Fluids

Research

11 pages, 14090 KiB

Open AccessArticle

Aerodynamic Drag Reduction of Railroad Tank Wagons

by Christian Navid Nayeri, Jonathan Tschepe, Harald Schulze and Hanno Schell

Fluids 2022, 7(8), 283; https://doi.org/10.3390/fluids7080283 - 19 Aug 2022

Viewed by 2345

Several geometrical modifications for passive flow control applied to a railroad tank wagon were investigated for the purpose of assessing the potential for the aerodynamic optimization of freight trains. The modifications were designed in accordance with applicable requirements and regulations. Four different modifications [...] Read more.

Several geometrical modifications for passive flow control applied to a railroad tank wagon were investigated for the purpose of assessing the potential for the aerodynamic optimization of freight trains. The modifications were designed in accordance with applicable requirements and regulations. Four different modifications were investigated in the wind tunnel of the TU Berlin with 1:25 scaled wagon models: face radius, side skirts, fairing of the roof platform, and the newly introduced inter-wagon discs. In order to simulate the positions of the tested wagon at the end of a long train, the boundary layer on the train model setup was artificially thickened by spires. The Reynolds number was in the range of 0.4 ×

10^{6}

. The results of the experiments show that the proposed measures can reduce the aerodynamic drag of the individual wagon by up to 29%, depending on the location in the train consist. It was also shown that by combining different measures, the individual drag reductions add up. The device with the highest drag reduction was found to be the inter-wagon disc. Three different diameters of the inter-wagon disc were investigated. The largest diameter performed best and was less sensitive to the moving direction of the wagon in comparison to the smaller diameters. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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18 pages, 12223 KiB

Open AccessArticle

POD-Based Model-Order Reduction for Discontinuous Parameters

by Niklas Karcher

Fluids 2022, 7(7), 242; https://doi.org/10.3390/fluids7070242 - 14 Jul 2022

Cited by 1 | Viewed by 2507

Abstract

Reduced-order models (ROMs) based on proper orthogonal decomposition (POD) are widely used in industry. Due to the rigid requirements on the input data, these methods struggle with discontinuous parameters, e.g., optional rear spoiler on a car. In order to also include these types [...] Read more.

Reduced-order models (ROMs) based on proper orthogonal decomposition (POD) are widely used in industry. Due to the rigid requirements on the input data, these methods struggle with discontinuous parameters, e.g., optional rear spoiler on a car. In order to also include these types of parameters, a new method is presented that splits the full-order model (FOM) domain with its discontinuous parameters into multiple ROM subdomains. The resulting subdomains then again comply with the ROM requirements, and the established and proven ROM methods can be applied. The steps involved in computing a ROM based on the proposed method, by setting up the subdomains, mapping the FOM data into the domains, as well as computing the ROMs on the domains, are shown in detail in this paper. The method is employed on two use cases. The academic one-dimensional use case focuses on how the steps involved are employed and analyzes the introduced errors. The second use case’s FOM is based on the DrivAer body with an optional rear spoiler computed using computational fluid dynamics (CFD) and demonstrates the usage in an industrial environment. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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14 pages, 4578 KiB

Open AccessArticle

Aerodynamics of High-Speed Trains with Respect to Ground Simulation

by Dennis Weidner, Daniel Stoll, Timo Kuthada and Andreas Wagner

Fluids 2022, 7(7), 228; https://doi.org/10.3390/fluids7070228 - 5 Jul 2022

Cited by 2 | Viewed by 3364

Abstract

Wind tunnel testing is commonly used to assess and optimize the aerodynamic characteristics of high-speed trains. The train model is usually mounted above a static ground plane, but a moving ground is necessary for the correct representation of the relative motion between train [...] Read more.

