Numerical investigation of secondary flows in a constant-width wind-tunnel contraction

2015 ◽  
Vol 119 (1215) ◽  
pp. 613-630 ◽  
Author(s):  
M. Bouriga ◽  
R. Taher ◽  
F. Morency ◽  
J. Weiss
Keyword(s):  
Wind Tunnel ◽  
Boundary Layers ◽  
Stokes Equations ◽  
Constant Width ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Longitudinal Vortices ◽  
Dimensional Boundary

AbstractThe flow inside a constant-width wind-tunnel contraction is simulated by solving the Reynolds-Averaged Navier-Stokes equations with an eddy-viscosity turbulence model. The results show the presence of longitudinal vortices near the sidewalls centreline. This confirms a former hypothesis involving the generation of skew-induced longitudinal vorticity within the sidewalls boundary layers. Detailed analysis reveals that the flow structure is influenced by viscous effects in the boundary layers and streamline curvature in the potential flow. Three-dimensional boundary-layer profiles on the contraction sidewall are analysed in the framework of the streamline co-ordinate system and its associated hodographic diagram. The resulting profiles help understand the generation of secondary flows and the associated longitudinal vorticity.

A reversed-flow singularity in interacting boundary layers

1988 ◽  
Vol 420 (1858) ◽  
pp. 21-52 ◽  
Keyword(s):  
Critical Point ◽  
Skin Friction ◽  
Boundary Layers ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Reversed Flow ◽  
Local Pressure ◽  
Widespread Application ◽  
Limit Value ◽  
Dimensional Boundary

It is proposed that a singularity can occur in interacting boundary layers when reversed flow is present. The theoretical breakdown/singularity takes place in general at a critical point between separation and reattachment and it involves viscous-inviscid interaction between the sublayers that develop on either side of the critical point, because of a streamfunction behaviour like normal distance to the power K near the wall and possibly in mid-eddy. Moreover, the breakdown is for a value of the controlling parameter not much beyond the value that first produces separation. A study of the acceptable K range tends to suggest that the singularity arises either for the value K = 3/2, corresponding to the local pressure gradient and skin friction being singular like streamwise distance to the powers -3/5 and -1/5 respectively, subject to logarithmic modifications. or, more likely, for the limit value K = 1, which is associated with a discontinuity appearing in the pressure and velocity profile. Comparisons with interactive-boundary-layer and Navier-Stokes computations seem fairly supportive. The occurrence of the singularity offers an explanation for the appearance of a pronounced second minimum in numerous computed skin-friction plots, the numerical difficulties encountered in all reversed-flow computations, and the start of airfoil stall. The theory of the breakdown (which is modified for unsteady motions in an allied paper) also has widespread application, being relevant to all the interactive separating flows known to date, including internal and external two-dimensional or three-dimensional boundary layers and wakes.

Three-dimensional transverse instabilities in detached boundary layers

2007 ◽  
Vol 571 ◽  
pp. 221-233 ◽  
Author(s):  
FRANÇOIS GALLAIRE ◽  
MATTHIEU MARQUILLIE ◽  
UWE EHRENSTEIN
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Linear Analysis ◽  
Navier Stokes ◽  
Physical Origin ◽  
Viscous Effects ◽  
Global Mode ◽  
Navier Stokes Equations ◽  
Recirculation Bubble

A direct numerical simulation of the incompressible Navier–Stokes equations of the flow over a bump shows a stationary longitudinal instability at a Reynolds number of Re = 400. A three-dimensional global mode linear analysis is used to interpret these results and shows that the most unstable eigenmode is steady and localized in the recirculation bubble, with spanwise wavelength of approximately ten bump heights. An inviscid geometrical optics analysis along closed streamlines is then proposed and modified to account for viscous effects. This motivates a final discussion regarding the physical origin of the observed instability.

Unsteady Aerodynamic Characteristics of a High Speed Train with Crosswind

2011 ◽  
Vol 66-68 ◽  
pp. 1878-1882
Author(s):  
Ming Lu Zhang ◽  
Yi Ren Yang ◽  
Chen Guang Fan ◽  
Li Lu
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
High Speed ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Vehicle Speed ◽  
High Speed Train ◽  
Mesh Method

The aerodynamic performances of a high speed train will significant change under the action of the crosswind. Large eddy simulation (LES) was made to solve the flow around a simplified CRH2 high speed train with 250km/h and 350km/h under the influence of a crosswind with 28.4m/s base on the finite volume method and dynamic layering mesh method and three dimensional incompressible Navier-Stokes equations. Wind tunnel experimental method of static train with relative flowing air and dynamic mesh method of moving train were compared. The results of numerical simulation show that the flow field around train is completely different between Wind tunnel experiment and factual running. Many vortices will be produced on the leeside of the train with alternately vehicle bottom and back under the influence of a crosswind. The flow field around train is similar with different vehicle speed.

