1988-02-01

Some Measurements of the Underbody Flow of a Typical Advanced Ground-Transport Vehicle Model 880247

The aerodynamic characteristics of an Advanced Ground Transport vehicle, Electrodynamic System, have been investigated. A series of wind tunnel tests were undertaken using a 1/13th scale model of 1.423m length and 0.286m width at a speed of 26m/s which produced a Reynolds number per unit length of 1.8*106. This compares with a full-scale Reynolds number of 7.6* 106 per unit length. The overall forces and moments generated by the model were measured using an internal six-component strain gauge balance. Relative ground clearances from 0.4 to 0.011 of model height were tested. The typical operational ground clearance of a vehicle of this type is 0.06 of model height. Extensive surface pressure plotting was also undertaken. Additional flowfield information was obtained using flow visualisation techniques in the wind tunnel
The model was mounted over a moving ground belt which allowed an examination of the effects produced by different ground plane representations, moving and stationary belt. Large changes in the aerodynamic characteristics were produced by changes in ground plane representation when the ground clearance was less than 0.2 model height.
An underbody rake was used to obtain transverse total and static pressure traverses at four longitudinal stations under the model when positioned at zero degrees sideslip. This allowed the underbody flow characteristics to be examined and the drag of the underbody flow was determined using a momentum flux approach. For small gap clearances typical turbulent Couette-flow velocity distributions were observed when the ground belt was moving. Large differences in the value of the underbody ‘flow drag’ were obtained when the ground plane representation was changed. Underbody ‘flow drag’ coefficients of 0.011 and 0.024 were obtained when the model was at h/H = 0.05 for the moving and stationary belt cases respectively.

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