Session: 32-01 Flow Control

Paper Number: 152425

Transonic Linear Cascade Demonstration of Acoustic Flow Control on High Work and Lift Turbines 

The study presented explores acoustic flow control in high-lift, high-work turbine blades at transonic speeds. The turbine blades, L3FHW-HS and L4FHW-HS, were tested in a transonic linear cascade facility to address challenges in controlling flow separation, a significant issue at low Reynolds numbers due to the occurrence of high adverse pressure gradients. This study builds upon previous work in low-speed flow control and extends it by introducing acoustic excitation to control separated flows at transonic speeds.

Acoustic excitation aims to focus on frequencies associated with the Kelvin-Helmholtz instability, which scales with the 3/2 power of the exit Mach number. Two different acoustic sources were utilized: an in-house siren disk and a passive perforated tailboard, which functioned as a Helmholtz resonator. The siren disk produced acoustic waves through periodic interruption of a supersonic jet, generating frequencies between 1-53 kHz at sound pressure levels (SPL) of up to 140 dB. The perforated tailboard, designed to reflect sound waves, generated tonal noise at high SPLs without the need for additional mass flow. Both mechanisms were tested for their effectiveness in controlling the separated shear layer over the turbine blades. 

The experiments were conducted across a range of Mach numbers, with extensive data gathered through Schlieren imaging and static pressure measurements. The study found that acoustic excitation significantly influenced the flow dynamics by altering the shear layer's structure. In particular, the vortical structures within the shear layer were strengthened, leading to a notable decrease in the angle of the separated shear layer. This indicates a successful control of massively separated flows, with reductions in the separation angle of up to 20° observed at lower Mach numbers. The spectral analysis, including short-time Fourier transform (STFT) and spectral proper orthogonal decomposition (SPOD), revealed that acoustic excitation increased the energy content in the separated shear layer. The results showed that acoustic waves could energize the flow, amplifying the unsteady vortical structures. 

Presenting Author: John Clark Airforce Research Laboratory

Presenting Author Biography: Dr. John Clark is the Principal Engineer and Lead Researcher in Turbines for the Turbine Engine Division in the Aerospace Systems Directorate at the Air Force Research Laboratory (Wright-Patterson Air Force Base, Dayton, OH, USA). He was awarded the degree of Doctor of Philosophy from the University of Oxford where he was a student of Prof. Terry Jones at the Osney Turbomachinery Laboratory. Subsequent to his graduate education he worked at United Technologies, Pratt & Whitney in the Turbine Aerodynamics group. From there he joined the Air Force Research Laboratory in 2002. Dr. Clark has more than 70 journal publications and refereed conference papers on the topics of unsteady aerodynamics in turbomachines, high- and low-pressure turbine aerodynamics, turbine design methods and applications, optimization of turbine components, boundary-layer transition modeling, and turbine heat transfer and cooling. These efforts have so far generated 4 US patents and one pending. Since 2013 Dr. Clark has served as Associate Editor of the ASME Journal of Turbomachinery. Also, in 2012 he was selected by the American Institute of Aeronautics and Astronautics as the Engineer of the Year in part for his efforts to improve the understanding of unsteady shock interactions in turbines.

Authors:

Acar Celik Technion-IIT
Abhijit Mitra Technion-IIT
John Clark Airforce Research Laboratory
Beni Cukurel Technion-IIT