Experimental Assessment of Trans Sonic Rossiter Cavity in Developing Acoustic Streaming and its Effects On Heat Transfer

James Twaddle, Purdue University

Abstract

Acoustic streaming is a phenomenon which occurs when acoustic excitations interact with a fluid (stationary or non-stationary). Exploitation of this phenomenon has the potential to open doors to new methods of flow control through the enhancement or diminishment of the present flow instabilities. A particular use of acoustic streaming shown by previous numerical studies is the enhancement of heat transfer in violation of the Reynold’s Analogy within a small range of Mach numbers and frequencies of periodic excitation. The focus of this thesis is to experimentally assess the usage of a Rossiter cavity in generating periodic acoustic excitations and its effects on the shear stress and heat transfer. In the present research, two large models are tested using a blow-down facility. The models are made of aluminum and Teflon and were developed to ensure optical access for infrared thermography. The geometries are tested at Mach number ranging from 0.373 to 0. 866. The target Mach number-frequency pair where significant heat transfer enhancement is a free stream Mach number at the cavity, Mc, of 0.75 and the frequency, fc, of 7.5 kHz. The cavity is tuned using the Rossiter equation with Rossiter constants k = 0.66 and y = 0.25. The heat transfer and skin friction enhancement are measured immediately upstream and downstream of the cavity and compared to the previous numerical studies. When testing the Teflon model with an ambient back pressure and 11 lb/s mass flow, a frequency of 7.8 kHz was generated by the cavity. For the aluminum model tested at a high vacuum and 3 lb/s mass flow, frequencies near 7, 10, and 20 kHz were generated by the cavity with 10 and 20 kHz appearing most often. High speed schlieren imaging was used to confirm the flow structures being generated in the flow. There was good agreement with the Rossiter modes at lower Mach numbers and moderate agreement at transonic Mach numbers. A correlation is presented which defines a band of Mach number-Reynolds number pairs which present with a discontinuous frequency behavior during operation of the wind tunnel. Measurable effects on both skin friction and heat transfer between tests with comparable operating conditions to a reference were observed and are presented.

Degree

M.Sc.

Advisors

Paniagua, Purdue University.

Subject Area

Design|Acoustics|Aerospace engineering|Atmospheric sciences|Fluid mechanics|Mathematics|Mechanics|Polymer chemistry|Thermodynamics

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