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CFD and Wind Tunnel Analysis of the Drag on a Human-Powered Vehicle Designed for a Speed Record Attempt

SAE International Journal of Vehicle Dynamics, Stability, and NVH

Cranfield University, UK-Christopher Bennett, Julien Lefieux, Cathal Moloney
NFLC Cranfield University, UK-Nicholas Lawson
  • Journal Article
  • 10-03-02-0008
Published 2019-06-07 by SAE International in United States
A computational fluid dynamics (CFD) and wind tunnel investigation of a human powered vehicle (HPV), designed by the Velo Racing Team at Ostfalia University, is undertaken to analyse the Eco-body’s drag efficiency. Aimed at competing in a high profile HPV speed record competition, the vehicle’s aerodynamic efficiency is shown to compare well with successful recent eco-body designs. Despite several limitations, newly obtained wind tunnel data shows that the corresponding CFD simulations offer an effective tool for analysing and refining the HPV design. It is shown that, in particular, the design of the rear wheel fairings, as well as the ride height of the vehicle, may be optimised further. In addition, refinements to the CFD and wind tunnel methodologies are recommended to help correlation.


Automotive Engineering: May 2019

Dan Carney
  • Magazine Article
  • 19AUTP05_05
Published 2019-05-01 by SAE International in United States

In the downforce vs. turbulence battle, Formula 1 enacts technical changes to rev up the on-track spectacle.

Ongoing aerodynamic development of Formula 1 racecars has the most obvious goals of increasing the cars' downforce and reducing their drag to produce the fastest speeds and quickest lap times.

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Developing a Track Simulation Tool for Formula Student Race Cars Using Python

Ain Shams University-Sherif Khedr, Hashim Elzaabalawy, Mohamed Abdelaziz
Published 2019-04-02 by SAE International in United States
Formula Student is a competition held on yearly basis in multiple countries around the world. Students from different universities participate in this competition implementing some of the most sophisticated techniques in design and analysis of Formula Student car performance. In this research a track simulation tool is developed using Python to analyze the effect of different systems on the car performance, and to test the performance of the car on the Autocross track. For simplicity, the car is modeled as point mass in straight roads and corners. Intensive studies were carried out leading to a conclusion that, in some cases, point mass modeling leads to some inaccuracy and in others it provides the solution. Therefore, to achieve simulation accuracy, the point mass model was replaced with four degrees of freedom, or “bicycle”, model counterpart when it couldn’t provide an accurate solution, and the difference between both models results are discussed. The brake bias ratio selected for the brake system versus human force applied on the brake pedal was optimized and the optimization technique is discussed…
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Evaluation of Ecosystem for Design Assessment and Verification by BAJA Dynamometer Capstone Team at the University of Nebraska

Imagars LLC; Portland State University-Baldur Steingrimsson
Portland State University-Bao Phan, Sung Yi
Published 2019-04-02 by SAE International in United States
This paper summarizes the outcome of an evaluation by capstone design teams from the Department of Mechanical and Materials Engineering at the University of Nebraska-Lincoln, of the Ecosystem for Design Assessment and Verification. The Ecosystem is a design decision support tool whose main goal is to identify design oversights, defined in terms of deviations from the design process or unfulfilled design requirements, early in the design process, guide designers through the design process, and teach proper design techniques. It is capable of automatically assessing students’ design work against ABET compliant learning outcomes. The Ecosystem offers many additional features found useful by capstone design teams, such as automatic generation of formatted project reports as well as interfaces to tools for team communications (Google Drive, Dropbox or OneDrive) or development (e.g., SolidWorks, CATIA, NX Unigraphics or AutoCAD).The Ecosystem was recently evaluated by a capstone team working on an automated straw flattening machine and again during a following semester by a team designing a dynamometer used for measuring the engine power of a BAJA race car.The paper draws…
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Increasing the Aerodynamic Performance of a Formula Student Race Car by Means of Active Flow Control

TU Berlin (Technical University)-Ben Steinfurth, Arne Berthold, Steffen Feldhus, Frank Haucke, Julien Weiss
Published 2019-04-02 by SAE International in United States
This article involves an experimental study regarding the capability of fluidic actuators to increase the aerodynamic performance of a four-element race car rear wing. Sweeping jet actuators are integrated in the upper flap, of which the angle of attack is increased by up to ΔαF3 = 40° with reference to a passively optimized setup. Different velocities of the emitted sweeping jets are applied to study the influence of momentum coefficients cμ = 0.04 … 0.98%. To prove the feasibility of the approach, flow control is first applied to a stand-alone rear wing tested in a small wind tunnel. Subsequently, a realistic race car model featuring the controlled rear wing is investigated in a larger-scale wind tunnel. Employing particle image velocimetry, flow visualization techniques as well as pressure and force measurements, we show that the velocity field on the suction side of the upper flap is characterized by flow separation of different degrees when the angle of attack is increased beyond ΔαF3 = 20° (rear wing only) and ΔαF3 = 30° (complete race car). Generally, the employed fluidic devices have a positive impact in terms of…
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A Study of Energy Enhanced Multi-Spark Discharge Ignition in a Constant-Volume Combustion Chamber