Wind tunnel testing is commonly used to assess and optimize the aerodynamic characteristics of high-speed trains. The train model is usually mounted above a static ground plane, but a moving ground is necessary for the correct representation of the relative motion between train and ground. This study focuses on the effect of the applied ground simulation on the aerodynamics of a high-speed train. Wind tunnel tests using a stationary and a moving ground were carried out using a 1:20 scale model of a high-speed train’s first car. Numerical simulations for two moving ground configurations are created, and the simulation setup is validated using surface pressure measurements from the wind tunnel tests. It is shown that the ground simulation has a significant effect on the drag in the considered yaw angle range. Additionally, the change in drag due to bogie fairings is evaluated and an impact of the applied ground simulation on the drag reduction is observed. The drag reduction of front and rear bogie fairings is valued similarly using a static ground, however on a moving ground the drag reduction of front bogie fairings is significantly increased. Good agreement between simulations and experiments is achieved. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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15 pages, 9163 KiB

Open AccessArticle

Aerodynamic Optimization of a Reduced Scale Model of a Ground Vehicle with a Shape Morphing Technique

by Ceyhan Erdem, Yoann Eulalie, Philippe Gilotte, Stefan Harries and Christian N. Nayeri

Fluids 2022, 7(5), 166; https://doi.org/10.3390/fluids7050166 - 10 May 2022

Cited by 4 | Viewed by 3349

Abstract

Aerodynamic performances of ground vehicle continuously improve and a lot of both wind tunnel measurements and Computational Fluid Dynamics (CFD) investigations contribute in the identification of local zones where shape deformation can lead to drag force reduction. Gradient-based optimization with optimal system involving [...] Read more.

Aerodynamic performances of ground vehicle continuously improve and a lot of both wind tunnel measurements and Computational Fluid Dynamics (CFD) investigations contribute in the identification of local zones where shape deformation can lead to drag force reduction. Gradient-based optimization with optimal system involving CFD models is one of the powerful methods for shape optimization, but a genetic algorithm applied on the surrogate model can also explore a large design space in a reasonable period of computation time. In this paper, we present an aerodynamic optimization technique using a Kriging model in order to perform CFD simulations of different front air dam geometries situated below the front bumper of a reduced scale road vehicle. A first design-of-experiment (DoE) is undertaken with Large Eddy Simulations (LES), involving height geometric parameters for radial-basis-function of the front air dam, utilizing a Sobol algorithm. Then, a multi-objective-genetic-algorithm (MOGA) is applied on the constituted surrogate model, depending on the geometric parameters of the front air dam, in order to reach a minimum drag coefficient value by considering pressure constraints. Results show that a front air dam can increase the pressure at the rear of the tailgate, especially by slowing the airflow below the underfloor, but an optimum balance is necessary in order to not increase the stagnation pressure on the air dam, leading to the loss of this benefit. The Sobol technique driven by the Kriging model enables the retrieval of optimum airdam shapes found with wind tunnel tests, even with relatively coarse numerical meshes used for CFD simulations. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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14 pages, 29505 KiB

Open AccessArticle

On the Prediction of Boundary Layer Quantities at High Reynolds Numbers

by Jonathan Tschepe

Fluids 2022, 7(3), 114; https://doi.org/10.3390/fluids7030114 - 17 Mar 2022

Cited by 3 | Viewed by 2319

Abstract

In the current paper, a new formula for calculating boundary layer quantities—such as the boundary layer thickness, friction coefficients, and the boundary layer profile—for a flat plate is presented. The formula is based on the power-law approach and represents a generalisation of the [...] Read more.

