scholarly journals Quasi-three-dimensional numerical model for flow through flexible, rigid, submerged and non-submerged vegetation

2003 ◽  
Vol 5 (3) ◽  
pp. 189-202 ◽  
Author(s):  
K. S. Erduran ◽  
V. Kutija
Keyword(s):  
Eddy Viscosity ◽  
Stokes Equations ◽  
Correction Term ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Beam Theory ◽  
Shear Stresses ◽  
Complex Flow ◽  
Drag Forces ◽  
Major Interest

The effects of the resistance caused by vegetation on flow velocity and water depth has become a major interest for ecologists and those who deal with river restoration projects. Some numerical and experimental works have been performed to analyse and formulate the drag effects induced by vegetation. Here we introduce a quasi-three-dimensional (Q3D) numerical solution, which is constructed by coupling the finite volume solution of the two-dimensional shallow water equations with a finite difference solution of Navier–Stokes equations for vertical velocity distribution. The drag forces are included in both sets of equations. Turbulence shear stresses are computed in two alternative ways: the parabolic eddy viscosity approach with a correction term introduced in this study, and a combination of the eddy viscosity and mixing length theories in the vertical direction. In order to deal with flexible vegetation, a cantilever beam theory is used to compute the deflection of the vegetation. The model COMSIM (complex flow simulations) has been developed and applied in experimental cases. The results are shown to be satisfactory.

scholarly journals A Multi-GPU Parallel Algorithm in Hypersonic Flow Computations

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Jianqi Lai ◽  
Hua Li ◽  
Zhengyu Tian ◽  
Ye Zhang
Keyword(s):  
Parallel Algorithm ◽  
Hypersonic Flow ◽  
Stokes Equations ◽  
Programming Model ◽  
Graphics Processing Unit ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Time Discretization ◽  
Processing Unit ◽  
Complex Flow

Computational fluid dynamics (CFD) plays an important role in the optimal design of aircraft and the analysis of complex flow mechanisms in the aerospace domain. The graphics processing unit (GPU) has a strong floating-point operation capability and a high memory bandwidth in data parallelism, which brings great opportunities for CFD. A cell-centred finite volume method is applied to solve three-dimensional compressible Navier–Stokes equations on structured meshes with an upwind AUSM+UP numerical scheme for space discretization, and four-stage Runge–Kutta method is used for time discretization. Compute unified device architecture (CUDA) is used as a parallel computing platform and programming model for GPUs, which reduces the complexity of programming. The main purpose of this paper is to design an extremely efficient multi-GPU parallel algorithm based on MPI+CUDA to study the hypersonic flow characteristics. Solutions of hypersonic flow over an aerospace plane model are provided at different Mach numbers. The agreement between numerical computations and experimental measurements is favourable. Acceleration performance of the parallel platform is studied with single GPU, two GPUs, and four GPUs. For single GPU implementation, the speedup reaches 63 for the coarser mesh and 78 for the finest mesh. GPUs are better suited for compute-intensive tasks than traditional CPUs. For multi-GPU parallelization, the speedup of four GPUs reaches 77 for the coarser mesh and 147 for the finest mesh; this is far greater than the acceleration achieved by single GPU and two GPUs. It is prospective to apply the multi-GPU parallel algorithm to hypersonic flow computations.

scholarly journals Development of an Aerostructural Analysis Tool for a Low-Sweep Parametric Wing

2021 ◽  
Author(s):  
Julian Bardin
Keyword(s):  
Boundary Layer ◽  
Direct Method ◽  
Three Dimensional ◽  
Beam Theory ◽  
Leading Edge ◽  
Analysis Tool ◽  
Two Dimensional ◽  
Viscous Boundary Layer ◽  
Drag Forces ◽  
Displacement Thickness

