforce using aerodynamic elements of vehicle. One such element is the front splitter. This study aims to analyze the aerodynamic performance of automobile at various splitter overhang lengths using Computational Fluid Dynamics (CFD). For the purpose of analysis, a three-dimensional (3D) CFD study was undertaken in ANSYS Fluent using the realizable k-ε turbulence model, based on the 3D compressible Reynolds-Averaged Navier-Stokes (RANS) equations. The National Advisory Committee for Aeronautics (NACA) 4412 was taken as profile for the fixed-length splitter attached to a NASCAR 2019 model body. Vehicle speeds of 200, 250, and 300 km/h were considered in order to simulate the velocity of a race car. Drag coefficient, lift…
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Digital Automotive AC Pulldown Prediction in a Real Driving Condition

Dassault Systemes Simulia-Vijaisri Nagarajan
Dassault Systemes, Simulia Corp-Chin-Wei Chang, Kamalesh Bhambare, Adrien Mann, Edward Tate, Abdelhakim Aissaoui
  • Technical Paper
  • 2019-01-5090
Published 2019-12-30 by SAE International in United States
Automotive Original Equipment Manufacturers (OEMs) are always striving to deliver fast Air-Conditioning (AC) pulldown performance with consistent distribution of cabin temperature to meet customer expectations. The ultimate test is the OEM standard, called “AC Pull Down,” conducted at high ambient temperature and solar load conditions with a prescribed vehicle drive cycle. To determine whether the AC system in the vehicle has the capacity to cool the cabin, throughout the drive cycle test, cabin temperature measurements are evaluated against the vehicle target. If the measured cabin temperatures are equal or lower than the required temperatures, the AC system is deemed conventional for customer usage.In this paper, numerical predictions of the cabin temperatures to replicate the AC pulldown test are presented. The AC pulldown scenario is carried out in a digital Climatic Wind Tunnel simulation. The solution used in this study is based on a coupled approach. With this method, convection is solved using PowerFLOW, a Lattice Boltzmann Method (LBM)-based flow solver, while conduction/radiation are solved using PowerTHERM thermal solver. Cooling loads, reproducing a drive cycle with…
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Evaluation of Cycle Variation of SWACER-like Knocking Using 3D SI Combustion Simulation

Daihatsu Motor Co., Ltd.-Tomonori Kuroki, Yuta Shima, Yasuhisa Ono, Takeshi Serizawa
  • Technical Paper
  • 2019-01-2208
Published 2019-12-19 by SAE International in United States
Cyclic variation on heavy knocking was reproduced using 3D SI combustion simulation with RANS / LES turbulence models and detailed kinetic mechanisms. A 0.66 liter, inline 3 cylinder gasoline engine operated at 1200 rpm, WOT was mainly investigated. It was revealed that the combination of RANS, Liu mech. and calculation over multiple cycles worked well. Detailed process of heavy-knock was also suggested and it was thought that SWACER-like mechanism had concerned. RANS could describe typical behavior of heavy-knock within the first 3 cycle calculation and it showed good agreement with both the actual engine measurement and LES calculation result.
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Stall Mitigation and Lift Enhancement of NACA 0012 with Triangle-Shaped Surface Protrusion at a Reynolds Number of 105

SAE International Journal of Aerospace

University of Petroleum and Energy Studies, India-Aslesha Bodavula, Rajesh Yadav, Ugur Guven
  • Journal Article
  • 01-12-02-0007
Published 2019-11-21 by SAE International in United States
Transient numerical simulations are conducted over a NACA 0012 airfoil with triangular protrusions at a Reynolds number (Re) of 100000 using the γ-Reθ transition Shear Stress Transport (SST) turbulence model. Protrusions of heights 0.5%c, 1%c, and 2%c are placed at one of the three locations, viz, the leading edge (LE), 5%c on the suction surface, and 5%c on the pressure surface, while the angle of attack (AOA) is varied between 0° and 20°. Results obtained from the time-averaged solution of the unsteady Navier-Stokes equation indicate that the smaller protrusion placed at 5%c on the suction surface improves the post-stall lift coefficient by up to 59%, without altering the pre-stall characteristics. The improvement in time-averaged lift coefficients comes with enhanced flow unsteadiness due to vigorous vortex shedding. For a given protrusion height, the vortex shedding frequency decreases as the AOA is increased, while the amplitude of fluctuations in lift coefficient increases as the protrusion height is increased or as the AOA is increased. Nevertheless, mitigation of static stall phenomena is observed for most configurations investigated, and…
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Aerodynamic Analysis of a Passenger Car to Reduce Drag Using Active Grill Shutter and Active Air Dam

ARAI Academy-Raghav Tandon
Automotive Research Association of India-Mohammad Rafiq Agrewale, Kamalkishore Vora
  • Technical Paper
  • 2019-28-2408
Published 2019-11-21 by SAE International in United States
Active aerodynamics can be defined as the concept of reducing drag by making real-time changes to certain devices such that it modifies the airflow around a vehicle. Using such devices also have the added advantages of improving ergonomics and performance along with aesthetics. A significant reduction in fuel consumption can also be seen when using such devices. The objective of this work is to reduce drag acting on a passenger car using the concept of active aerodynamics with grill shutters and air dams. First, analysis has been carried out on a baseline passenger car and further simulated using active grill shutters and air dams for vehicle speed ranging from 60 kmph to 120 kmph, with each active device open from 0° to 90°. The optimized model is then validated for a scaled down prototype in a wind tunnel at 80kmph. Vehicle has been modelled using SolidWorks tool and the simulation has been carried out using ANSYS Fluent. The result shows a significant drag reduction of 12.23% using active grill shutters and air dams.
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