Session: 05-07 Topics in Instrumentation (III)

Paper Number: 82344

82344 - Development of a Test Article for Acoustic Streaming in High-Speed Flow 

Aircraft engines require lightweight efficient thermal management devices to maintain high performances at high-pressure ratios. Acoustic streaming can provide a viable, lightweight solution to improve the heat exchangers' capacity with a reduced drag penalty. The present work aims at developing a test article to experimentally create large-amplitude acoustic pulsations at high frequencies, required for generating acoustic streaming, and to characterize its impact on the unsteady heat flux and shear stress within a narrow channel. This is accomplished by iteratively designing the test section and assessing the flow features via CFD calculations to converge to an optimal test model, as well as careful selection of measurement techniques to monitor the steady and unsteady flow properties. Using CFD calculations to revise each design iteration, instead of experimental testing, reduces the cost of developing the effective geometry.

The final test model consists of two long hollow plates placed in parallel and 2cm apart creating a narrow channel within a larger flow area. As a result, three flow paths are created within the wind tunnel’s test section and the area ratio between the main and the bypass flow controls the Mach number within the narrow channel. The leading edges of the plates are rounded, and the trailing edges are minimally slanted in order to avoid the flow separation that can severely affect the boundary layer within the narrow channel. The acoustic waves drive acoustic streaming and are generated by an open cavity with the length-to-dept ratio of L/D =2 which produces pressure oscillations with the dominant frequency of ~8 kHz in a Mach 0.8 flow.

Pressure taps and K-type thermocouples are used to monitor the pressure and temperature distributions over the walls while the total pressure and temperature are measured upstream of the plates. Kulite miniature pressure transducers measure the pressure fluctuations at high frequencies at the domain boundaries and near the open cavity. Optical shear stress sensors are selected to monitor the unsteady wall shear stress immediately downstream of the open cavity. A thin film sensor array is designed for high-frequency wall temperature measurements which serve as the boundary condition for inverse heat flux calculations. High-speed Schlieren imaging is taken to visualize the flow structures near the cavity region.

The experiments performed at the Purdue Experimental Turbine Aerothermal Lab indicate that the designed test article successfully reaches Mach 0.8, and the open cavity creates the high-amplitude pressure pulsations at the frequency of ~8 kHz. The successful commissioning sets the stage for future experiments to determine the potential of acoustic streaming as a low weight modification to improve compact heat exchangers.

Presenting Author: Michael Butzen Purdue University

Presenting Author Biography: Michael Butzen is a Research Engineer in Purdue Experimental Turbine Aerothermal Lab at Purdue University.

Authors:

Iman Rahbari Purdue University
Michael Butzen Purdue University
James Twaddle Purdue University
Guillermo Paniagua Purdue University