An aerostructural analysis program was developed to predict the aerodynamic performance of a non-rigid, low-sweep wing. The wing planform was geometrically defined to have a rectangular section, and a trapezoidal section. The cross-section was further set to an airfoil shape which was consistent across the entire wingspan. Furthermore, to enable the inclusion of this multidisciplinary analysis module into an optimization scheme, the wing geometry was defined by a series of parameters: root chord, taper ratio, leading-edge sweep, semi-span length, and the kink location. Aerodynamic analysis was implemented through the quasi-three-dimensional approach, including a three-dimensional inviscid solution and a sectional two-dimensional viscous solution. The inviscid analysis was provided through the implementation of the vortex ring lifting surface method, which modelled the wing about its mean camber surface. The viscous aerodynamic solution was implemented through a sectional slicing of the wing. For each section, the effective angle of attack was determined and provided as an input to a two-dimensional airfoil solver. This airfoil solution was comprised of two subcomponents: a linear-strength vortex method inviscid solution, and a direct-method viscous boundary layer computation. The converged airfoil solution was developed by adjusting the effective airfoil geometry to account for the boundary layer displacement thickness, which in itself required the inviscid tangential speeds to compute. The structural solution was implemented through classical beam theory, with a torsion and bending calculator included. The torque and bending moment distribution along the wing were computed from the lift distribution, neglecting the effects of drag, and used to compute the twist and deflection of the wing. Interdisciplinary coupling was achieved through an iterative scheme. With the developed implementation, the inviscid lift loads were used to compute the deformation of the wing. This deformation was used to update the wing mesh, and the inviscid analysis was run again. This iteration was continued until the lift variation between computations was below 0.1%. Once the solution was converged upon by the inviscid and structural solutions, the viscous calculator was run to develop the parasitic drag forces. Once computation had completed, the aerodynamic lift and drag forces were output to mark the completion of execution.

Assessing the Disturbed Flow and the Transition to Turbulence in the Arteriovenous Fistula

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Simone Stella ◽  
Christian Vergara ◽  
Luca Giovannacci ◽  
Alfio Quarteroni ◽  
Giorgio Prouse
Keyword(s):  
Velocity Field ◽  
Arteriovenous Fistula ◽  
Stokes Equations ◽  
Computational Study ◽  
Color Doppler ◽  
Three Dimensional ◽  
Transition To Turbulence ◽  
Shear Stresses ◽  
Angle Of Incidence ◽  
Disturbed Flow

The arteriovenous fistula (AVF) is the main form of vascular access for hemodialysis patients, but its maintenance is very challenging. Its failure is mainly related to intimal hyperplasia (IH), leading to stenosis. The aim of this work was twofold: (i) to perform a computational study for the comparison of the disturbed blood dynamics in different configurations of AVF and (ii) to assess the amount of transition to turbulence developed by the specific geometric configuration of AVF. For this aim, we reconstructed realistic three-dimensional (3D) geometries of two patients with a side-to-end AVF, performing a parametric study by changing the angle of incidence at the anastomosis. We solved the incompressible Navier–Stokes equations modeling the blood as an incompressible and Newtonian fluid. Large eddy simulations (LES) were considered to capture the transition to turbulence developed at the anastomosis. The values of prescribed boundary conditions are obtained from clinical echo-color Doppler (ECD) measurements. To assess the disturbed flow, we considered hemodynamic quantities such as the velocity field, the pressure distribution, and wall shear stresses (WSS) derived quantities, whereas to quantify the transition to turbulence, we computed the standard deviation of the velocity field among different heartbeats and the turbulent kinetic energy.

Numerical exploration on drag and heat reduction mechanism of a spike-tipped supersonic blunt nose

2020 ◽  
Vol 34 (32) ◽  
pp. 2050370
Author(s):  
Yu-Shan Meng ◽  
Li Yan ◽  
Shi-Bin Li ◽  
Wei Huang
Keyword(s):  
Heat Flux ◽  
Drag Force ◽  
Stokes Equations ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Viscous Force ◽  
Reduction Mechanism ◽  
Complex Flow ◽  
Drag Ratio ◽  
Lift To Drag Ratio

In this study, the drag force and heat flux reduction mechanism induced by the aerodisk (with disks on its nose) with the freestream Mach number being 4.937 has been numerically investigated, and the simulations have been carried out by the three-dimensional Reynolds-averaged Navier–Stokes equations coupled with the SST [Formula: see text] turbulence model. The influence of the angle of attack on the drag and heat flux reduction has been analyzed comprehensively. The obtained results show that the drag force of the spiked blunt body can be reduced by the aerodisk, and the drag force decreases by 24.63%. The flow mechanism of the complex flow is drastically modified by the angle of attack, and this results in a strong flow asymmetry. This asymmetry becomes more and more obvious as the angle of attack increases. Both the pressure force and viscous force increase with the increase of the angle of attack. Moreover, both the lift and drag coefficients increase as the angle of attack increases, and the lift-to-drag ratio increases first and then decreases with the increase of the angle of attack. When the angle of attack is [Formula: see text], the maximum lift-to-drag ratio is close to 0.36.

