Search

In this paper, a novel adaptive central-upwind WCNS (weighted compact nonlinear scheme) based on an adjusting parameter of smoothness indicator is proposed. For the purpose of restraining numerical dissipation in smooth regions, avoiding spurious numerical oscillations dramatically, and preserving shock-capturing ability around discontinuity regions, an adaptive parameter is introduced in this modified WCNS scheme. Based on the above improvement, nonlinear weights could automatically fit discontinuity according to the local flow-field properties obtained by a discontinuity detector. In smooth regions, it is inclined toward optimal central scheme to minimize dissipations and capture turbulent features, while, in discontinuity regions, it is more likely inclined toward upwind scheme for stable shock-capturing ability and numerical robustness. Furthermore, to solve the problem of losing accuracy, the smoothness indicator with a mapping function is introduced. A variety of benchmark-test cases are tested to verify the modified WCNS scheme performance. Numerical results demonstrate that, compared with the EWENO-CU4 scheme, the modified WCNS scheme exhibits excellent shock-capturing ability, lower numerical dissipation, and higher numerical robustness in resolving complex flow features.

Direct numerical simulations were conducted to investigate physical structures of a transverse sonic air jet injected into a supersonic air crossflow at a Mach number of 2.7. Simulations were run for two different jet-to-crossflow momentum flux ratios (J) of 1.85 and 5.5. The main averaged flow features around the transverse jet, such as major counter rotating vortices (CRVs) and trailing CRVs (TCRVs) were captured. The major CRVs form in the lateral portion of the jet plume and absorb other induced trailing vortices downstream of the jet plume. Upper trailing CRVs form above the major CRVs downstream of the jet barrel shock. The streamline analysis indicates that the upper trailing CRVs are related to the Mach disk. As the streamlines penetrate the lateral side of Mach disk where a strong shear condition exists, the baroclinic torque induces upper vorticities in the opposite rotating direction against the major CRVs. Downstream of the Mach disk, the baroclinic vorticity production along the streamlines tends to approach zero, which means no more torque is pumped into the farfield and the upper TCRVs are merged into the major CRVs by their suction.

Using the particle-based laser scattering imaging technique, schlieren system and surface oil-flow visualization technique, the flow patterns and mixing characteristics of multiple injections with tandem multi-orifices and parallel multi-orifices in a supersonic vitiated air flow were investigated in this paper. All injectors have a declined angle of 30 degree to the freestream direction. The distance between the tandem orifices and that between the parallel orifices was varied. The experimental results showed that decreasing the distance between the tandem orifices will reduce the pressure and velocity of the stream upstream of the second jet, which results in the increase of the penetration height of the second injection and quick mixing of the whole field. For the small distance between the parallel multi-orifices, the bow shock waves upstream of the injected jets connect with each other and the air stream entered into the gap between the jets is not enough, resulting in the decrease of the mixing effect. Large distance between the parallel multi-orifices decreases the interaction between the injection jets. For the mixing enhancement, there should be a proper optimized distance between the parallel injection orifices.