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Effects of compressibility, pitch rate, and Reynolds number on unsteady incipient leading-edge boundary layer separation over a pitching airfoil

Published online by Cambridge University Press:  26 April 2006

P. Ghosh Choudhuri  and
D. D. Knight
P. Ghosh Choudhuri
Affiliation:
Department of Mechanical and Aerospace Engineering, PO Box 909, Rutgers University, Piscataway, NJ 08855, USA
D. D. Knight
Affiliation:
Department of Mechanical and Aerospace Engineering, PO Box 909, Rutgers University, Piscataway, NJ 08855, USA
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Abstract

The effects of compressibility, pitch rate and Reynolds number on the initial stages of two-dimensional unsteady separation of laminar subsonic flow over a pitching NACA-0012 airfoil have been studied numerically. The approach involves the simulation of the flow by solving the two-dimensional unsteady compressible laminar Navier-Stokes equations employing the implicit approximate-factorization algorithm of Beam & Warming and a boundary-fitted C-grid. The algorithm has been extensively validated through comparison with analytical and previous numerical results. The computations display several important trends for the ‘birth’ of the primary recirculating region which is a principal precursor to leading-edge separation. Increasing the non-dimensional pitch rate from 0.05 to 0.2 at a fixed Reynolds number and Mach number delays the formation of the primary recirculating region. The primary recirculating region also forms closer to the leading edge. Increasing the Mach number from 0.2 to 0.5 at a fixed Reynolds number and pitch rate causes a delay in the formation of the primary recirculating region and also leads to its formation farther from the airfoil top surface. The length scale associated with the recirculating regions increases as well. Increasing the Reynolds number from 104 to 105 at a fixed Mach number and pitch rate hastens the appearance of the primary recirculating region. A shock appears on the top surface at a Reynolds number of 105 along with the simultaneous formation of multiple recirculating regions near the leading edge.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 308 , 10 February 1996 , pp. 195 - 217
Copyright
© 1996 Cambridge University Press

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