Wake Dynamics of Finite Aspect Ratio Wings. Part II: Computational Study

Abstract

As the second part of a three-part joint research, direct numerical simulations have been performed to study the three-dimensional wake dynamics of finite NACA0015 wings at a chordbased Reynolds number of 400. With the imposition of the symmetry boundary condition on the root plane, we identify three major behaviors of vortical structures, namely, the tip vortex at the free end, spanwise shedding vortices near the root, and the interaction vortices in between. The tip vortex is persistent among all the investigated cases. Its intensity is largely affected by the angle of attack and less affected by the aspect ratio. The spanwise periodic shedding is revealed for AR = 4. Further increasing AR to 6 brings out the vortex dislocation in the spanwise shedding region. Spectral analysis to the wake velocity unveils two frequencies in the event of vortex dislocation. This leads to the beating phenomenon in the lift coefficient. Taking the form of vortex cores with mixed streamwise/crossflow vorticity, the interaction vortices are sandwiched between the tip vortex and the spanwise shedding region, and shed periodically with the same frequency as the spanwise vortices. Aerodynamic forces are also evaluated based on the available data. Compared with the 2-D cases, the tip effects not only reduce the force coefficients, but also cause a loss in the aerodynamic performance of the wings.

On the formation of three-dimensional separated flows over wings under tip effects

“…We further validate the present numerical results against those from another flow solver Nektar++ that is based on the spectral/hp element method (Cantwell et al 2015). The computation is carried out with an independent numerical set-up (He et al 2019;Zhang et al 2019). We compare the wake vortical structures obtained by Nektar++ (top) and Cliff (bottom) for the same case of (α, sAR) = (22 • , 4) at t = 9.25 in figure 4.…”

“…2019; Zhang et al. 2019). We compare the wake vortical structures obtained by Nektar++ (top) and Cliff (bottom) for the same case of at in figure 4.…”

Wake Dynamics of Finite Aspect Ratio Wings. Part III: TriGlobal Linear Stability Analysis

“…Our first goal is to establish a common point of departure for the parallel experimental, theoretical and numerical efforts. To this end, a given geometry and set of parameters have been chosen to make comparisons between the full three-dimensional flow field results obtained herein by the spectral element code nektar++, run in DNS mode, and the corresponding results obtained in Part II [4] by the finite volume code CharLES. At an arbitrarily chosen time, flow around an aspect ratio AR = 4 NACA 0015 wing has been computed at Re = 400 and AoA = 22 • by the two codes and the respective visualizations are compared in Fig.…”

Wake Dynamics of Finite Aspect Ratio Wings. Part I: An Experimental Study

“…In the present paper, flow visualization and SPIV were used on multiple geometric configurations, having a NACA0015 profile, to explore flow structures that are present in the wake. Comparison with computational and stability analysis will be done on select cases to cross-validate the results [12][13] which will eventually lead to the advancement of knowledge of three-dimensional separation. With this knowledge, the eventual goal is to optimally implement flow control devices onto vehicles to enhance their performance under various flight conditions.…”