Engineering topics
Publications and source records attributed to Shih, S. H..
In this work, a new optimized MacCormack-type scheme, which is 4th order accurate in time and space, is applied to Problems 1 and 2 of Category 1. The performance of this new scheme is compared to that of the 2-4 MacCormack scheme, and results for Problems 1 and 2 of Category 1 are presented and compared to the exact solutions.
A zonal approach for direct computation of sound generation and propagation from a supersonic jet is investigated. The present work splits the computational domain into a nonlinear, acoustic-source regime and a linear acoustic wave propagation regime. In the nonlinear regime, the unsteady flow is governed by the large-scale equations, which are the filtered compressible Navier-Stokes equations. In the linear acoustic regime, the sound wave propagation is described by the linearized Euler equations. Computational results are presented for a supersonic jet at M = 2. 1. It is demonstrated that no spurious modes are generated in the matching region and the computational expense is reduced substantially as opposed to fully large-scale simulation.
The unsteady structure of a supersonic jet is highly three dimensional, though the mean flow is axisymmetric. In simulating a circular jet, the centerline represents a computational boundary. As such, spurious modes can be generated near centerline, unless special attention is given to the behavior of the 3D structure near the centerline. Improper treatment of the dependent variables near the centerline results in the solution diverging or being suitable only for small amplitude excitation. With a careful treatment of the centerline formation, no spurious mode is generated. The results show that a near-linear disturbance growth is obtained, as the linear stability theory indicates. At high levels of excitation, nonlinear development of disturbances is evident and saturation is reached downstream.
Jet noise is directly predicted using large-scale equations. The computational domain is extended in order to directly capture the radiated field. As in conventional large-eddy-simulations, the effect of the unresolved scales on the resolved ones is accounted for. Special attention is given to boundary treatment to avoid spurious modes that can render the computed fluctuations totally unacceptable. Results are presented for a supersonic jet at Mach number 2.1.
Flow-field characteristics are simulated numerically in an oblique shock wave/turbulent boundary layer interactions with six different bleed slot configurations. The strong conservation-law form of the 2D compressible Navier-Stokes equations and the k-epsilon equations are solved throughout the interaction region and inside the bleed slot. The computed results are presented for a normal and 20-deg slanted bleed slots at three different locations, upstream, across and downstream of the impingement point of an oblique shock of sufficient strength to cause boundary layer separation without bleed. The detailed flow characteristics in the interaction zone and inside the bleed slot are compared for the different bleed slot configurations. The resulting surface pressure and shear stress distributions as well as the boundary layer characteristics downstream of the interaction region are also presented for the mix bleed configurations at different bleed mass flows up to choking.
A numerical investigation was conducted to study the effect of bleed configuration on oblique-shock wave/turbulent boundary-layer interactions. Bleed is applied through a normal slot across the shock impingement location. The numerical solution to the compressible Navier-Stokes equations is obtained for the turbulent flow throughout the interaction zone and inside the bleed slot for bleed mass flow rates up to 57 percent of the boundary layer mass flow upstream of the interaction. The results indicate that the bleed slot performance improves as the slot width decreases and the length to width ratio increases. This is reflected as an increase in the bleed discharge coefficient and total pressure, and a reduction in the boundary layer momentum and displacement thickness downstream.
A numerical investigation was conducted to determine the effect of bleed on oblique shock wave/turbulent boundary layer interactions. The numerical solution to the compressible Navier-Stokes equations reveal the flow details throughout the interaction zone and inside the normal bleed slot. Results are presented for an incident oblique shock of sufficient strength to cause boundary layer separation in the absence of bleed. Bleed is applied across the shock impingement location over a range of bleed mass flow rates corresponding to different values of plenum pressures. The results indicate a complex flow structure with large variations in both normal and tangential flow velocities across the bleed slot. The flow entrainment into the slot is accompanied by an expansion-compression wave system with a bow shock originating inside the bleed slot. Increasing the bleed mass flow by decreasing the plenum pressure caused an initial decrease then a later increase in the boundary layer momentum and displacement thickness downstream of the interaction.