Investigation of compressibility effects on dynamic stall of pitching airfoil

Abstract

In the present work, effects of compressibility on the dynamic stall of NACA 0012 airfoil, pitching sinusoidally from 5.03° to 24.79°, are investigated computationally using implicit large eddy simulations in a finite difference framework. Simulations of two-dimensional (2D), high Reynolds number, compressible flows are carried out without any transition or turbulence model to capture the physics of the dynamic stall process. The problem is formulated in a body-fixed, rotating, non-inertial frame. High accuracy, dispersion relation preserving optimized upwind compact scheme is used to compute convective flux derivatives, and an optimized three-stage Runge-Kutta method is used for time integration. Results are presented for free stream Mach number M∞ = 0.283, 0.4, and 0.5, where the Mach number is varied independent of the Reynolds number. The computations have been quite successful in capturing the essential features of the dynamic stall mechanism. It is observed that dynamic moment and lift stalls occur at smaller angles of attack as the Mach number increases. Reduction in the size of airload hysteresis loops and maximum attainable load coefficients are observed with increasing Mach number. Weak shock waves are observed near the leading edge (LE) at M∞ = 0.4, and lambda-shock is formed near the LE for M∞ = 0.5. It is observed that with increasing Mach number, the impact of dynamic stall on the aerodynamic loads (Cl, Cd, and Cm) becomes less dramatic as the maximum value attained by these aerodynamic loads decreases with an increase in the Mach number. An increase in positive damping area in the hysteresis loop is observed with an increase in the Mach number, inhibiting possible vulnerability to stall flutter.

Analysis of the onset and evolution of a dynamic stall vortex on a periodic plunging aerofoil

“…It is observed that compressibility acts on the sense to attenuate the aerodynamic loads in the hysteresis loop while maintaining their maximum and minimum values, a trend that was also observed by Sangwan et al. (2017) for a two-dimensional simulation of a pitching aerofoil. Here, we observe that the largest changes in and occur when the effective angle of attack is reduced from to , which corresponds to the time interval when the aerofoil is ceasing its downstroke motion.…”

“…Although different compressible regimes are studied, aspects of shock-induced separation are not present in the flows of interest here since they would alter the underlying onset mechanisms. For a comprehensive parametric study of compressibility effects on dynamic stall, the reader is referred to Bowles (2012), Bowles et al (2012), Corke & Thomas (2015), Sangwan, Sengupta & Suchandra (2017) and Benton & Visbal (2020).…”

“…For a comprehensive parametric study of compressibility effects on dynamic stall, the reader is referred to Bowles (2012), Bowles et al. (2012), Corke & Thomas (2015), Sangwan, Sengupta & Suchandra (2017) and Benton & Visbal (2020).…”

Passive Flow Control of Rotary-Wing and Fixed-Wing Aircraft Airfoils Via Surface-Based Trapped Vortex Generators

“…This is due to the occurrence of transonic flow and shock-induced boundary layer separation on the upper surface well below the "classical" dynamic stall angle of attack. This means that compressibility effects dominate the stall mechanism, a fact supported also in the literature, for example in[109] and[110].…”

Arbitrary Lagrangian–Eulerian formulation of lattice Boltzmann model for compressible flows on unstructured moving meshes

“…It is also shown that the present model is able to capture dual-mode vortex street, in close resemblance with the experiment. The formation of dynamic stall vortex (DSV) 45 near the leading edge of the airfoil is also observed In order to validate the results quantitatively, we compare the time history of the aerodynamic forces computed over several periods by the present model with that of the SD-NS solver 43 ; excellent agreement is observed. As it is shown in Fig.…”