Session: 34-06 Axial compressor design methods

Paper Number: 128637

128637 - Acoustic Excitation As a Flow Control Technique in a High-Speed Compressor Cascade 

Acoustic excitation as a means of flow control has been successfully demonstrated in low to moderate subsonic flows over isolated aerofoils and low-pressure turbines. However, in transonic compressor cascades that operate high-speeds representative of a real aeroengine operating conditions, the use of acoustic excitation for flow control has not yet been investigated. Compressor cascades are often exposed to flow separations and, hence, performance degradations at off-design operating conditions. Therefore, control of flow separation at compressor off-design conditions can provide considerable improvements on the design of axial compressors. The motivation of this work is to investigate the effect of acoustic excitation on flow loss mechanisms on a linear compressor cascade at high speeds representative of aeroengines.

This work is based on a computational approach by use of IDDES (Improved Delayed Detached Eddy Simulation) for modelling the flow over an engine representative NACA65-K48 linear compressor cascade. The operating conditions for the cascade are Ma=0.67 and Re_c=560,000 based on the chord length and i = 4^o. A significant portion of the cascade passage is dominated by the separated flow, which results in passage blockage and high levels of total pressure losses. Therefore, accurate modelling of the uncontrolled flow field plays a critical role in application of acoustic excitation as the effective excitation frequencies are estimated from the uncontrolled flow. Furthermore, unsteady and three-dimensional nature of the uncontrolled flow and modelling of acoustic wave and flow interactions require a sophisticated turbulence modelling approach as observed in several previous studies. IDDES, being a hybrid RANS/LES model, is shown to provide the required order of accuracy. The uncontrolled flow is excited with sound waves in the form of both external and internal excitation by use of transient boundary conditions. The effectiveness of acoustic excitation is investigated for two main excitation parameters: excitation frequency and amplitude. The dominant frequencies in the uncontrolled flow frequency spectra are used as the initial excitation frequencies whilst a range of excitation amplitudes are considered for both external and internal acoustic excitation.

The results indicated that both external and internal acoustic excitation have changed the shear layer development in the cascade passage with a significantly upstream roll-up and breakdown of the shear layer compared to the uncontrolled flow. It has been observed that the shear layer and hence the coherent vortices are located away from the separated flow region in external acoustic excitation, resulting in no major momentum transfer across the shear layer to the separated flow region. Internal acoustic excitation, on the other hand, has a more profound effect that the shear layer roll-up and breakdown take place at a greater upstream location compared to the external excitation. As a result, more coherent vortices are generated that improve the momentum transfer across the shear layer to energize the separated flow. In overall, no major improvement in the total pressure losses is observed for acoustic excitation whereas ~16% reduction in the peak total pressure loss coefficient in the case of internal acoustic excitation. It is anticipated that current study can propose a new approach on the control of flow separation by means of sound excitation that can help improve the three-dimensional design and performance of high-speed compressor cascades.

Presenting Author: David John Rajendran Cranfield University

Presenting Author Biography: David John is a Lecturer within the Rolls-Royce University Technology Centre for Aero Systems Design, Integration and Performance at Cranfield University. He specialises in aero systems design for future propulsion architectures. David graduated with distinction in his bachelor's degree in Aeronautical Engineering from Madras Institute of Technology, India. After his graduation, he worked at the Gas Turbine Research Establishment in the design and development of turbines for various applications. Thereafter, he enrolled in the Gas Turbine Technology Master's degree at Cranfield University. In his Master's programme, his research looked into the turbine aerodynamic behaviour in overspeed conditions. Subsequently, he did his doctoral research within the Rolls-Royce University Technology Centre at Cranfield University where he explored the design space of using Variable Pitch Fans for reverse thrust in future efficient, environment friendly, civil gas turbines.

David has received several prestigious awards in both the academia and the industry like the stipendiary fellowship of the Aeronautics Research and Development Board, Government of India 2009, Rear Admiral A K Hando Trophy 2010, Government of India Young Scientist Award 2014, Royal Aeronautical Society (RAeS) NE Rowe Award 2016 and Cranfield Branch Annual Lecture Award 2016, Roy Fedden Memorial Prize 2017, American Society of Mechanical Engineers (ASME) Turbo Expo Best Paper Awards 2019 and 2020, Lord Kings Norton Medal 2020, and the ASME John P Davis Award 2020 and 2021. He has a total of 22 high impact journal and conference publications along with a editorial role for a special issue of Journal of Aerospace Sciences and Technologies. He has jointly filed 10 patent applications to date. He is a Member of the RAeS, ASME and the Aeronautical Society of India. He has been member of several peer review and preliminary design review committees, concept study and funding bid development teams, and has contributed in the organization of several high profile conferences and working committees. He is a peer-reviewer for several International gas turbine conferences, Journal of Aerospace Sciences and Technologies and the ASME Turbo Expo.

Authors:

Seyfettin Coskun Cranfield University
David John Rajendran Cranfield University
Vassilios Pachidis Cranfield University
Marko Bacic Rolls-Royce plc.