Study Of Crossflow Instability In The Boundary Layer Of Swept RAE2822 Wing

Crossflow is the main mechanism leading to laminar/turbulence transition on swept wing boundary layer flow.The design,optimization and drag reduction of airfoil require a deep understanding of the crossflow instability.Many parameters,such as Mach number,sweep angle,angle of attack,and Reynolds number,could affect crossflow instability.This paper studied the influence of sweep angle and angle of attack on the crossflow instability of swept RAE2822 wing with constant lift coefficient.The model used is the supercritical RAE2822 wing.The parameters used are that of cruise condition.The aerodynamic characteristics of the swept wing are obtained by solving Navier-Stokes equations;the sweep angle and angle of attack are adjusted to guarantee a constant lift coefficient;the boundary layer flow is obtained by solving quasi-3D boundary layer equations;the stability characteristic of the crossflow are analyzed by liner stability theory;the transition positions are predicted using eN method;the non-parallel effect of the base flow is investigated using NPSE;the nonlinear evolution of crossflow vortex is studied by DNS.The stability analysis and Reynolds Average Navier-Stokes simulation are combined to investigate the influence of transition on drag coefficient of the swept wing.Suggestions are proposed for the sweep angle selection in industrial design.It was found that,the equation based on simple sweep theory and lift line theory has some discrepancy with numerical results.Its accuracy can be improved by expressing the lift slope as a linear function of sweep angle.With constant lift coefficient,the strength of the crossflow increases as sweep angle becomes larger.The N factor increases accordingly.Transition happens firstly on the windward of the wing.There are two jumps in the drag coefficient as the increase of sweep angle.The wall curvature can stabilize crossflow instability,and can reduce the growth rate by half.The non-parallelism can destabilize the base flow and increase the growth rate almost one third.The mean flow distortion induced by crossflow vortex can change the instability characteristic of the base flow,and therefor increases the growth rate and the growth region of TS wave.It is recommended to consider crossflow instability and TS instability at the same time in the laminar wing design.