Development of high-order TENO schemes by Lin Fu

Equilibrium wall-modeled LES of shock-induced aerodynamic heating in hypersonic boundary layers

In this study, equilibrium WMLES has been compared against DNS for addressing the performance of the former in predicting shock-induced transition and heating in hypersonic boundary layers. In this flow, the equilibrium wall model underperforms in a number of different metrics. At low shock-incidence angles, the post-shock boundary layer in DNS is laminar, whereas it rapidly transitions to turbulence in WMLES. At higher incidence angles, both DNS and WMLES predict transition under no inflow disturbances, with WMLES results agreeing qualitatively with the overall trends in DNS. However, from a quantitative standpoint, WMLES underpredicts all of the following: (a) the size of the separation bubble by a factor of 2; (b) the post-shock peak skin friction by up to 30%; and (c) the post-shock peak aerodynamic heating rate by up to 30%. Overall, the considerations above suggest that upgraded wall models beyond the equilibrium one may be required to predict these phenomena.

A hybrid method with TENO based discontinuity indicator for hyperbolic conservation laws

With the observation that the TENO weighting strategy can explicitly distinguish smooth scales from nonsmooth scales in spectral space, in this paper, a new discontinuity indicator is proposed based on the high-order TENO paradigm [Fu et al., JCP 305(2016) : 333-359]. The local flow structures are classified as smooth or nonsmooth scales, and the hybrid numerical discretization scheme is applied correspondingly, i.e. the high-order upwind linear scheme without characteristic decomposition is employed for resolving smooth scales while the nonlinear low-dissipation TENO scheme is adopted to capture discontinuities. Since the time-consuming characteristic decomposition and smoothness-indicator computation of TENO are avoided in smooth regions, the overall computational efficiency can be improved significantly. Moreover, the cut-off wavenumber separating smooth and nonsmooth scales is determined by the parameter CT. In contrast to the thresholds of other discontinuity indicators, which are typically defined in physical space, CT takes effects in wavespace rendering its high generality. A set of benchmark cases with widespread length-scales is simulated to assess the performance of the proposed discontinuity indicator and the resulting hybrid shock-capturing scheme. Compared to the monotonicity-preserving discontinuity indicator and the TVB discontinuity indicator, the proposed algorithm delivers better performance with a fixed set of parameters for all considered benchmarks.

Parallel fast-neighbor-searching and communication strategy for particle-based methods

We develop a parallel fast neighbor search method and communication strategy for particle-based methods with adaptive smoothing-length on distributed-memory computing systems. With a multi-resolution based hierarchical data structure, the parallel neighbor search method is developed to detect and construct ghost buffer particles, i.e. neighboring particles on remote processor nodes. In order to migrate ghost buffer particles among processor nodes, an undirected graph is established to characterize the sparse data communication relation and is dynamically recomposed. By the introduction of an edge coloring algorithm from graph theory, the complex sparse data exchange can be accomplished within optimized frequency. For each communication substep, only efficient nonblocking point-to-point communication is involved. We consider two demonstration scenarios: (i) fluid dynamics based on smoothed-particle hydrodynamics with adaptive smoothing-length, (ii) a recently proposed physics-motivated partitioning method [Fu et al., JCP 341 (2017): 447-473]. Several new concepts are introduced to recast the partitioning method into a parallel version. A set of numerical experiments is conducted to demonstrate the performance and potential of the proposed parallel algorithms. The proposed methods are simple to implement in large-scale parallel environment and can handle particle simulations with arbitrarily varying smoothing-lengths. The implemented SPH solver has good parallel performance, suggesting the potential for other scientific applications.