Meilin YU - Academia.edu (original) (raw)

Papers by Meilin YU

Journal of Advances in Modeling Earth Systems

• The WRF dynamic core dissipates ∼ 20% more kinetic energy than NUMA for a dry vortex forced by ... more • The WRF dynamic core dissipates ∼ 20% more kinetic energy than NUMA for a dry vortex forced by four-dimensional latent heating observations. • Values of the eddy diffusivity in WRF need to be reduced by ∼ 50% from those in NUMA in order to produce a similar intensity time series. • Budgets and sensitivity tests indicate that the low-order approximation of the pressure gradient is the source of the dissipation in WRF.

APS Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2019

A simplified flux reconstruction method, i.e., the compact direct flux reconstruction method, is ... more A simplified flux reconstruction method, i.e., the compact direct flux reconstruction method, is developed using the compact finite difference approach within the standard element. It can be regarded as a differentiation form of the direct flux reconstruction method. Implicit high-order time integration methods are employed to achieve high-order spatiotemporal accuracy and circumvent the restriction on the time step size. To efficiently solve the nonlinear and linear systems resulting from the high-order discretization, we employ the Newton--Krylov solver as well as the p-multigrid solver. Specifically, the matrix-free implementation of the generalized minimal residual method is employed to significantly reduce memory consumption. The element-Jacobi preconditioner is used for the generalized minimal residual method and it also serves as a smoother for the p-multigrid solver. The impact of the polynomial hierarchy on the convergence speed of the V-cycle p-multigrid solver is discusse...

We conduct a comparative study of the Jacobian-free linearly implicit Rosenbrock-Wanner (ROW) met... more We conduct a comparative study of the Jacobian-free linearly implicit Rosenbrock-Wanner (ROW) methods, the explicit rst stage, singly diagonally implicit Runge-Kutta (ESDIRK) methods, and the second-order backward differentiation formula (BDF2) for unsteady flow simulation using spatially high-order flux reconstruction/correction procedure via reconstruction (FR/CPR) formulations. The pseudo-transient continuation is employed to solve the nonlinear systems resulting from the temporal discretizations with ESDIRK and BDF2. A Jacobian-free implementation of the restarted generalized minimal residual method (GMRES) solver is employed with a low storage element-Jacobi preconditioner to solve linear systems, including those in linearly implicit ROW methods and those from linearization of the nonlinear systems in ESDIRK and BDF2 methods. We observe that all ROW and ESDIRK schemes (from second order to fourth order) are more computationally efficient than BDF2, and ROW methods can potential...

2018 AIAA Aerospace Sciences Meeting, 2018

The Rosenbrock-type implicit Runge-Kutta (ROIRK) methods only require one Jacobian matrix evaluat... more The Rosenbrock-type implicit Runge-Kutta (ROIRK) methods only require one Jacobian matrix evaluation per time step rather than per stage as other types of implicit Runge-Kutta (IRK) methods need. This feature makes ROIRK attractive for numerical simulations using implicit methods. We present the parallel implementation of several matrix-based ROIRK methods with flux reconstruction/correction procedure reconstruction (FR/CPR) formulations for solving the 3D Navier-Stokes equations. In this study, METIS has been utilized to partition the mesh in the preprocessing. The complex-step derivative approximation is employed to evaluate the Jacobi matrix, accurate to machine zero. The GMRES solver in the PETSc library is used to iteratively solve the linear system. The ROIRK methods have demonstrated high order of accuracy in numerical simulations. The scalability study reveals that the matrix-based ROIRK methods have good parallel efficiency. With the block Jacobi preconditioner, it is observed that the linear systems resulting from ROIRK3-3 are stiffer than those from ROIRK2-2 and ROIRK4-6. This makes the scalability of ROIRK3-3 worse than ROIRK2-2 and ROIRK4-6 taking the number of stages into account.

AIAA Scitech 2020 Forum, 2020

AIAA Aviation 2019 Forum, 2019

Energies, 2020

Vertical-axis wind turbines (VAWTs) are compact and efficient and have become increasingly popula... more Vertical-axis wind turbines (VAWTs) are compact and efficient and have become increasingly popular for wind energy harvesting. This paper mainly focuses on free and forced vibration analysis of two different types of VAWTs, i.e., an H-type VAWT and a new hybrid VAWT. The H-type VAWT has a lower cost, while the hybrid VAWT has a better self-starting capability at a low wind velocity. Both of them can be used for wind energy harvesting. By using the assumed modes method, the two VAWTs are simplified by a single degree-of-freedom (SDOF) model. By utilizing the method of structural mechanics, a multi-degree-of-freedom (MDOF) model is developed for the two VAWTs and the turbines in them are reasonably simplified. Natural frequency analyses for the SDOF and MDOF models of the two VAWTs are conducted. A beam element model (BEM) of the two VAWTs is created to calculate their natural frequencies and mode shapes and to verify natural frequency results from the SDOF and MDOF models. By using t...

2018 Fluid Dynamics Conference, 2018

55th AIAA Aerospace Sciences Meeting, 2017

Preconditioning methods can significantly decrease the condition number of the linear system resu... more Preconditioning methods can significantly decrease the condition number of the linear system resulted from the discretization of compressible Navier-Stokes equations at low Mach numbers by replacing the physical acoustic wave speeds with numerical ones. In the present study, the high-order accurate flux reconstruction/correction procedure via reconstruction (FR/CPR) method with low Mach number preconditioning is used to solve Navier-Stokes equations at low Mach numbers (M a ∼ O 10 −3). The dual time stepping method is used to handle unsteady flow simulations, wherein the second-order backward differentiation formula (BDF2) is adopted to discretize the temporal derivative with respect to the physical time. A simple modification of the preconditioning formulation is proposed to deal with dynamic meshes. Numerical results of several benchmark tests have demonstrated that the preconditioned FR/CPR method works well for low Mach number flows.