Shanghai Jiao Tong Univ-Min Xu
Shanghai Jiao Tong University-Chang ye
Published 2019-04-02 by SAE International in United States
Multi-spark discharge (MSD) ignition is widely used in high-speed internal combustion engines such as racing cars, motorcycles and outboard motors in attempts to achieve multiple sparks during each ignition. In contrast to transistor coil ignition (TCI) system, MSD system can be greatly shortened the charging time in a very short time. However, when the engine speed becomes higher, the ignition will be faster, electrical energy stored in the ignition system will certainly become less, especially for MSD system. Once the energy released into the spark plug gap can’t be guaranteed sufficiently, ignition will become more difficult, and it will get worse in some harsh environment such as strong turbulence or lean fuel conditions. With these circumstances, the risks of misfire and partial combustion will increase, which can deteriorate the power outputs and exhaust emissions of internal combustion engine. Therefore, in order to extend the ignitability limit and reduce the combustion variation without sacrificing spark energy for high speed engines, an energy enhanced multi-spark discharge (EEMSD) ignition system is developed in this study. The principle of…
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Improving the Michigan Tech Formula SAE Design Process

CADENAS PARTsolutions, LLC-Timothy Thomas
Michigan Technological University-James De Clerck, Austin Arenz
Published 2019-04-02 by SAE International in United States
Michigan Tech Formula SAE is a student-led team that designs and builds an open-wheel race car to compete with similar teams from other universities in early May each year. The team has adopted a vehicle development process where the design, build, and test/compete phases happen in consecutive years. This process is motivated by the need to perform validation testing in the fall prior to competition due to Houghton winters lingering well into April. In order to compete every year, all three phases are always in-process to ensure the consecutive completion vehicles.As a student organization, Formula SAE membership has a two to three year turnover rate. This limited organizational memory results in redesign rather than re-use of parts. Simple parts are easier to re-model than manually search a directory structure for an existing design. This redundant work is wasted effort and is often results in repeating poor design features that had been improved by previous team members.Michigan Tech Formula SAE is working with CADENAS PARTsolutions to deploy an “Authoritative Source” of supplier and standard parts in…
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Numerical Analysis of Underbody Diffusers with Different Angles and Channels

CATARC-Xuelong Liu, Qinglu Chen
Jilin University-Jie Tian, Yingchao Zhang
Published 2019-04-02 by SAE International in United States
The underbody diffusers are used widely in race cars to improve the flow field structure at the bottom of the car and provide enough downforce. In recent years, passenger cars have begun to use bottom diffuser to improve aerodynamic characteristics, so as to reduce drag and increase downforce. In this paper, the aerodynamic characteristics of the bus with different underbody diffuser angles and channel numbers are studied by numerical simulation analysis. Firstly, the aerodynamics of the bus under different diffuser inlet and outlet angles are studied, and then an optimal inlet and outlet angle is determined based on the simulation results. Then, using this angle as a constant, the 2, 3, and 4 channel numbers were chosen as the diffuser channel variables to study the influence of the multiple-channel diffusers on the aerodynamic drag of the vehicle. The results of the study show that reasonable diffuser inlet and outlet angles can improve the bottom pressure distribution and wake structure of the bus, resulting in a maximum increase in downforce of 38.2%. In addition, under a…
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Fine Tuning the SST k − ω Turbulence Model Closure Coefficients for Improved NASCAR Cup Racecar Aerodynamic Predictions

University of North Carolina-Chen Fu, Charles Bounds, Mesbah Uddin, Christian Selent
Published 2019-04-02 by SAE International in United States
Faster turn-around times and cost-effectiveness make the Reynolds Averaged Navier-Stokes (RANS) simulation approach still a widely utilized tool in racecar aerodynamic development, an industry where a large volume of simulations and short development cycles are constantly demanded. However, a well-known flaw of the RANS methodology is its inability to properly characterize the separated and wake flow associated with complex automotive geometries using the existing turbulence models. Experience suggests that this limitation cannot be overcome by simply refining the meshing schemes alone. Some earlier researches have shown that the closure coefficients involved in the RANS turbulence modeling transport equations most times influence the simulation prediction results. The current study explores the possibility of improving the performance of the SST k − ω turbulence model, one of the most popular turbulence models in motorsports aerodynamic applications, by re-evaluating the values of certain model closure constants. A detailed full-scale current generation NASCAR Cup racecar was used for the investigation. The simulations were run using a commercial CFD package STAR-CCM+ (version 13.04.010). Five different closure coefficients in the SST k − ω model,…
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Safety and Lateral Dynamics Improvement of a Race Car Using Active Rear Wing Control

University of Ontario Institute of Technology-Mohammed Hammad, Khizar Qureshi, Yuping He
Published 2019-04-02 by SAE International in United States
As the forward speed of a car increases, the safety of the vehicle and the driver becomes a more significant concern. Active aerodynamic control can effectively enhance the lateral stability of high speed vehicles over tight cornering maneuvers. A split rear wing has been proposed. By means of manipulating the attack angles for the right and/or left parts of the split rear wing, a favorable yaw moment may be achieved to ensure the lateral stability of the vehicle. However, active control of the split rear wing has not been adequately explored. This paper proposes a novel active split rear wing, which can improve the lateral stability over tight cornering maneuvers, and will not degrade the longitudinal dynamics of the vehicle. A Linear Quadratic Regulator (LQR) based controller for the active split rear wing is designed using a linear vehicle model. In order to examine the performance of the active split rear wing, Numerical simulation is carried out using the LQR based controller and a yaw-plane vehicle model designed in MATLAB. The effectiveness of the proposed…
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