NDLI: Aerodynamic Drag on Vehicles in Tunnels

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Gouse, S. William Noyes, B. S. Swarden, M. C. Nwude, J. K.
Copyright Year	1969
Abstract	The purpose of this study was to investigate the aerodynamic drag on vehicles moving in guideways of varying degrees of enclosure. The reason for this study was that several potential high speed ground transport system concepts involve high speed motion of vehicles in enclosed guideways for significant portions of their travel time. Analytical and experimental investigations have been carried out. The analytical studies developed the solution for the aerodynamic drag on a vehicle in an enclosed guideway in laminar flow. The analysis is based on an analogy between the governing equations for the unsteady flow resulting when an infinite body is started impulsively from rest and the steady flow that results from steady motion of a semi-infinite body. The results of this analysis for laminar flow provided a base from which to begin in turbulent flow and were used to justify the basing of a drag coefficient on the wetted surface area of a vehicle rather than the frontal area of a vehicle. Preliminary experiments were executed using spheres as vehicle models. Final experimental studies were carried out using cylindrical models in circular tunnels of various lengths and various degrees of wall porosity. A drop testing apparatus was employed and results were obtained for Reynolds number of the order of 5 · 105 . Results to date indicate that for vehicle length-diameter ratios of the order of 15 and above, with tunnel to vehicle diameter ratios of 1.5 and greater, a drag coefficient based on the wetted surface area of the vehicle is independent of the vehicle length-diameter ratio for incompressible flow. Results also indicate that, for incompressible flow, employing a tunnel model with a closed end simulates a tunnel length-diameter ratio of infinity. Tunnel wall porosity, assuming relatively unobstructed motion of fluid outside the porous wall, has a marked effect on decreasing the aerodynamic drag on vehicles moving in enclosed guideways and that for the range of variables investigated (clearance ratio as low as 1.4) tunnel wall porosity of 20 per cent is adequate for all the significant drag reduction that is possible. Qualitative predictions of loss coefficient analytical modeling and literature on transonic flow wind tunnel testing with porous walls are in agreement with the data presented.
Starting Page	694
Ending Page	706
Page Count	13
File Format	PDF
ISSN	00982202
e-ISSN	1528901X
Journal	Journal of Fluids Engineering
Volume Number	91
Issue Number	4
DOI	10.1115/1.3571210
Language	English
Publisher	The American Society of Mechanical Engineers
Publisher Date	1969-12-01
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Clearances (Engineering) Drag (Fluid dynamics) Drag reduction Drops Equations Flow (Dynamics) Fluids Laminar flow Modeling Motion Porosity Reynolds number Testing Transonic flow Tunnels Turbulence Unsteady flow Vehicles Wind tunnels
Content Type	Text
Resource Type	Article
Subject	Mechanical Engineering

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