Numerical investigation of the effect of triangular cavity on the unsteady aerodynamics of NACA 0012 at a low Reynolds number

Abstract

Time accurate numerical simulations were conducted to investigate the effect of triangular cavities on the unsteady aerodynamic characteristics of NACA 0012 airfoil at a Reynolds number of 50,000. Right-angled triangular cavities are placed at 10%, 25% and 50% chord location on the suction and have depths of 0.025c and 0.05c, measured normal to the surface of the airfoil. The second-order accurate solution to the RANS equations is obtained using a pressure-based finite volume solver with a four-equation transition turbulence model, γ–Re θt, to model the effect of turbulence. The two-dimensional results suggest that the cavity of depth 0.025c at 10% chord improves the aerodynamic efficiency ( l/d ratio) by 52%, at an angle of attack of α = 8°, wherein the flow is steady. The shallower triangular cavity when placed at 25%c and 50%c enhances the l/d ratio by only 10% and 17%, respectively, in the steady-state regime of angles of attack between α = 6° and 10°. The deeper cavity also enhances the l/d ratio by up to 13%, 22% and 14% at angles of attack between α = 6° and 10°. Even in the unsteady vortex shedding regime, at α =12° and higher, significant improvements in the time-averaged l/d ratios are observed for both cavity depths. The improvements in l/d ratio in the steady-state, pre-stall regime are primarily because of drag reduction while in the post-stall, unsteady regime, the improvements are because of enhancements in time-averaged C l values. The current finding can thus be used to enhance the aerodynamic performance of MAVs and UAVs that fly at low Reynolds numbers.

Effect of spanwise groove on the dynamic stall characteristics of an airfoil

“…As can be seen in Figure 3(b), the results from the present numerical analysis is in decent agreement with the experimental results of Lee, 29 for the oscillating airfoil. Some disagreement seen in the lift values during the downstroke is common to the numerical simulations, 39,40 as small oscillations occur due to reattachment and re-laminarization, which is not observed in experiments. Even a heavy dependence of the numerically predicted lift values on the freestream turbulent intensity makes it extremely difficult to match the experimental values during the downstroke.…”

“…Recently Yadav and Bodavula reported an enhancement of 52% in the aerodynamic efficiency of NACA 0012 with a triangular groove at 10% chord, at a low Reynolds number of 50,000. 39 The reduction in aerodynamic efficiency reported in literature comes primary from the drag reduction as the cavity act as turbulence enhancer causing greater attachment of flow. 37,39 Despite clear favorable influence of grooves on airfoil aerodynamics in the static case, only few researchers have investigated the effect of this passive flow control devices for dynamic cases.…”

“…39 The reduction in aerodynamic efficiency reported in literature comes primary from the drag reduction as the cavity act as turbulence enhancer causing greater attachment of flow. 37,39 Despite clear favorable influence of grooves on airfoil aerodynamics in the static case, only few researchers have investigated the effect of this passive flow control devices for dynamic cases. In an experimental study by Chaudhry et al, it was found that the passive flow control devices viz.…”

Aerodynamic Performance Assessment of an Airfoil at Reynolds Number 10000: A Computational Approach

“…Although many researchers have attempted to use different types of indentations of different sizes, depths, and placement types, both above and below a surface, to summarize this, the depths of a single type of cavity can be tested on different regions of an airfoil surface. Numerical investigation done on the triangular cavity type by Bodavula A, helped gain valuable insights on the effect of adding either cavity and protrusions on the cavity on the airfoil body also helped choose a pre-existing design for the test airfoil [17,18,19]. Provided the research on the solver model done by the former, which employs transition Shear Stress Transport equations to stabilize the solution with the transport equations, this is deemed as an efficient method for getting accurate results in a fluid simulation [20,21].…”