Scaling Considerations for Fluidic Oscillator Flow Control on the Square-back Ahmed Vehicle Model

Improvements in highway fuel economy require clever design and novel methods to reduce the drag coefficient. The integration of active flow control devices into vehicle design shows promise for greater reductions in drag coefficient. This paper examines the use of fluidic oscillators for separation control at the rear of an Ahmed vehicle model. A fluidic oscillator is a simple device that generates a sweeping jet output, similar to some windshield wiper spray nozzles, and is increasingly recognized as an efficient means to control separation. In this study, fluidic oscillators were used to blow unsteady air jets and control flow separation on rear boat-tail flaps, achieving drag reductions greater than 70 counts. The method appears to scale favorably to a larger model, and realistic effects such as a rolling road appear to have a small impact on the oscillator's control authority. This paper will summarize the effects of geometric scaling and Reynolds scaling when applying fluidic oscillators to the Ahmed model. This work addresses some of the key scaling questions that must be answered while developing flow control schemes for full-scale automotive applications, and it is important to address these questions on a simplified Ahmed model before additional complexity is introduced through use of representative auto model geometries.