Fengjun Liu

Computational Modeling For The Transitional Flow Over A Multi-Element Airfoil

The transitional flow over a multi-element airfoil in a landing configuration are computed using a two equation transition model. The transition model is predictive in the sense that the transition onset is a result of the calculation and no prior knowledge of the transition location is required. The computations were performed using the INS2D) Navier-Stokes code. Overset grids are used for the three-element airfoil. The airfoil operating conditions are varied for a range of angle of attack and for two different Reynolds numbers of 5 million and 9 million. The computed results are compared with experimental data for the surface pressure, skin friction, transition onset location, and velocity magnitude. In general, the comparison shows a good agreement with the experimental data.

Spatial linear instability of confluent wake/boundary layers

The spatial linear instability of incompressible cone uent wake/boundary layers is analyzed. The e ow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr‐Sommerfeld equation is solved using a global numerical method for the resulting eigenvalue problem. The numerical procedure is validated by comparing the present solutions for the instability of the Blasius boundary layer and for the instability of a wake with published results. For the cone uent wake/boundary layers, modes associated with the boundary layer and the wake, respectively, are identie ed. The boundary-layer mode is found to beamplie ed as thewake approaches the wall. On theother hand, the modes associated with the wake, including a symmetric mode and an antisymmetric mode, are stabilized by the reduced distance between the wall and the wake. An unstable mode switching at low frequency is observed where the antisymmetric mode becomes more unstable than the symmetric mode when the wake velocity defect is high.

Computational modeling for the flow over a multi-element airfoil

The flow over a multi-element airfoil is computed using two two-equation turbulence models. The computations are performed using the INS2D) Navier-Stokes code for two angles of attack. Overset grids are used for the three-element airfoil. The computed results are compared with experimental data for the surface pressure, skin friction coefficient, and velocity magnitude. The computed surface quantities generally agree well with the measurement. The computed results reveal the possible existence of a mixing-layer-like region of flow next to the suction surface of the slat for both angles of attack.

Compressible Linear Stability of Confluent Wake/Boundary Layers

The linear stability of a compressible confluent wake/boundary layer is studied. The base flow model considered is the superposition of a compressible boundary layer and a Gaussian-like wake located above the boundary layer. The linear stability equations have been solved by using a global numerical method. The stability modes of interest have been identified as the boundary-layer modes, the antisymmetric wake mode, and the symmetric wake mode. The effects of wake height on the first Tollmien-Shlichting mode and the second mode associated with the boundary layer are discussed. Results for unstable modes associated with the wake are also presented

NUMERICAL CALCULATION OF THE TRANSITIONAL FLOW OVER A HYDROFOIL

The incompressible transitional flow fields over a naval hydrofoil at operational Reynolds numbers are calculated by using a RANS solver with a predictive transition model. In the experimental study of the hydrofoil, transitional boundary layers were found for Reynolds number up to 50 million. The transition model used here has been applied to predict bypass transition of flat plate boundary layers and natural transition over a high-lift, multi-element airfoil for Reynolds number up to 9 million. In this paper, the results of applying the same model to predict the high Reynolds number hydrofoil flow transition are reported. The transition onset locations on both the suction side and the pressure side of the hydrofoil were predicted. The transition onset predictions generally agree well with the experimental data. In addition, the calculated velocity profiles, separation points and the separation bubble sizes match well the data, which indicates the capability of the transition model to predict boundary layer transition at low speed and high Reynolds number.