Solar Radiation Thruster Performance Analysis With Energy Storage in Porous Material

1999 ◽  
Author(s):  
Yen-Sen Chen ◽  
Jiwen Liu ◽  
Hong Wei
Keyword(s):  
Fluid Dynamics ◽  
Stokes Equations ◽  
Numerical Models ◽  
Rocket Engine ◽  
Three Dimensional ◽  
Engine Performance ◽  
Physical Models ◽  
Curvilinear Coordinates ◽  
Design Parameters ◽  
Drag Forces

Abstract The objective of this study is to develop analytical codes to support the design effort of the Shooting Star Flight Experiment’s rocket engine. Numerical models can augment the design effort by providing insight into fluid dynamics issues. Then, the design team can utilize the developed code to assess the design parameters and the engine performance as well as other issues related to thermal propulsion. The physical models developed in this study are: (a) a radiation model based on a GRASP code for general multi-block curvilinear coordinates and with a time accurate Crank-Nicholson marching scheme for heat conduction to model the absorber component of the engine; and (b) a fluid dynamics computational model using the Navier-Stokes equations, porosity factors and drag forces terms for simple one-dimensional simulations to complete three-dimensional modeling of the Shooting Star Engine internal flows.

Examining the Aerodynamic Drag and Lift Characteristics of a Newly Developed Elliptical-Bladed Savonius Rotor

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Nur Alom ◽  
Ujjwal K. Saha
Keyword(s):  
Wind Tunnel ◽  
Stokes Equations ◽  
Aerodynamic Drag ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Wind Tunnel Experiments ◽  
Drag Forces ◽  
Velocity Magnitude ◽  
Bladed Rotor ◽  
Drag And Lift

The elliptical-bladed Savonius wind turbine rotor has become a subject of interest because of its better energy capturing capability. Hitherto, the basic parameters of this rotor such as overlap ratio, aspect ratio, and number of blades have been studied and optimized numerically. Most of these studies estimated the torque and power coefficients (CT and CP) at given flow conditions. However, the two important aerodynamic forces, viz., the lift and the drag, acting on the elliptical-bladed rotor have not been studied. This calls for a deeper investigation into the effect of these forces on the rotor performance to arrive at a suitable design configuration. In view of this, at the outset, two-dimensional (2D) unsteady simulations are conducted to find the instantaneous lift and drag forces acting on an elliptical-bladed rotor at a Reynolds number (Re) = 0.892 × 105. The shear stress transport (SST) k–ω turbulence model is used for solving the unsteady Reynolds averaged Navier–Stokes equations. The three-dimensional (3D) unsteady simulations are then performed which are then followed by the wind tunnel experiments. The drag and lift coefficients (CD and CL) are analyzed for 0–360 deg rotation of rotor with an increment of 1 deg. The total pressure, velocity magnitude, and turbulence intensity contours are obtained at various angles of rotor rotation. For the elliptical-bladed rotor, the average CD, CL, and CP, from 3D simulation, are found to be 1.31, 0.48, and 0.26, respectively. The average CP for the 2D elliptical profile is found to be 0.34, whereas the wind tunnel experiments demonstrate CP to be 0.19.

scholarly journals SURPRISING BEHAVIOUR AND SINGULARITY IN THE SAINT VENANT APPROXIMATION FOR A FLUID

2018 ◽  
Author(s):  
Paolo Luchini
Keyword(s):  
Numerical Simulation ◽  
Eddy Viscosity ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Venant Equation ◽  
Change Of Perspective ◽  
The Subject ◽  
Substantial Change

A research line is reviewed which, over a few years, led to a substantial change of perspective about the simplified models that underlie the description of quasi-onedimensional streams, their instabilities, and their effects upon sandy beds. Even when the flow is assumed to be laminar, the Saint-Venant equation of quasi-onedimensional fluid flow can be formulated in more than one manner; it will be shown that only one of these choices is consistent with the complete three-dimensional Navier- Stokes equations. When the flow is turbulent, an added complication is the presence of a turbulence model, most often of the eddy-viscosity type; it will be shown that such a model can be in strong contrast with a direct numerical simulation of the same phenomenon, even to the point of producing results of opposite sign. In addition, the complete numerical simulation of flow past an undulated bottom exhibits a non-monotonic approach to its long-wave, quasi-onedimensional limit, with a surprising resonance that has no laminar counterpart and must become the subject of future investigations.

