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Two techniques for advanced flow-simulation in automotive, climatic wind-tunnels have been presented. These are the Slotted-Wall Extension * for improved flow simulation over the test vehicle, and methods for improved thermal boundary-layer simulation. The Slotted-Wall Extension gives a reference q-correction that is relatively independent of vehicle configuration and blockage, prevents the formation of shear layers in the nozzle exit flow, suppresses mean-flow pulsations in the test chamber, and reduces vehicle pressure-simulation errors, with resultant improvement in critical cooling airflows. Measurements over a heated, flat surface show that the open road thermal boundary-layer exhibits a turbulent temperature profile, and can be split into a thin sublayer region in which most of the temperature change occurs, and an outer layer in which a shallow, linear temperature gradient exists.

The Chrysler Corporation is currently in the aerodynamic design phase of a slotted-wall automotive wind tunnel. This wind tunnel, with a 12-ft high by 20-ft wide test-section, is designed for aerodynamic, thermodynamic, and acoustic testing, and has a slotted-wall test section to minimize wall-interference effects. 1/12-scale tests were conducted on test sections with lengths of 51, 65, and 72 in. to determine the acceptable length of a slotted-wall test section having both turntable and dynamometer test positions. The effect of test-section length on the magnitude of the model pressure errors and the reference-speed correction required at the model and dynamometer positions, as well as the influence of the re-entry flaps on the test-section pressure gradient and on vehicle wake-development at the dynamometer position, were investigated. A test-section length of 72 in. (72 ft full-scale) was selected, based on the test results.

This paper presents numerical and experimental studies that support the detailed design-development of the automotive adaptive-wall test section. The areas studied include an assessment of the interaction of the wiper blades in an adaptive-wall test section with the vehicle wake, and the effect of actuator positioning errors on vehicle pressure-simulation accuracy. These studies showed that the errors induced by these test section design features on vehicle pressure-simulation were negligibly small. Also presented is the development of a one-step adaptive-wall algorithm, which adapts the test section walls to the final deflected position in just one iteration.

This paper presents a numerical model consisting of a two-dimensional, inviscid, stream-function vorticity code with a slotted-wall boundary condition. The model can be used to predict vehicle pressure-simulation accuracy in a slotted-wall automotive wind tunnel for a range of test section configurations. The vehicle and its wake were modeled as a combination of a doublet and a wake source, and the slotted-wall boundary condition was calibrated using published experimental data. Despite its inherent approximations, this model produces results that agree remarkably well with magnitudes and trends observed in published experimental data. This model was used to determine the length needed for a slotted-wall test section containing both a turntable and a dynamometer for aerodynamic as well as thermodynamic testing capability. Tests were conducted on a 1/12-scale slotted-wall test section to confirm the test section length predicted by the numerical model.