In the current paper, a new formula for calculating boundary layer quantities—such as the boundary layer thickness, friction coefficients, and the boundary layer profile—for a flat plate is presented. The formula is based on the power-law approach and represents a generalisation of the 1/7 power-law to a more extensive Reynolds number range. In addition to the derivation and the theoretical background, the main focus is on the comparison with various experimental data from the literature. The good agreement of the data shows that this approach allows for precise predictions of boundary layer quantities for a flat plate with zero-pressure gradients. Especially for estimating boundary layers along with large vehicles such as trains, ships, or aeroplanes, the formula offers added value in terms of accuracy compared to previously existing approaches, such as the 1/7 power-law. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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16 pages, 8530 KiB

Open AccessArticle

Extension of Spectral/hp Element Methods towards Robust Large-Eddy Simulation of Industrial Automotive Geometries

by Walid Hambli, James Slaughter, Filipe Fabian Buscariolo and Spencer Sherwin

Fluids 2022, 7(3), 106; https://doi.org/10.3390/fluids7030106 - 14 Mar 2022

Cited by 2 | Viewed by 2986

Abstract

A spectral/hp element methodology is utilised to investigate the SAE Notchback geometry with 20

^{\circ}

backlight and 3

^{\circ}

diffuser at

R e = 2.3 \times 10^{6}

. The study presented here considered two different mesh approaches: one focusing on classical h-type [...] Read more.

A spectral/hp element methodology is utilised to investigate the SAE Notchback geometry with 20

^{\circ}

backlight and 3

^{\circ}

diffuser at

R e = 2.3 \times 10^{6}

. The study presented here considered two different mesh approaches: one focusing on classical h-type refinement with standard solution polynomial order (HFP3) and a second case considering relatively coarse mesh combined with high solution polynomial order (HCP5). For the same targeted number of degrees of freedom in both meshes, the results show significant differences in vorticity, flow structures and surface pressure. The first guidelines for hp refinement strategy are deduced for complex industrial cases. Further work on investigating the requirements for these hybrid techniques is required in order to maximize the benefits of the solution and mesh refinements in spectral/hp element method simulations. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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13 pages, 2081 KiB

Open AccessArticle

Reducing Slipstream Velocities Experienced in Proximity to High-Speed Trains

by Jordan Ashley Dunlop and Mark Christopher Thompson

Fluids 2022, 7(2), 72; https://doi.org/10.3390/fluids7020072 - 9 Feb 2022

Cited by 1 | Viewed by 1969

Abstract

Slipstream wake structures generated by the passing of high-speed rail vehicles represent a hazard to passengers and workers in close proximity. In this article, the possibility of reducing peak slipstream velocities through the implementation of angled fins or swirling flow injection is assessed [...] Read more.

Slipstream wake structures generated by the passing of high-speed rail vehicles represent a hazard to passengers and workers in close proximity. In this article, the possibility of reducing peak slipstream velocities through the implementation of angled fins or swirling flow injection is assessed on the basis of improved delayed detached eddy simulations (IDDES). The key to improving slipstream velocities involves redirecting and/or reducing the internal energy, a pair of meandering counter-rotating vortex cores that are associated with large wake slipstream deviations. It is demonstrated that the danger imposed by slipstream wake structures, as measured by the induced velocity measures recorded at a series of test points adjacent to the passing train, could be significantly reduced, with decreases from 10% up to 23%, recorded across a range of sampling locations. The means by which these reductions are generated and the corresponding changes in the flow are also explored through analysis of the modified wakes. As such, these devices show promise at improving the operational safety of high-speed rail vehicles. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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23 pages, 93389 KiB

Open AccessArticle

Numerical Investigation of the Influence of Tire Deformation and Vehicle Ride Height on the Aerodynamics of Passenger Cars

by Francesco Fabio Semeraro and Paolo Schito

Fluids 2022, 7(2), 47; https://doi.org/10.3390/fluids7020047 - 20 Jan 2022

Cited by 6 | Viewed by 6501

Abstract

Wheels and wheel houses contribute up to 25% of the total aerodynamic drag of passenger cars and interact in a complex way with their surroundings. Rims and tires induce complex flow separation mechanisms in a highly unsteady regime and the proximity to the [...] Read more.

