Numerical Research On High-Order Schemes With Low Dissipation For Unsteady Helicopter Rotor Flows

Accurate Navier-Stokes simulation of rotary-wing aerodynamics remains one of the most challenging tasks due to the strong and complex vortex wake system that lingers in the vicinity of the rotor. The issue in rotor computational fluid dynamics needs to be tackled for the healthy growth of the helicopter industry. Traditional low-order, spatially accurate Euler/Navier-Stokes computational methodologies tend to dissipate the vortex wake system due to excessive numerical dissipation inbuilt in such numerical schemes, which causes the tip vortex to be captured with much less intensity than the physical reality. Therefore, it's very difficult to accurately predict the aerodynamic, aeroacoustic, and aeroelastic properties. One of the central issues facing the future of first-principles based Navier-Stokes simulation as a practical and useful tool for rotorcraft issues is the ability to capture vorticity without numerical dissipation. In this paper, low numerical dissipation and high order accurate methods have been studied to investigate flowfield around rotor in hover and forward flight.The main research work and increasing contribution of this dissertation are listed as follows:1. The construction of high order accurate WENO (Weighted Essentially Non-oscillatory) schemes is studied on structured mesh. We describe the choice of stencil, construction and accurate order of interpolation polynomial for one- dimensional hyperbolic conservation laws, and then develop them for two- dimensional hyperbolic conservation laws. The performance of the schemes has been assessed in typical problems, which reveals that fifth-order WENO schemes have the great capabilities to capture shock and contact discontinuities with high resolution.2. An efficient, robust and accurate method for simulating steady/unsteady flows is developed and exerted to solve a variety of two-dimensional and three-dimensional viscous flows. All methods are implemented within framework of Finite-Volume method. A third-order MUSCL scheme and an improved fifth-order WENO scheme are adopted to interpolate higher order left and right states across a cell interface with Roe Riemann solver updating inviscid flux. Improved LU-SGS scheme and fully implicit dual-time stepping method are utilized for time integral. To improve the efficiency and stability for viscous flows, a viscous correction is introduced into LU-SGS scheme and a Newton-like scheme is obtained. Considering fifth-order WENO stencil with five cells, three layers of hole boundary and interpolation boundary are searched in overset grids between which flow field information can effectively exchange.3. An improved fifth-order WENO scheme has been successfully applied to helicopter rotor in hover for the first time in China. A high-order upwind scheme with low dissipation has been developed to compute the flow of hovering rotor. Primarily, implicit WENO scheme is applied to inviscid flow computation of hoveing rotor based on one single grid. Moreover, based on static overset grids, the implicit WENO scheme is developed to compute viscid flow around rotor in hover for capturing vortex wake. The tip vortex structures are better captured with the present approach in comparision with analogical computation case. For transonic flow with 8 collective pitch, the tip vortices denoted by vorticity contours at vorticity between 0.1 to 1 are excellently conserved up to wake age of 810 , and tip vortex center position with vortex age is agreement with experiment data. For subsonic flow with 12 collective pitch, the tip vortices are conserved up to wake age of 765 , and tip vortex center position with vortex age is agreement with that given by Kocurek's wake-fitting formula in free air. Compared with MUSCL scheme, WENO scheme proves to conquer vortex wake dissipation to a greater degree.4. A low dissipation approach based on fifth order accurate WENO scheme has been developed to simulate unsteady viscous flow around helicopter rotor in forward flight, which becomes one of scarce works on using similar methods. An efficient code is explored based on a moving overset grids and fully implicit dual-time stepping method. Grid velocity adopts analysis method for avoiding too much numerical interpolation error. The computational results reveal that the present method has a certain efficiency and low dissipation.