ON NONPARALLEL STABILITY OF THREE-DIMENSIONAL COMPRESSIBLE BOUNDARY LAYERS

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1503-1506
Author(s):  
JIXUE LIU ◽  
DENGBIN TANG ◽  
GUOXING ZHU
Keyword(s):  
Boundary Layers ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Local Method ◽  
Curvature Variation ◽  
Compressible Boundary Layers ◽  
Curvilinear Coordinate ◽  
The Difference

Nonparallel stability of the compressible boundary layers for three-dimensional configurations having large curvature variation on the surface is investigated by using the parabolic stability equations, which are derived from the Navier-Stokes equations in the curvilinear coordinate system. The difference schemes with fourth-order accuracy can be used in the entire computational regions. The global method is combined with the local method using a new iterative formula, thus more precise eigenvalues are obtained, and fast convergences are achieved. Computed curves of the amplification factor and shape functions of disturbances show clearly variable process of the flow stability, and agree well with other available results.

A Numerical Analysis of the Three-Dimensional Viscous Flow in a Transonic Compressor Rotor and Comparison With Experiment

1987 ◽  
Vol 109 (1) ◽  
pp. 83-90 ◽  
Author(s):  
W. N. Dawes
Keyword(s):  
Boundary Layer ◽  
Numerical Analysis ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Flow ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Transonic Compressor ◽  
Compressor Rotor

The numerical analysis of highly loaded transonic compressors continues to be of considerable interest. Although much progress has been made with inviscid analyses, viscous effects can be very significant, especially those associated with shock–boundary layer interactions. While inviscid analyses have been enhanced by the interactive inclusion of blade surf ace boundary layer calculations, it may be better in the long term to develop efficient algorithms to solve the full three-dimensional Navier–Stokes equations. Indeed, it seems that many phenomena of key interest, like tip clearance flows, may only be accessible to a Navier–Stokes solver. The present paper describes a computer program developed for solving the three-dimensional viscous compressible flow equations in turbomachine geometries. The code is applied to the study of the flowfield in an axial-flow transonic compressor rotor with an attempt to resolve the tip clearance flow. The predicted flow is compared with laser anemometry measurements and good agreement is found.

Effects of Streamwise Vortices on Laminar Boundary-Layer Flow

1968 ◽  
Vol 35 (2) ◽  
pp. 424-426 ◽  
Author(s):  
T. K. Fannelop
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Stokes Equations ◽  
Transverse Velocity ◽  
Three Dimensional ◽  
Perturbation Expansion ◽  
Navier Stokes ◽  
Boundary Layer Equations ◽  
Dimensional Boundary ◽  
Layer Flow

The effects of periodic transverse velocity fluctuations are investigated for boundary-layer flow over a flat plate. The method used is a perturbation expansion of the three-dimensional boundary-layer equations in terms of the small transverse velocity component. The equations are reduced to similarity form by means of suitable transformations. The second-order terms are expressed in terms of the first-order (Blasius) variables and are found to increase linearly with the streamwise coordinate. The present heat-transfer solution agrees with the more qualitative results of Persen. The derived velocity profiles are in exact agreement with the results of Crow’s more elaborate analysis based on the Navier-Stokes equations.

Study on the Mixing Performance Inside a Micromixer by Using Rapid-Prototyping Technology and Micro-LIF System

2004 ◽  
Author(s):  
Hyeung Seok Heo ◽  
Yong Kweon Suh
Keyword(s):  
Rapid Prototyping ◽  
Stokes Equations ◽  
Pure Water ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Commercial Code ◽  
Stirring Effect ◽  
Flow Motion

In this study a newly fabricated micromixer is proposed. This design comprises periodically arranged simple blocks. In this configuration, the stirring is greatly enhanced at a certain parameter set. This device is fabricated by rapid prototyping technology, stereolithography method, so that we can reduce the R&D time and cost. To characterize the flow field and the stirring effect both the numerical and experimental methods were employed. To obtain the material deformation, three-dimensional numerical computation to the Navier Stokes equations are performed by using a commercial code, FLUENT 6.0. Numerical results show that materials are deformed by the counter clockwise spiral motion of the secondary flows. In the experiment, flow visualization for the stirring effect is performed by using pure water in one reservoir and water mixed with a fluorescent dye in the other, so that we can see the flow motion inside the microchannel. The numerical and experiment results show that the stirring is significantly enhanced at larger block-height. We assert that we can apply the rapid-prototyping technology in the micro fabrication.

