Session: 01-07-02 Industrial Fluid Mechanics

Paper Number: 65393

Start Time: August 12th, 10:50 AM

65393 - CFD Analysis and Wind Tunnel Testing of Human Powered Vehicle Drag Coefficients 

The purpose of this study is to determine the effect of vehicle design on drag coefficients. The World Human Powered Speed Challenge (WHPSC) is a competition where cyclists race to break the human powered land speed record, 89.59 MPH. WHPSC is held in Battle Mountain, Nevada on SR 305, which has a section of road specifically prepared for human-powered vehicle racing by the Nevada Department of Transportation. The Sprocket Rocket, a 5-person quad cycle, is one of the Human Powered Vehicles competing in the WHPSC. In 2019 the Sprocket Rocket achieved a top speed of 56.4 MPH, making it the second fastest human powered vehicle with 3 or more riders. In 2021 they will attempt to reach a speed of 63 MPH, by modifying their design, to break a world record. Reducing the drag force on The Sprocket Rocket would allow the power generated by the cyclists to increase velocity instead of overcoming the drag force. This is done by streamlining, altering the geometry of the vehicle to reduce the Drag Coefficient, Cd. Herein, a comparison of CFD to Wind Tunnel test data is presented. Ten different human-powered vehicle designs were examined using a CFD software to find the lowest Drag Coefficient. The results were later verified by a scaled wind tunnel test. The current study reveals that streamlining the nose cone, tail cone, and wheel housing allows for a reduction of drag forces in critical areas, and a reduced drag coefficient. Results provide drag coefficients for the ten different vehicles. This allows for a selection to be made during the design phase, prior to manufacturing. A reduction of drag coefficients in the design phase using CFD software, and a scaled Wind Tunnel test allows for optimization of flow conditions on the vehicle. For the CFD analysis, ANSYS Fluent 2020 R1 Academic Edition was used to complete 18 different CFD cases, which all converged. A PC with the following specifications was utilized; An 8-core/16 thread CPU processor running at 4.1 GHz, 48 Gb of RAM at 3066 MHz and an Nvidia RTX 2080 GPU. The k-e turbulence model with standard wall function treatment is used for the CFD simulations, and the effects of the ground either fixed or moving are considered. Drag coefficient predictions from the CFD range from 0.13 < Cd < 0.28, depending on the type of vehicle considered. Wind Tunnel testing was performed on scale models of the human powered vehicle showing agreement to the CFD results within 15%. The paper will present details of the CFD methodology as well as the wind tunnel testing experimental design and data reduction.

Presenting Author: Kevin Anderson Calif State Polytechnic University

Authors:

Kevin Anderson Calif State Polytechnic University
Tony Estrada Calif. State Polytechnic Univ. at Pomona
Ivan Gundersen Calif. State Polytechnic Univ. at Pomona
Chuck Johnston Calif. State Polytechnic Univ. at Pomona