Wheels and wheel houses contribute up to 25% of the total aerodynamic drag of passenger cars and interact in a complex way with their surroundings. Rims and tires induce complex flow separation mechanisms in a highly unsteady regime and the proximity to the ground enhances these phenomena. To have a clearer understanding of the flow mechanisms that develop around wheels and inside wheel houses, the effect of tire deformation and vehicle ride height on the aerodynamics of passenger cars has been investigated with unsteady CFD simulations. Tire deformation is modelled with an empirical formulation that provides close-to-real deformed shapes, while vehicle ride height changes are made by applying vertical translations the vehicle body. Slick tire geometries and closed rims have been analysed and their rotation has been modelled with a tangential velocity component applied to their surface. The investigation has been conducted in three steps: different car heights and tire deformation levels have been investigated separately and then combined, classifying the results on the basis of the drag of the vehicle. Results show that even small tire deformation levels can significantly affect the aerodynamic drag, thus deformation should be included in simulations and treated with caution. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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18 pages, 6715 KiB

Open AccessArticle

Effects of Wheel Rotation on Long-Period Wake Dynamics of the DrivAer Fastback Model

by Matthew Aultman, Rodrigo Auza-Gutierrez, Kevin Disotell and Lian Duan

Fluids 2022, 7(1), 19; https://doi.org/10.3390/fluids7010019 - 31 Dec 2021

Cited by 7 | Viewed by 2984

Abstract

Lattice Boltzmann method (LBM) simulations were performed to capture the long-period dynamics within the wake of a realistic DrivAer fastback model with stationary and rotating wheels. The simulations showed that the wake developed as a low-pressure torus regardless of whether the wheels were [...] Read more.

Lattice Boltzmann method (LBM) simulations were performed to capture the long-period dynamics within the wake of a realistic DrivAer fastback model with stationary and rotating wheels. The simulations showed that the wake developed as a low-pressure torus regardless of whether the wheels were rotating. This torus shrank in size on the base in the case of rotating wheels, leading to a reduction in the low-pressure footprint on the base, and consequently a

7 %

decrease in the total vehicle drag in comparison to the stationary wheels case. Furthermore, the lateral vortex shedding experienced a long-period switching associated with the bi-stability in both the stationary and rotating wheels cases. This bi-stability contributed to low-frequency side force oscillations (<1 Hz) in alignment with the peak motion-sickness-inducing frequency (0.2 Hz). Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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16 pages, 32872 KiB

Open AccessArticle

The Influence of the Inter-Relationship of Leg Position and Riding Posture on Cycling Aerodynamics

by Shibo Wang, John Pitman, Christopher Brown, Daniel Tudball Smith, Timothy Crouch, Mark C. Thompson and David Burton

Fluids 2022, 7(1), 18; https://doi.org/10.3390/fluids7010018 - 31 Dec 2021

Cited by 4 | Viewed by 4514

Abstract

Aerodynamics is an important factor affecting cyclist performance, as at the elite level 90% of rider energy is used to overcome aerodynamic drag. As such, much effort has been channeled into understanding the detailed flow around cyclists, since small gains can produce large [...] Read more.

Aerodynamics is an important factor affecting cyclist performance, as at the elite level 90% of rider energy is used to overcome aerodynamic drag. As such, much effort has been channeled into understanding the detailed flow around cyclists, since small gains can produce large rewards. Previous studies have shown that cycling aerodynamic drag is sensitive to leg position during the pedaling cycle; however, a systematic analysis comparing the impact of leg position between different riding postures is yet to be undertaken. To address this question, we compare the impact of leg position for two elite-level riding postures: the standard sprint and pursuit body positions. The comparison shows that the effect of leg position on drag is not consistent between the two riding postures, as the altered flow associated with different leg positions is influenced by the wakes from and proximity of other upstream or nearby components, such as the arms. This study reveals the inter-relationship between leg position and riding posture; and suggests that the flow associated with varied leg position should include surrounding geometrical components to obtain and understand the full aerodynamic impact. Practically, the results are valuable for optimizing the posture and improving skin-suit design for drag minimization. Full article

(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)

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