Analysis of Flow Separation in a Confined Two-Dimensional Channel

1970 ◽  
Vol 92 (4) ◽  
pp. 908-914 ◽  
Author(s):  
A. C. Hurd ◽  
A. R. Peters
Keyword(s):  
Wind Tunnel ◽  
Stokes Equations ◽  
Constant Width ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Measured Velocity ◽  
Laminar Separation ◽  
Low Speed Wind Tunnel

A two-dimensional incompressible isothermal laminar separation of a Newtonian fluid in steady flow was investigated. The geometry chosen for this study was a constant-width channel with a sharp 90-deg turn. It was found that an adaptation of a numerical solution for the Navier-Stokes equations first proposed by Allen gave convergence for all Reynolds numbers in the laminar range. The analytical results were compared with measured velocity profiles from a very low-speed wind tunnel.

The Calculation of Three-Dimensional Viscous Flow Through Multistage Turbomachines

1992 ◽  
Vol 114 (1) ◽  
pp. 18-26 ◽  
Author(s):  
J. D. Denton
Keyword(s):  
Stokes Equations ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Navier Stokes Equations ◽  
High Pressure Ratio ◽  
Machine Performance ◽  
Multistage Turbine ◽  
Flow Through

The extension of a well-established three-dimensional flow calculation method to calculate the flow through multiple turbomachinery blade rows is described in this paper. To avoid calculating the unsteady flow, which is inherent in any machine containing both rotating and stationary blade rows, a mixing process is modeled at a calculating station between adjacent blade rows. The effects of this mixing on the flow within the blade rows may be minimized by using extrapolated boundary conditions at the mixing plane. Inviscid calculations are not realistic for multistage machines and so the method includes a range of options for the inclusion of viscous effects. At the simplest level such effects may be included by prescribing the spanwise variation of polytropic efficiency for each blade row. At the most sophisticated level viscous effects and machine performance can be predicted by using a thin shear layer approximation to the Navier–Stokes equations and an eddy viscosity turbulence model. For high-pressure-ratio compressors there is a strong tendency for the calculation to surge during the transient part of the flow. This is overcome by the use of a new technique, which enables the calculation to be run to a prescribed mass flow. Use of the method is illustrated by applying it to a multistage turbine of simple geometry, a two-stage low-speed experimental turbine, and two multistage axial compressors.

Investigating Three-Dimensional and Rotational Effects on Wind Turbine Blades by Means of a Quasi-3D Navier-Stokes Solver

2000 ◽  
Vol 122 (2) ◽  
pp. 330-336 ◽  
Author(s):  
P. K. Chaviaropoulos ◽  
M. O. L. Hansen
Keyword(s):  
Wind Turbine ◽  
Stokes Equations ◽  
Twist Angle ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Wind Turbine Blades ◽  
Mean Values ◽  
Power Curves

Three-dimensional and rotational viscous effects on wind turbine blades are investigated by means of a quasi-3D Navier-Stokes model. The governing equations of the model are derived from the 3-D primitive variable Navier-Stokes equations written in cylindrical coordinates in the rotating frame of reference. The latter are integrated along the radial direction and certain assumptions are made for the mean values of the radial derivatives. The validity of these assumptions is cross-checked through fully 3-D Navier-Stokes calculations. The resulting quasi-3D model suggests that three-dimensional and rotational effects be strongly related to the local chord by radii ratio and the twist angle. The equations of the model are numerically integrated by means of a pressure correction algorithm. Both laminar and turbulent flow simulations are performed. The former is used for identifying the physical mechanism associated with the 3-D and rotational effects, while the latter for establishing semiempirical correction laws for the load coefficients, based on 2-D airfoil data. Comparing calculated and measured power curves of a stall controlled wind turbine, it is shown that the suggested correction laws may improve significantly the accuracy of the predictions. [S0098-2202(00)02702-4]

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