Enabling Technologies in the Problem Solving Environment HEDP

Enabling technologies are those technologies preparing input data,analyzing output data and facilitating the whole processes for numerical simulations.This paper outlines current enabling technologies for large-scale multidisciplinary simulations used in the High End Digital Prototyping(HEDP)system,a problem solving environment equipped with capability of mesh generation and large-scale visualization.A problem solving environment is a computer system that provides all the computational facilities necessary to solve a target class of problems.Mesh generation continues to be the pacing technology for a practical numerical analysis,which is essential to yielding an accurate and efficient solution.Large-scale visualization maps the massive data to some kinds of scenes interactively,which can be realized through a tiled display wall system with distributed visualization capability.HEDP is designed for large-scale andmultidisciplinary simulations,and there are four categories of modules involved,namely pre-processing module,computing module,post-processing module,and platform control module.All these modules are coupled through a software bus,which makes the modules integrated seamlessly.Detailed design principles and applications of the HEDP environment are addressed in this paper.

Effects of temperature on drag reduction in a subsonic turbulent boundary layer via micro-blowing array

A comparative study of two micro-blowing temperature cases has been performed to investigate the characteristics of drag reduction in a subsonic flat-plate flow(where the freestream Mach number is 0.7) by means of Direct Numerical Simulation(DNS). With minute amount of blowing gas injected from a 32 × 32 array of micro-holes arranged in a staggered pattern, the porosity of micro-holes is 23% and the blowing coefficient is 0.125%. The simulation results show that a drag reduction is achieved by micro-blowing, and a lower wall-friction drag can be obtained at a higher blowing temperature. The role of micro-blowing is to redistribute the total kinetic energy in the boundary layer, and the proportion of stream-wise kinetic energy decreases, resulting in the thickened boundary layer. Increasing micro-blowing temperature can accelerate this process and obtain an enhanced drag reduction. Moreover, an explanation of drag reduction by microblowing related to the micro-jet vortex clusters is proposed that these micro-jet vortex clusters firmly attached to the wall constitute a stable barrier, which is to prevent the direct contact between the stream-wise vortex and the wall. By Dynamic Mode Decomposition(DMD) from temporal/spatial aspects, it is revealed that small structures in the near-wall region play vital role in the change of turbulent scales. The high-frequency patterns are clearly strengthened, and the lowfrequency patterns just maintain but are lifted up.

Mesh Adaptation for Curing the Pathological Behaviors of an Upwind Scheme

In present paper,mesh adaptation is applied for curing the pathological behaviors of the enhanced time-accurate upwind scheme(Loh&Jorgenson,AIAAJ 2016).In the original ETAU(enhanced time-accurate upwind)scheme,a multidimensional dissipation model is required to cure the pathological behaviors.The multi-dimensional dissipation model will increase the global dissipation level reducing numerical resolution.In present work,the metric-based mesh adaptation strategy provides an alternative way to cure the pathological behaviors of the shock capturing.The Hessian matrix of flow variables is applied to construct the metric,which represents the curvature of the physical solution.The adapting operation can well refine the anisotropic meshes at the location with large gradients.The numerical results show that the adaptation of mesh provides a possible way to cure the pathological behaviors of upwind schemes.

Numerical analysis of turbulence characteristics in a flat-plate flow with riblets control

A comparative study about riblets-controlled turbulent boundary layers has been performed to investigate the turbulence characteristics associated with drag reduction in a compressive flat-plate flow(where the free-stream Mach number is 0.7)by means of direct numerical simulations(DNSs).With a setting of the triangular riblets(s+≈30.82,h+≈15.41)settled on the Reτ≈500 turbulent boundary layer,an effective global drag reduction was achieved.By comparing velocity and its fluctuation distribution,vorticity fluctuation and streaks structures between the smooth and riblets flat-plate cases,two roles of lifting and rectification in terms of riblets drag control are revealed that the micro-scale riblets can lift up logarithmic-law region of the boundary layer,which leads to a smaller wall friction velocity and thus a drag reduction.The streamwise vortices and its fluctuation structures are shifted upward,thus the interactions between them and the wall surface are weakened,which causes the suppressed intensity of Reynolds normal stresses,streamwise vorticity and turbulent kinetic energy production inside the riblets.Moreover,the streaks associated with streamwise velocity or 3D vortices are ruled from the distorted to long and straight structures as they pass through the riblets,indicating an ability of riblets to turn turbulence into a more ordered state.