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Aerodynamic Investigation on the Excitation of a Laminar Separation Bubble by Secondary Jets

[+] Author Affiliations
Samson AnnapuReddy, S. Sarkar

Indian Institute of Technology Kanpur, Kanpur, India

Paper No. GT2014-26115, pp. V05CT17A003; 11 pages
doi:10.1115/GT2014-26115
From:
  • ASME Turbo Expo 2014: Turbine Technical Conference and Exposition
  • Volume 5C: Heat Transfer
  • Düsseldorf, Germany, June 16–20, 2014
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4573-8
  • Copyright © 2014 by ASME

abstract

Aerodynamic interactions of a separated shear layer from the semi-circular leading edge of a constant thickness aerofoil model with jets ejecting in the vicinity of reattachment from a row of discrete holes at an angle of 30° in the streamwise direction are elucidated. Experiments are carried out for two Reynolds numbers (ReD) 25000 and 55000 (based on the leading-edge diameter) and two velocity ratios (V.R) 0.5 and 1. The time-averaged velocity and turbulence quantities are measured using Laser-Doppler Anemometry (LDA) at different streamwise locations along the centre line of the jet, while the instantaneous flow filed is obtained using Particle Image Velocimetry (PIV). Measurements reveal that the flow undergoes separation at the blending point of semi-circle and flat plate owing to sudden change in geometry. It is observed that in the absence of the jet, the separated shear layer undergoes transition with formation Kelvin-Helmholtz (K-H) rolls and a significant growth of Reynolds stress in the second-half of the bubble is evident. With injection, the separation bubble length in the upstream of jet has decreased with increased growth rate of velocity fluctuations. However, the characteristics of the flow in the separated region remains almost unchanged and the transition criteria even follows the universal intermittency characteristics of Dhawan and Narasimha [35]. The instantaneous results elucidate that K-H rolls from the separated shear layer interact with the injected jet resulting in its oscillation. In the downstream of injection, the presence of the jet is felt with enhanced turbulence activities in the outer layer, particularly for high V.R. Further, the onset and end of transition of the separated flow are compared with correlations available in the literature.

Copyright © 2014 by ASME

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