Browse Topic: Turbulence
To address the growing concern of increasing noise levels in urban areas, modern automotive vehicles need improved engineering solutions. The need for automotive vehicles to have a low acoustic signature is further emphasized by local regulatory requirements, such as the EU's regulation 540/2014, which sets sound level limits for commercial vehicles at 82 dB(A). Moreover, external noise can propagate inside the cabin, reducing the overall comfort of the driver, which can have adverse impact on the driving behavior, making it imperative to mitigate the high noise levels. This study explores the phenomenon of change in acoustic behavior of external tonal noise with minor geometrical changes to the A-pillar turning vane (APTV), identified as the source for the tonal noise generation. An incompressible transient approach with one way coupled Acoustics Wave solver was evaluated, for both the baseline and variant geometries. Comparison of CFD results between baseline and variant showed
Electric Vertical Take-Off and Landing (eVTOL) aircraft, conceptualized to be used as air taxis for transporting cargo or passengers, are generally lighter in weight than jet-fueled aircraft, and fly at lower altitudes than commercial aircraft. These differences render them more susceptible to turbulence, leading to the possibility of instabilities such as Dutch-roll oscillations. In traditional fixed-wing aircraft, active mechanisms used to suppress oscillations include control surfaces such as flaps, ailerons, tabs, and rudders, but eVTOL aircraft do not have the control surfaces necessary for suppressing Dutch-roll oscillations.
This study evaluates the effectiveness of two hybrid computational aeroacoustic methods—Lighthill wave model and perturbed convective wave model—in simulating HVAC duct noise in the automotive industry. Using component-level acoustic testing of a Ford HVAC duct, simulations were conducted at varying airflow rates to assess the accuracy of both models in predicting duct noise. The Lighthill wave model, suitable for noise analysis in regions outside turbulent flow areas, showed a good correlation with experimental data, especially in the frequency range of 100 Hz–5000 Hz, but sometimes struggled with pseudo-noise effects at low frequencies near turbulent regions. The perturbed convective wave model, which is suitable for noise analysis anywhere in the flow domain, underpredicted sound pressure levels at low frequencies as well. Both models underpredicted high-frequency noise (>5 kHz) due to insufficient mesh and time-step sizes. Despite these limitations, the Lighthill wave model
In traffic scenarios, the spacing between vehicles plays a key role, as the actions of one vehicle can significantly impact others, particularly with regards to energy conservation. Accordingly, modern vehicles are equipped with inter-vehicle communication systems to maintain specific distances between vehicles. The aerodynamic forces experienced by both leading vehicles (leaders) and following vehicles (followers) are connected to the flow patterns in the wake region of the leaders. Therefore, improving our understanding of the turbulent characteristics associated with vehicles platooning is important. This paper investigates the effects of inter-vehicle distances on the flow structure of two vehicles: a small SUV as the leader and a larger light commercial van as the follower, using a Delayed Detached Eddy Simulation (DDES) CFD technique. The study focuses on three specific inter-vehicle distances: S = 0.28 L, 0.4L, and 0.5L, where S represents the spacing between the two vehicles
The vehicle wake region is of high importance when analyzing the aerodynamic performance of a vehicle. It is characterized by turbulent separated flow and large low-pressure regions that contribute significantly to drag. In some cases, the wake region can oscillate between different modes which can pose an engineering challenge during vehicle development. Vehicles that exhibit bimodal wake behavior need to have their drag values recorded over a sufficient time period to take into account the low frequency shift in drag signal, therefore, simulating such vehicle configurations in CFD could consume substantial CPU hours resulting in an expensive and inefficient vehicle design iterations process. As an alternative approach to running simulations for long periods of time, the impact of adding artificial turbulence to the inlet on wake behavior and its potential impact on reduced runtime for design process is investigated in this study. By adding turbulence to the upstream flow, the wake
The thermoelectric generator system is regarded as an advanced technology for recovering waste heat from automotive exhaust. To address the issue of uneven temperature distribution within the heat exchanger that limits the output performance of the system, this study designs a novel thermoelectric generation system integrated with turbulence enhancers. This configuration aims to enhance convective heat transfer at the rear end of the heat exchanger and improve overall temperature uniformity. A multiphysics coupled model is established to evaluate the impact of the turbulence enhancers on the system's temperature distribution and electrical output, comparing its performance with that of traditional systems. The findings indicate that the integration of turbulence enhancers significantly increases the heat transfer rate and temperature uniformity at the rear end of the heat exchanger. However, it also leads to an increase in exhaust back pressure, which negatively affects system
