No abstract

Here, Direct Numerical Simulation (DNS) of low Reynolds number (Re) flow in the presence of free stream turbulence (FST) pertaining to micro-aerial vehicle (MAV) is reported. The focus is on numerically simulating the flow around an airfoil at low Re to understand its behaviour using high accuracy compact schemes (T. K. Sengupta, High Accuracy Computing Methods, Cambridge University Press, New York, 2013.) [1]. In low Re aerodynamics, the flow is characterized by unsteady separation bubbles and vortex shedding from the suction surface and the trailing edge as well, which make it different from high Re aerodynamics. The maximum attainable lift coefficient and lift-to-drag ratio decreases drastically at low Re, as compared to high Re flows. Such flows are also important because of their susceptibility to background disturbances. Stalling of aircraft wing is one such phenomenon where free stream turbulence (FST) plays a crucial role. In this work, effects of FST, effects of Re and angles of attack  are studied with respect to flow separation and vortex shedding. Flow characterization is done for the AG24 airfoil, at Re =60,000 and 400,000, with and without consideration of FST in the range of angles of attack, 6 6The computational results are compared with the experimental results of Williamson et al. ( Summary of Low Speed Airfoil Data, volume 5, Dept. of Aerospace Engineering, UIUC, 2007 ) [2] and are found to be in good agreement. Flow simulation over AG24 airfoil is performed here via parallel computation, using high accuracy compact schemes for spatial discretization and optimized Runge-Kutta (ORK4) scheme for time marching [1]. This paper also discusses proper implementation of filters and FST model.

No abstract

The effects of single dielectric barrier discharge (SDBD) plasma actuators on flow control are studied using a new frequency and pressure dependent capacitance based model by calculating the spatio-temporal distribution of surface charge density in the present work. The proposed model is an improvement over earlier similar efforts, while retaining the superior features of previous macroscopic models. It can be used to accurately compute the spatio-temporal distribution of body force due to plasma actuation without computing the complex electrodynamics equations for charge density on microscopic scales. It has been shown that the proposed model estimates the time-averaged total body force more accurately than similar models developed earlier, as compared to experimental results. We have also considered the effects of plasma excitation frequency and the voltage wave-form. The proposed model has been incorporated into a Navier-Stokes equation (NSE) solver in time-accurate manner to study SDBD plasma actuation in a quiescent flow environment. The onset of plasma actuation causes creation of a complex transient vortical flow field, one of its actions is to create a wall-jet. Computed instantaneous velocity profiles at downstream locations show this wall-jet and are compared with the experimental results. Computed results of the evolution of a starting vortex in a quiescent air induced by initiation of SDBD plasma actuation, displays an excellent match with experimental results of Whalley and Choi (J. Fluid Mech., 703, 192-203, 2012).

No abstract