Edge Of Wing Pairs Of Vertical Tail Buffeting Experimental And Numerical Study

In this thesis, the twin-vertical-tails buffet of strake-wing layout which is the primary configuration of the new generation of fighter is investigated, by both wind tunnel experiments and numerical simulations.The wind tunnel experiments include four aspects:1) A wind tunnel investigation of twin-vertical-tails buffet of a strake-wing layout was conducted to study the test method of tail buffet. The test method include root bending moment measurement and tip acceleration measurement. The root-mean-square (RMS) values of root bending moment and tip acceleration were used to scale the buffet intensity. The characteristics of twin-vertical-tails buffet of the strake-wing layout was also studied in the test.2) A flow visualization experiment was conducted to study the vortex flow field of the strake-wing layout at high angles of attack, using a laser light sheet technique. Combining with the result of the vertical tail buffet characteristic obtained from the wind tunnel experiment, the visualization experiment came to the conclusion that: The bursting of the vortex shed from leading-edge-extension (LEX) is the primary contributor to the twin-vertical tail buffet.3) A wind tunnel investigation was conducted to study the unsteady pressures on the surface of the vertical tail in buffet. The unsteady pressures were integrated along the surface to yield the root bending moment of the vertical tail. The root bending moment computed from root bending strain was also discussed. Then the RMS bending moments measured by two different method were compared. Results show that they are consistent well with each other. So the unsteady load of vortex breakdown flow impinging on the vertical tail is the primary contributor of the vertical tail buffet.4) The last wind tunnel investigation was conducted to study the influence ofthe primary parameters of strake-wing layout on the twin-vertical-tails buffet, including the influences of sweep angle of LEX, sweep angle of wing, chord-wise and span-wise position of vertical tail on the buffet of vertical tail.The contents of numerical simulation of twin-vertical-tails buffet consists of three aspects:1) The LU-SGS implicit time-stepping scheme was used to solve 3-dimensional compressible Euler equations. Combining the grid reordering technology, a much higher efficient Euler equations solver for 3-D unstructured mesh was developed.2) The Roe scheme of flux difference splitting was used to discrete the spatial flux, this scheme could simulate the separated flow field at high incidence efficiently.3) The numerical simulation of the twin-vertical-tails buffet of several different strake-wing layout were conducted, using the time accurate unsteady Euler equations solver developed in the thesis. The development and breakdown of the LEX vortex was investigated, along with the unsteady pressures on both sides of the vertical tail. Then the unsteady pressures were integrated along the surface to yield the root bending moment of the vertical tail. The numerical simulation explained the mechanism and characteristics of twin-vertical-tails buffet of strake-wing layout in detail. And the results were consist well with experiments data, that proved the feasibility of Euler equations for simulating the vertex breakdown and the tail buffet caused by vertex breakdown or separated flow.