Researchers at Caltech took an important step toward using reinforcement learning to adaptively learn how turbulent wind can change over time, and then uses that knowledge to control a UAV based on what it is experiencing in real time. California Institute of Technology, Pasadena, CA In nature, flying animals sense coming changes in their surroundings, including the onset of sudden turbulence, and quickly adjust to stay safe. Engineers who design aircraft would like to give their vehicles the same ability to predict incoming disturbances and respond appropriately. Indeed, disasters such as the fatal Singapore Airlines flight this past May in which more than 100 passengers were injured after the plane encountered severe turbulence, could be avoided if aircraft had such automatic sensing and prediction capabilities combined with mechanisms to stabilize the vehicle. Now a team of researchers from Caltech's Center for Autonomous Systems and Technologies (CAST) and NVIDIA has taken an
Researchers have achieved data rates as high as 424Gbit/s across a 53-km turbulent free-space optical link using plasmonic modulators — devices that uses special light waves called surface plasmon polaritons to control and change optical signals. The new research lays the groundwork for high-speed optical communication links that transmit data over open air or space.
In nature, flying animals sense coming changes in their surroundings, including the onset of sudden turbulence, and quickly adjust to stay safe. Engineers who design aircraft would like to give their vehicles the same ability to predict incoming disturbances and respond appropriately. Indeed, disasters such as the fatal Singapore Airlines flight this past May in which more than 100 passengers were injured after the plane encountered severe turbulence, could be avoided if aircraft had such automatic sensing and prediction capabilities combined with mechanisms to stabilize the vehicle.
This study investigates the flow characteristics in the test section of a model-scale, three-quarters open-jet, closed-loop return wind tunnel equipped with a novel device featuring three subsystems to generate transient yaw, gusts, and turbulence. The effect of each subsystem on the resulting turbulent and unsteady flows is evaluated individually and simultaneously. It is demonstrated that this new turbulence generation system can generate yaw distributions with standard deviations ranging from 2.1° to 8.0°. This replicates a wide range of on-road yaw behavior. Additionally, the subsystems can activate transient yaw events and unsteady gusts. Frequency sweeping was demonstrated to fill a wide range of low-frequency spectra, which helps recreate the on-road flow spectra in wind tunnels. Unsteady gusts of more than 15% of the mean flow velocity were achieved. The active turbulence subsystem generates turbulence levels from a few percent, passively, to over 20% intensity levels actively
When traveling in an open-jet wind tunnel, the path of an acoustic wave is affected by the flow causing a shift of source positions in acoustical maps of phased arrays outside the flow. The well-known approach of Amiet attempts to correct for this effect by computing travel times between microphones and map points based on the assumption that the boundary layer of the flow, the so-called shear layer, is infinitely thin and refracts the acoustical ray in a conceptually analogy to optics. However, in reality, the turbulent nature of both the not-so-thin shear layer and the acoustic emission process itself causes an additional smearing of sources in acoustic maps, which in turn causes deconvolution methods based on these maps – the most prominent example being CLEAN-SC – to produce certain ring effects, so-called halos, around sources. In this paper, we intend to cast some light on this effect by describing our path of analyzing/circumventing these halos and how they are linked to the
A structural load estimation methodology was developed for RLV-TD HEX-01 hypersonic experimental mission, the maiden winged body technology demonstrator vehicle of ISRO. Primarily the method evaluates time history of station loads considering effects of vehicle dynamics and structural flexibility. Station loads of critical structures are determined by superposition of quasi-static aerodynamic loads, dynamic inertia loads, control surface loads and propulsion loads based on actual physics of the system, improving upon statistical load combination approaches. The technique characterizes atmospheric regime of flight from vehicle loads perspective and ensures adequate structural margin considering atmospheric variations and system level perturbations. Features to estimate change in loads due to wind variability and atmospheric turbulence are incorporated into the load estimation methodology. Augmentation in loads due to structural flexibility is assessed along the trajectory using vehicle
Patterns of light hold tremendous promise for a large encoding alphabet in optical communications but progress is hindered by their susceptibility to distortion, such as in atmospheric turbulence or in bent optical fiber. Researchers at the University of the Witwatersrand (Wits) have outlined a new optical communication protocol that exploits spatial patterns of light for multi-dimensional encoding in a manner that does not require the patterns to be recognized, thus overcoming the prior limitation of modal distortion in noisy channels.
