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394 results on '"Xu, Jinglei"'

3. Corrected Navier-Stokes equations for compressible flows

Author

Xu, Jinglei, Ma, Dong, Liu, Pengxin, Bi, Lin, Yuan, Xianxu, and Chen, Longfei

Subjects
Physics - Fluid Dynamics, Physics - Computational Physics
Abstract

For gas flows, the Navier-Stokes (NS) equations are established by mathematically expressing conservations of mass, momentum and energy. The advantage of the NS equations over the Euler equations is that the NS equations have taken into account the viscous stress caused by the thermal motion of molecules. The viscous stress arises from applying Isaac Newton's second law to fluid motion, together with the assumption that the stress is proportional to the gradient of velocity1. Thus, the assumption is the only empirical element in the NS equations, and this is actually the reason why the NS equations perform poorly under special circumstances. For example, the NS equations cannot describe rarefied gas flows and shock structure. This work proposed a correction to the NS equations with an argument that the viscous stress is proportional to the gradient of momentum when the flow is under compression, with zero additional empirical parameters. For the first time, the NS equations have been capable of accurately solving shock structure and rarefied gas flows. In addition, even for perfect gas, the accuracy of the prediction of heat flux rate is greatly improved. The corrected NS equations can readily be used to improve the accuracy in the computation of flows with density variations which is common in nature., Comment: 13 pages, 7 figures

Published
2022

4. Lattice eddy simulation of turbulent flows

Author

Xu, Jinglei, Li, Qi, Yuan, Xianxu, Bi, Lin, Liu, Pengxin, and Chen, Jianqiang

Subjects
Physics - Fluid Dynamics
Abstract

Kolmogorov's (1941) theory of self-similarity implies the universality of small-scale eddies, and holds promise for a universal sub-grid scale model for large eddy simulation. The fact is the empirical coefficient of a typical sub-grid scale model varies from 0.1 to 0.2 in free turbulence and damps gradually to zero approaching the walls. This work has developed a Lattice Eddy Simulation method (LAES), in which the sole empirical coefficient is constant (Cs=0.08). LAES assumes the fluid properties are stored in the nodes of a typical CFD mesh, treats the nodes as lattices and makes analysis on one specific lattice, i. To be specific, LAES express the domain derivative on that lattice with the influence of nearby lattices. The lattices right next to i, which is named as i+, "collide" with i, imposing convective effects on i. The lattices right next to i+, which is named as i++, impose convective effects on i+ and indirectly influence i. The influence is actually turbulent diffusion. The derived governing equations of LAES look like the Navier-Stokes equations and reduce to filtered Naiver-Stokes equations with the Smagorinsky sub-grid scale model (Smagorinsky 1963) on meshes with isotropic cells. LAES yields accurate predictions of turbulent channel flows at Re=180, 395, and 590 on very coarse meshes and LAES with a constant Cs perform as well as the dynamic LES model (Germano et al. 1991) does. Thus, this work has provided strong evidence for Kolmogorov's theory of self-similarity., Comment: 12 pages,11 figures

Published
2022

41. Analysis of mixing enhancement ability of bypass dual throat nozzle with single/multi-tabs.

Author

Pan, Ruifeng, Xu, Jinglei, Zhang, Yuqi, Lan, Bingsong, and Huang, Shuai

Subjects
*WIND tunnels, *THROAT, *THRUST, *SPRAY nozzles
Abstract

AbstractBypass dual throat nozzle (BDTN) represents an innovative fluidic thrust vectoring nozzle capable of adjusting thrust vectoring angles through self-adaptive flow control. This study explores the BDTN-single/multi-tabs configurations, ensuring that the nozzle’s outlet projected area remains constant while introducing one or more pairs of tabs coplanar with the convergent section of the cavity. This design accounts for aerodynamic performance, thrust vectoring capabilities, and mixing abilities of the BDTN. Through theoretical analysis, design implementation, numerical simulations, and wind tunnel experiments, findings reveal that, in the case of BDTN-single-tab configuration, an increase in tab angle (α) leads to heightened streamwise vortex intensity at the nozzle outlet, reduced high-temperature core area, and enhanced jet centerline velocity and temperature attenuation rate. BDTN-single-tab achieves up to a 90% reduction in centerline-temperature/velocity decay rate, implying stronger mixing enhancement with higher tab angles. Compared to α = 10° BDTN-single-tab, the area of the high-temperature core area decays by 75%. For the BDTN-multi-tab configuration, an increase in the number of tabs results in increased thrust coefficient and vectoring angle, alongside diminished streamwise vortex strength at the nozzle outlet, and a more complex streamwise vortex structure. However, the jet’s centerline velocity and temperature decay rate decreased as a consequence. [ABSTRACT FROM AUTHOR]

Published
2024
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42. Assessment of Multi-Physical Fields Reconstruction Approaches in Three-Dimensional Supersonic Flow with Shocks.

Author

Tian, Jie, Xu, Jinglei, Zhou, Junfei, and Dong, Han

Subjects
*SUPERSONIC flow, *THREE-dimensional flow, *NAVIER-Stokes equations, *PARTICLE image velocimetry, *TRANSONIC flow, *SUBSONIC flow, *ADIABATIC flow
Abstract

AbstractThe paper evaluates the application of several multi-physical fields reconstruction approaches based on the Tomographic Particle Image Velocimetry (PIV) in three-dimensional supersonic flows with shock waves, including the pressure, temperature, and density. The MacCormack method and the Flux Vector Splitting method with outstanding performance in two-dimensional supersonic flow are extended into three-dimensional forms. The conventional Poisson method is also considered because of its widespread application and high accuracy in subsonic and transonic flow. All of these approaches are established by the conservative Navier-Stokes equations and solved by the time-marching iteration process, combined with the perfect gas law and adiabatic flow assumption. The performances are evaluated by numerical velocimetry data. To simulate the typical three-dimensional features, the cases of uniform freestream at Mach 0.78 and 3 past a cone with a 20° half-angle are selected to obtain a sufficient spanwise velocity component. The results confirm the feasibility of the PIV-based reconstruction methods in the conical flow field. The conventional Poisson method performs well only in the subsonic case while the Flux Vector Splitting method has a better performance in supersonic flow, including higher accuracy, stability, and efficiency, with a low-level root-mean-square error of 0.449% and local maximum relative error of 1%. [ABSTRACT FROM AUTHOR]

Published
2024
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