High Fidelity Simulation of Safety Relief Valve Internal Flows

2015 ◽  
Author(s):  
Yunchao Yang ◽  
Alexis Lefebvre ◽  
Ge-Cheng Zha ◽  
Qing-Feng Liu ◽  
Jun Fan ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Complex Geometry ◽  
Three Dimensional ◽  
Weno Scheme ◽  
Inlet Pressure ◽  
Navier Stokes ◽  
Implicit Time ◽  
Complex Flow ◽  
Relief Valve ◽  
Expansion Waves

This paper presents a numerical methodology and simulation for three-dimensional transonic flow in Safety Relief Valves. Simulation of safety relief valve flows is very challenging due to complex flow paths, high pressure variation, supersonic flow with shock and expansion waves, boundary layers, etc. The 3D unsteady Reynolds averaged Navier-Stokes (URANS) equations with one-equation Spalart-Allmaras turbulence model is used. A fifth order WENO scheme for the inviscid flux and a second order central differencing for the viscous terms are employed to discretize the Navier-Stokes equations. The low diffusion E-CUSP scheme used as the approximate Riemann solver suggested by Zha et al. is utilized with the WENO scheme to evaluate the inviscid fluxes. Implicit time marching method with 2nd order temporal accuracy using Gauss-Seidel line relaxation is employed to achieve a fast convergence rate. Parallel computing is implemented to save wall clock simulation time. The valve flows with air under different inlet pressures and temperatures are successfully simulated for the full geometry with all the fine leakage channels. A 3D mesh topology is generated for the complex geometry. Detailed simulations of air flow are accomplished with inlet gauge pressure 0.5MPa and 2.1MPa. The simulated air mass flow rate agrees excellently with the experimental results with an error of 0.26% for the inlet pressure of 0.5Mpa, and an error of 2.5% for the inlet pressure of 2.1MPa. The shock waves and expansion waves downstream of the orifice are very well resolved.

Numerical study of three-dimensional Kolmogorov flow at high Reynolds numbers

1996 ◽  
Vol 306 ◽  
pp. 293-323 ◽  
Author(s):  
Vadim Borue ◽  
Steven A. Orszag
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Large Reynolds Number ◽  
Kolmogorov Flow ◽  
Turbulence Decay ◽  
High Reynolds

High-resolution numerical simulations (with up to 2563 modes) are performed for three-dimensional flow driven by the large-scale constant force fy = F cos(x) in a periodic box of size L = 2π (Kolmogorov flow). High Reynolds number is attained by solving the Navier-Stokes equations with hyperviscosity (-1)h+1Δh (h = 8). It is shown that the mean velocity profile of Kolmogorov flow is nearly independent of Reynolds number and has the ‘laminar’ form vy = V cos(x) with a nearly constant eddy viscosity. Nevertheless, the flow is highly turbulent and intermittent even at large scales. The turbulent intensities, energy dissipation rate and various terms in the energy balance equation have the simple coordinate dependence a + b cos(2x) (with a, b constants). This makes Kolmogorov flow a good model to explore the applicability of turbulence transport approximations in open time-dependent flows. It turns out that the standard expression for effective (eddy) viscosity used in K-[Escr ] transport models overpredicts the effective viscosity in regions of high shear rate and should be modified to account for the non-equilibrium character of the flow. Also at large scales the flow is anisotropic but for large Reynolds number the flow is isotropic at small scales. The important problem of local isotropy is systematically studied by measuring longitudinal and transverse components of the energy spectra and crosscorrelation spectra of velocities and velocity-pressure-gradient spectra. Cross-spectra which should vanish in the case of isotropic turbulence decay only algebraically but somewhat faster than corresponding isotropic correlations. It is verified that the pressure plays a crucial role in making the flow locally isotropic. It is demonstrated that anisotropic large-scale flow may be considered locally isotropic at scales which are approximately ten times smaller than the scale of the flow.

Experimental and Numerical Analysis of Compressor Inlet Volutes

1997 ◽  
Author(s):  
V. Michelassi ◽  
M. Giachi
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Computer Code ◽  
Navier Stokes ◽  
Complex Flow ◽  
Flow Distortion ◽  
Navier Stokes Equations ◽  
Flow Angle ◽  
Compressor Impeller ◽  
Compressor Inlet

A typical compressor inlet volute is studied by using both experimental and numerical approaches. The highly distorted and complex flow pattern is measured in two typical configurations. Measurements include velocity, flow angle, Mach number and losses. The same geometries are analyzed by using a computer code which solves the three-dimensional Navier-Stokes equations. Turbulence effects are modeled by a two-equation turbulence model. The set of measurements shows the flow distortion induced by the volute, and also highlights how this distortion can be controlled or largely reduced by small modifications to the geometry. The computational results indicate an overall good agreement with the measurements and allow reproducing the changes in the pattern induced by the changes in volute geometry. Both the measurements and computations prove the importance of the optimal design of this component which controls the uniformity of the flow approaching the compressor impeller.

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