In order to improve the ignition stability and reduce the cycle-to-cycle variation, it is necessary to understand the mechanism of the flame kernel development and the local quenching effect during the spark ignition process. In this study, experiments for the spark ignition process in a high-speed lean gasoline-air mixture turbulent flow field were conducted. OH* chemiluminescence measurement and focusing Schlieren photography was applied to observe the development of flame kernel and discharge channel behaviors simultaneously. Results indicated that flame kernel fragments, generated by the restrike and short- circuit of discharge channels, quenched due to the local turbulence, which led to slow flame propagation or misfire. In that cases, the initial flame kernels showed stretched behaviors, along with high curvatures.
Lagrangian Particle Tracking (LPT) is a popular flow visualization technique that lets scientists track tracer particles in a three-dimensional volume using highspeed cameras. This method plays an important role in many fluid mechanics studies, particularly those that investigate turbulent flows.
Lagrangian Particle Tracking (LPT) is a popular flow visualization technique that lets scientists track tracer particles in a three-dimensional volume using high-speed cameras. This method plays an important role in many fluid mechanics studies, particularly those that investigate turbulent flows. Pushing the boundaries of this technique, some researchers are beginning to use multiple high-speed cameras driven by sophisticated 3D measurement software which uses temporal information contained in time-resolved data sets to track particles in densely seeded flows. This newer technique, called Shake the Box (STB), predicts the positions of already tracked particles and then corrects errors using image matching. The algorithms triangulate the positions of new particles in the measurement domain, enabling scientists to look at higher-particle densities with greater positional accuracy compared to traditional LPT.
This SAE Aerospace Information Report (AIR) addresses many of the significant issues associated with effects of inlet total-pressure distortion on turbine-engine performance and stability. It provides a review of the development of techniques used to assess engine stability margins in the presence of inlet total-pressure distortion. Specific performance and stability issues that are covered by this document include total-pressure recovery and turbulence effects and steady and dynamic inlet total-pressure distortion.
Traditionally vehicles are designed for wind noise under ideal steady wind conditions. But, passenger comfort is affected by high modulation of cabin noise while cruising in traffic due to variations of instantaneous wind speed and direction from driving through large-scale turbulence. In consequence, designing a vehicle for the best performance in a low-turbulence wind tunnel may lead to issues during on-road conditions. To predict the interior noise corresponding to on-road turbulence, a simulation approach is proposed combining an upstream turbulence flow simulation with an SEA vehicle model. This work is an extension of existing well validated procedures for steady wind conditions. Time-segmented transient loads on panels and steady-state structural acoustics transfer functions are combined, producing interior noise results for a series of overlapping time segments. This interior noise prediction, as a function of time, captures the modulation of wind noise results, which are then
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