Search Results

Experimental measurements of a 1:20-scale tractor-trailer configuration were obtained in the 48- by 32-Inch Subsonic Wind Tunnel at NASA Ames Research Center. The model included significant details of the underbody geometries of both the tractor and trailer. In addition, the tractor included a flow-through grill and a simplified engine block to provide an approximation of the flow through the engine compartment. The experiment was conducted at a Reynolds Number of 430,000 for yaw angles between ±14 deg. The measurements included forces and moments and static surface pressures for various underbody configurations. Simple fairings on the underbodies of the tractor and trailer both yielded a reduction in the wind-averaged drag coefficient of 0.018 (2.7%) when tested separately. A horizontal plate designed to block vertical flow in the tractor-trailer gap provided marginally higher drag reduction (0.021, or 3.2%).

A recursive algorithm has been developed to automatically generate multi-grid meshed wind tunnel wake surveys. Using near-real-time processing of 7-hole probe pressure data to obtain velocity components, the local circulation in the flow was computed and used to determine the grid spacing. This results in a significant reduction in the number of sample stations per survey. Results from a recent test at the 7 by 10 Foot Wind Tunnel at NASA /Ames Research Center are presented.

A wind-tunnel test was conducted for an unswept wing with a half-span Fowler flap. Surface pressures, flow visualization, and wake surveys were obtained for two flap riggings representative of landing configurations. The primary influence of the half-span flap is to create spanwise pressure gradients on the main element and flap. Pressure distributions near the flap tip indicate the presence of two distinct suction peaks on the upper surface. Flow visualization using smoke verifies the existence of two co-rotating vortices near the flap tip that merge before reaching the trailing edge. Seven-hole-probe wake surveys yield values for both profile and induced drag.

The effectiveness of an aerodynamic boattail on a tractor/trailer road vehicle was measured in the NASA Ames Research Center 80- by 120- Foot Wind Tunnel. Results are examined for the tractor/trailer with and without the drag reduction device. Pressure measurements and flow visualization show that the aerodynamic boattail traps a vortex or eddy in the corner formed between the device and the rear corner of the trailer. This recirculating flow turns the flow inward as it separates from the edges of the base of the trailer. This modified flow behavior increases the pressure acting over the base area of the truck, thereby reducing the net aerodynamic drag of the vehicle. Drag measurements and pressure distributions in the region of the boattail device are presented for selected configurations. The optimum configuration reduces the overall drag of the tractor/trailer combination by about 10 % at a zero yaw angle.