Ground Effect on the Decay of Viscous Vortex Wakes

• Main Authors: Ji-Han Hsieh, 謝季翰
• Other Authors: Sheng-Jii Hsieh
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/88701480527261927947

碩士 === 國立成功大學 === 航空太空工程學系 === 88 === Large aircraft generates strong vortex wakes in the air, and the wakes have great effects on the following airplane. The vortex wake flows due to near ground flight, or take-off/landing of aircrafts plays an important role of airport management and the separation of aircrafts during approach or departure. A numerical flow simulation on the viscous vortices is studied to investigate the decay of this viscous vortex flow due to ground effect. The three-dimensional Navier-Stokes equations are solved by the CFD-2000 software to simulate the trajectory, development and decay of vortex wakes generated by the wing near the ground, and the wing has NACA0012 profile, and with aspect ratio 6. To investigate factors effecting vortex wakes, this study uses two different methods for numerical simulations: (1) complete flow field computation, and (2) compound flow field computation. In the complete flow field computation, the computational domain contains the semi-span wing and the wake flow region of one hundred chords after wing trailing edge. The complete flow fields at different ground boundary conditions, Reynolds numbers, laminar flow or turbulent flow, are studied to investigate the development of trailing vortex wakes. In the compound flow field computation, the computational domain is divided into two parts. The first part contains the wing and the near wing trailing vortices. The second part is the downstream wake flow. The flow is assumed laminar, the Reynolds number is 4.16e6 and the flow is unsteady. The computation of the first part starts from upstream of the wing and stops at three chords distance after the wing trailing edge, where three kinds of flow data at different times are taken as the in-flow boundary conditions for the second part downstream wake flow computation. In the simulation results of the complete flow field computation, it is found that the vorticity distribution and the lateral movement of the vortex wakes are affected by ground effect, and the decay of vortex wakes is more pronounced. The effect of turbulence makes vortex wake flow more inviscid in character, but the prediction of the vortex wakes trajectory is smaller then those of laminar and inviscid wake flows. It is noted that, in the compound flow field computation, the vortex shedding from the wing behaves as the secondary vortex effect on the trajectory of the vortex wake flow.