Modeling and Analysis of Shock Reduction through Counterflow Plasma Jets

The study presents a numerical investigation of aerodynamic drag reduction by implementing a counterflow plasma jet, emanating from the stagnation point of an aerodynamic surface in a supersonic regime with a constant pressure ratio , and compares findings with a conventional opposing jet. The computational study is carried out by solving three-dimensional and axisymmetric Navier–Stokes equations for counterflow plasma-jet interaction. The calculations are performed at free-stream Mach ( = 1.4) with sea level stagnation conditions. The weakly ionized argon plasma jet generated by a plasma torch has constant stagnation pressure and temperature of and . The effect of the Mach number and the angle of attack variation on plasma-jet effectiveness is also analyzed. The results indicate that the counterflow plasma jet reduces more drag (in twice) compared to the conventional jet (nonplasma). The gravitational, magnetic field effect and chemical processes in the plasma formation are considered negligible. It is inferred that the effectiveness of the counterflow plasma jet strongly depends upon the jet stagnation temperature

Numerical investigation of passive flow control around a D-shaped bluff body

A passive flow control around a two-dimensional D-shaped bluff body is studied at a Reynoldsnumber of 13 000 using large eddy simulation with the Coherent Structure Model (CSM). A small circularcontrol cylinder located in the near wake region behind the bluff body is employed as a local disturbanceof the shear layer and the wake. Numerical results are compared with experimental data in detail, includingglobal flow paramters of drag coefficient as well as mean and RMS velocities. The predictions suggest thatthe bubble recirculation length is significantly increased by the local disturbance of the small cylinder. Adrag reduction of about 27.6% is observed in the numerical simulation. The small control cylinder wasfound to split the shear layer detached from the main bluff body and result in the flow structure like a jetwhich inflates the formation of the wake region behind the main bluff body

Large Eddy Simulation of Flow Control Around a Cube Subjected to Momentum Injection

The concept of Momentum Injection (MI) through Moving Surface Boundary layer Control (MSBC) applied to a cubic structure is numerically studied using Large Eddy Simulation at a Reynolds number of 6.7 7104. Two small rotating cylinders are used to add the momentum at the front vertical edges of the cube. Two configurations are studied with the yaw angle of 0\ub0 and 30\ub0, respectively, with ratio of the rotation velocity of cylinders and the freestream velocity of 2. The results suggest that MI delays the boundary layer separation and reattachment, and thus reduces the drag. A drag reduction of about 6.2 % is observed in the 0\ub0 yaw angle case and about 44.1 % reduction in the 30\ub0 yaw angle case. In the case of 0\ub0 yaw angle, the main change of the flow field is the disappearance of the separation regions near the rotating cylinders and the wake region is slightly changed due to MI. In the 30\ub0 yaw angle case, the flow field is changed a lot. Large flow separations near one rotating cylinder and in the wake is significantly reduced, which results in the large drag reduction. Meanwhile, the yaw moment is increased about 50.5 %

Large eddy simulation of flow control around a cube subjected to momentum injection

The concept of Momentum Injection (MI) through Moving Surface Boundary-layer Control(MSBC) applied to a cubic structure is numerically studied using large eddy simulation at a Reynolds num-ber of 6.7 7 104 . Two small rotating cylinders are used to add the momentum at the front vertical edgesof the cube. Two configurations are studied with the yaw angle of 0◦ and 30◦ , respectively, with ratio ofthe rotation velocity of cylinders and the freestream velocity of 2. The results suggest that MI delays theboundary layer separation and reattachment, and thus reduces the drag. A drag reduction of about 6.2% isobserved in the 0◦ yaw angle case and about 45.3% reduction in the 30◦ yaw angle case. In the case of 0◦yaw angle, the main change of the flow field is the disappearance of the separation regions near the rotatingcylinders and the wake region is slightly changed due to MI. In the 30◦ yaw angle case, the flow field ischanged a lot. Large flow separations near one rotating cylinder and in the wake is significantly reduced,which results in the large drag reduction. Meanwhile, the yaw moment is increased about 44.7%

Large eddy simulation of flow control around a cube subjected to momentum injection

The concept of Momentum Injection (MI) through Moving Surface Boundary-layer Control(MSBC) applied to a cubic structure is numerically studied using large eddy simulation at a Reynolds num-ber of 6.7 7 104 . Two small rotating cylinders are used to add the momentum at the front vertical edgesof the cube. Two configurations are studied with the yaw angle of 0◦ and 30◦ , respectively, with ratio ofthe rotation velocity of cylinders and the freestream velocity of 2. The results suggest that MI delays theboundary layer separation and reattachment, and thus reduces the drag. A drag reduction of about 6.2% isobserved in the 0◦ yaw angle case and about 45.3% reduction in the 30◦ yaw angle case. In the case of 0◦yaw angle, the main change of the flow field is the disappearance of the separation regions near the rotatingcylinders and the wake region is slightly changed due to MI. In the 30◦ yaw angle case, the flow field ischanged a lot. Large flow separations near one rotating cylinder and in the wake is significantly reduced,which results in the large drag reduction. Meanwhile, the yaw moment is increased about 44.7%

An efficient Very Large Eddy Simulation model for simulation of turbulent flow

Among the various hybrid methodologies, Speziale’s very large eddy simulation (VLES) is one that wasproposed very early. It is a unified simulation approach that can change seamlessly from Reynolds AveragedNavier–Stokes (RANS) to direct numerical simulation (DNS) depending on the numerical resolution. Thepresent study proposes a new improved variant of the original VLES model. The advantages are achieved intwo ways: (i) RANS simulation can be recovered near the wall which is similar to the detached eddy simula-tion concept; (ii) a LES subgrid scale model can be reached by the introduction of a third length scale, that is,the integral turbulence length scale. Thus, the new model can provide a proper LES mode between the RANSand DNS limits. This new methodology is implemented in the standard k " model. Applications are con-ducted for the turbulent channel flow at Reynolds number of Re D 395, periodic hill flow at Re D 10, 595,and turbulent flow past a square cylinder at Re D 22, 000. In comparison with the available experimen-tal data, DNS or LES, the new VLES model produces better predictions than the original VLES model.Furthermore, it is demonstrated that the new method is quite efficient in resolving the large flow structuresand can give satisfactory predictions on a coarse mesh