Experimental and Computational Steady and Unsteady Transonic Flows about a Thick Airfoil

Abstract

An experimental and computational investigation of the steady and unsteady transonic flowfields about a thick airfoil is described. An operational computer code for solving the two-dimensional, compressible Navier-Stokes equations for flow over airfoils was modified to include solid-wall, slip-flow boundary conditions to properly assess the code and help guide the development of improved turbulence models. Steady and unsteady fiowfieids about an 18% thick circular arc airfoil at Mach numbers of 0.720, 0.754, and 0.783 and a chord Reynolds number of 11 x 10 6 are predicted and compared with experiment. Results from comparisons with experimental pressure and skin-friction distributions show improved agreement when including test-section wall boundaries in the computations. Steady-flow results were in good quantitative agreement with experimental data for flow conditions which result in relatively small regions of separated flow. For flows with larger regions of separated flow, improvements in turbulence modeling are required before good agreement with experiment will be obtained. For the first time, computed results for unsteady turbulent flows with separation caused by a shock wave were obtained which qualitatively reproduce the time-dependent aspects of experiments. Features such as the intensity and reduced frequency of airfoil surface-pressure fluctuations, oscillatory regions of trailing-edge and shock-induced separation, and the Mach number range for unsteady flows were all qualitatively reproduced.

A Numerical Investigation of the Geometric Parametrisation of Shock Control Bumps for Transonic Shock Oscillation Control

“…Independent computational studies successfully have captured the inherent flow characteristics of transonic shock buffet using URANS modelling; however, prominent sensitivity to a variety of simulation variables has been observed [32][33][34][35][36][37][38][39]. The most pertinent of these was the choice of turbulence closure [35,[40][41][42], grid resolution local to the shock travel region [36,43,44], and the use of dual time-stepping with acoustic temporal resolution [43,45].…”

Landmarks and new frontiers of computational fluid dynamics

“…From the basic knowledge, the mixed elliptic-hyperbolic differential equation was solved by differencing formulas in the subsonic and supersonic regions to properly account for the local domain of dependence [53]. Equally important, outstanding CFD efforts have been exerted to explore previously unsolvable physics for airfoil buffet [54] and aileron buzz phenomena [55].…”

Periodic transonic flow and control

“…The aerodynamic performance of an aerofoil/wing subject to transonic periodic flows can be described by the onset of buffet, its amplitude, frequency and boundaries. The challenges in predicting buffet due to periodic motion (2)(3)(4)(5)(6)(7)(8)(9)22,24,(31)(32)(33)(34)(35) include (a) identification of a well-defined buffet boundary, (b) capturing the correct Tijdeman's type of shock induced oscillation, (c) capturing the correct location of the oscillatory region on the surface of the aerofoil, and (d) accurate prediction of the reduced frequency. The accuracy of the predictions by CFD depends on both the turbulence model and the temporal/spatial accuracy of the shock-capturing numerical discretisation scheme used, while the experimental results are subjected to wind-tunnel constraints.…”

“…It was concluded from this work that the use of a better turbulence model based on steady flow experiments can improve the predictions. The current CFD techniques for prediction of periodic transonic flows (2)(3)(4)(5)(6)(7)(8)(9)22,24,(31)(32)(33)(34)(35) are primarily based on two methods. The first method consists of solving the time accurate Reynolds Averaged Navier-Stokes (RANS) equations (24,26,29,38,40) directly using an implicit or explicit numeric scheme in conjunction with algebraic or non-linear turbulence models (or, more recently, using Large Eddy Simulation, LES).…”