A recently developed high-order accurate flux reconstruction/correction procedure via reconstruct... more A recently developed high-order accurate flux reconstruction/correction procedure via reconstruction (FR/CPR) method equipped with localized Laplacian artificial viscosity (LLAV) shock-capturing capability is used to simulate both two dimensional (2D) and three dimensional (3D) shock-boundary layer interaction (SBLI) at different Reynolds numbers with and without wall roughness. It is found that the method can effectively and sharply resolve both shock and boundary-layer separation features. From the SBLI simulation results, it is observed that surface roughness can change the interaction between the shock waves and the boundary layers. As a result, the surface heat transfer process can be substantially modified.

arXiv: Computational Physics, 2019

The authors gratefully acknowledge the support of the Office of Naval Research through the award ... more The authors gratefully acknowledge the support of the Office of Naval Research through the award N00014-16-1-2735, and the faculty startup support from the department of mechanical engineering at the University of Maryland, Baltimore County (UMBC). The hardware used in the computational studies is part of the UMBC High Performance Computing Facility (HPCF). The facility is supported by the U.S. National Science Foundation through the MRI program (grant nos. CNS-0821258, CNS-1228778, and OAC-1726023) and the SCREMS program (grant no. DMS-0821311), with additional substantial support from UMBC.

A high-order accurate flux reconstruction/correction procedure via reconstruction (FR/CPR) method... more A high-order accurate flux reconstruction/correction procedure via reconstruction (FR/CPR) method is developed to solve incompressible Navier-Stokes equations on unstructured moving grids. An artificial compressibility method is adopted to facilitate the common flux reconstruction on element interfaces. For unsteady flow simulations, a dualtime stepping method is used for temporal discretization. For simulations on deformable/moving grids, the Geometric Conservation Law (GCL) introduced in dynamic spatial coordinate transformation has been enforced. The newly developed method is verified with several steady and unsteady benchmark incompressible flow problems.

Unsteady flow physics of two types of vertical axis wind turbines (VAWTs), namely, a modified Sav... more Unsteady flow physics of two types of vertical axis wind turbines (VAWTs), namely, a modified Savonius turbine and a hybrid Darrieus-modified-Savonius (HDMS) turbine, are numerically studied using a fluid-structure interaction approach. As a first step, a numerical solver is developed by coupling the wind turbine dynamics with a high-fidelity flow solver, thus, synchronizing the flow-turbine interaction. The solver is then used to study unsteady aerodynamics of wind-driven modified Savonius and HDMS VAWTs under different loading conditions. The relationship between the power efficiency and tip speed ratio (TSR) is invested for both types of wind turbines. It is found that there exists large disparity on energy harvesting performance between the two types of VAWTs under wind-driven flow conditions. The modified Savonius VAWT achieves relatively high power efficiency (~30% or ~51% of the Betz's limit) at small TSRs; the HDMS VAWT achieves high power efficiency (~40% or ~67% of the Betz's limit) at large TSRs. At the same incoming wind speed, the maximum power efficiency of the HDMS VAWT is about 10% higher than that of the Savonius VAWT. It is also observed that the external loading can affect dynamic stall over Darrieus blades of the HDMS VAWT, thus significantly varying the TSR and the corresponding energy harvesting efficiency.

Experimental and numerical studies have been performed to investigate the performance of a vertic... more Experimental and numerical studies have been performed to investigate the performance of a vertical gust generator in a wind tunnel. Results from both experimental Particle Image Velocimetry (PIV) and those from numerical simulations of low-Mach-numberpreconditioned compressible Naiver-Stokes equations on unstructured grids using high-order spectral difference (SD) agreed reasonably well with each other. The gust was generated by ducting flow through the floor of the wind tunnel and at the wall of the numerical domain. The gust velocity profile bends downstream when interacting with freestream causing the incoming freestream flow to bend upward. The vertical gust changed the effective angle of attack over the airfoil when interacting with the freestream velocity. Due to the interaction of gust over the airfoil, the stationary airfoil at a nominal zero degree angle of attack undergo flow separation under stalled conditions.

Wang and Yu gratefully acknowledge the support of the Office of Naval Research through the award ... more Wang and Yu gratefully acknowledge the support of the Office of Naval Research through the award N00014–16–1–2735, and the faculty startup support from the department of mechanical engineering at University of Maryland, Baltimore County (UMBC). The hardware used in the computational studies is part of the UMBC High Performance Computing Facility (HPCF). The facility is supported by the U.S. National Science Foundation through the MRI program (grant nos. CNS–0821258 and CNS–1228778) and the SCREMS program (grant no. DMS–0821311), with additional substantial support from the University of Maryland, Baltimore County (UMBC). See hpcf.umbc.edu for more information on HPCF and the projects using its resources.

AIAA Scitech 2019 Forum, 2019

This paper presents the development of a high-order flux reconstruction (FR) formulation for unst... more This paper presents the development of a high-order flux reconstruction (FR) formulation for unsteady flow simulation with dynamic grid algorithms. Specifically, the high-order FR formulation for the Navier-Stokes equations in an arbitrary Lagrangian-Eulerian (ALE) format is developed for numerical simulation on moving domains. A hybrid moving grid algorithm consisting of algebraic grid smoothing and grid regeneration methods is developed to resolve domains with large deformation. The 'dist-mesh' technique is used for mesh regeneration, and local Lagrange interpolation within finite elements is used for flow field reconstruction. Several unsteady flow cases are studied to verify the effectiveness of the new method developed in this work.