LES Study of the Influence of a Train-Nose Shape on the Flow Structures Under Cross-Wind Conditions

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Hassan Hemida ◽  
Siniša Krajnović
Keyword(s):  
High Speed ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Surface Flow ◽  
Flow Structures ◽  
Local Pressure ◽  
Freestream Velocity ◽  
Train Simulation ◽  
Long Nose

Cross-wind flows around two simplified high-speed trains with different nose shapes are studied using large-eddy simulation (LES) with the standard Smagorinsky model. The Reynolds number is 3×105 based on the height of the train and the freestream velocity. The cross section and the length of the two train models are identical while one model has a nose length twice that of the other. The three-dimensional effects of the nose on the flow structures in the wake and on the aerodynamic quantities such as lift and side force coefficients, flow patterns, local pressure coefficient, and wake frequencies are investigated. The short-nose train simulation shows highly unsteady and three-dimensional flow around the nose yielding more vortex structures in the wake. These structures result in a surface flow that differs from that in the long-nose train flow. They also influence the dominating frequencies that arise due to the shear-layer instabilities. Prediction of vortex shedding, flow patterns in the train surface, and time-averaged pressure distribution obtained from the long-nose train simulation are in good agreement with the available experimental data.

Investigations on Energy Shares and Flow Structures of the Mixing Flow Using 3D-POD Analyses

2019 ◽  
Author(s):  
Daekyeong Kong ◽  
Gyeongrae Cho ◽  
Myoung-Jin Kim ◽  
Deog Hee Doh ◽  
Sangmo Kang ◽  
...  
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Flow Structures ◽  
Optical Encoder ◽  
Energy Distributions ◽  
Three Dimensional Flow ◽  
Mixing Properties ◽  
Vortical Structures ◽  
Flow Features ◽  
Proper Orthogonal

Abstract The objective of this report is investigate the influences of the mixing state to the productions of the vaterite crystal of CaCO3. In order to quantify the three-dimensional flow structures and their physical contribution to the mixing properties, a stereoscopic PIV (SPIV) has been adopted. The SPIV systems consists of two high speed cameras and an optical encoder which is used for trigging the SPIV system to capture the instantaneous flow images. A continuous laser (550nm) has been used. For mixing, an agitator having four blades has been used. The mixing tank has been filled with water up to 85% level of the tank height. The agitator has been rotated with 200rpm, 250rpm and 300rpm, and the 3D flow structures have been captured by the constructed SPIV system. Using measured instantaneous 3D vectors, POD (proper orthogonal decomposition) analyses has been adopted to investigate the energy distributions of the major vortical structures, and to evaluate the flow features regarding on the production of the vaterite crystal of CaCO3.

Measurement of Viscoelastic Fluid Flow in the Curved Microchannel Using Digital Holographic Microscope and Polarized Camera

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Xiao-Bin Li ◽  
Masamichi Oishi ◽  
Tsukasa Matsuo ◽  
Marie Oshima ◽  
Feng-Chen Li
Keyword(s):  
Real Time ◽  
Viscoelastic Fluid ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Three Dimensional ◽  
Flow Structures ◽  
Tracer Particles ◽  
Microfluidic Flow ◽  
First Time ◽  
Measurement Approach

This paper aims to develop a three-dimensional (3D) measurement approach to investigate the flow structures of viscoelastic fluid in the curved microchannel by using digital holographic microscope (DHM). The measurement system uses off-axis holographic/interferometric optical setup for the moving target, and the real-time three-dimensional-three-components (3D3C) particle tracking velocimetry (PTV) can be achieved based on the analysis of phase information of holograms. To diagnose the irregular flow inside the microchannel, the 3D temporal positions of tracer particles in the volume of 282 μm × 282 μm × 60 μm have been detected and velocity field was calculated based on the PTV algorithm. Moreover, to explain the flow field inside the curved microchannel, for the first time the polarized high-speed camera was utilized to identify the strong elongation in the viscoelastic fluid. The DHM is proven to be successful for the measurements of microfluidic flow, especially for the truly real-time 3D motions.

Aerodynamic Simulation of the Air Flow beneath the High Speed Train

2012 ◽  
Vol 253-255 ◽  
pp. 2035-2040
Author(s):  
Ye Bo Liu ◽  
Zhi Ming Liu
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Air Flow ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Navier Stokes ◽  
High Speed Train ◽  
Navier Stokes Equations ◽  
Pressure Distributions ◽  
High Speed Trains

Numerical simulations were carried out to investigate the air flow and pressure distributions beneath high speed trains, based on the three-dimensional Reynolds-averaged Navier-Stokes equations with the SST k-ω two-equation turbulence model. The simulation scenarios were of the high speed train, the CRH2, running in the open air at four different speeds: 200km/h, 250km/h, 300km/h and 350km/h. The results show that, the highest area of pressure is located at the front underbody part of the train whist the pressure for rest of the train is relatively small. Increasing speed does not visibly increase the pressure coefficient, indicating that the pressure increases with the square of the operational speed.

3-D Flow Structures Around and Fluid-Dynamic Forces Acting on a Rectangular Cylinder in Oscillatory Flow

2003 ◽  
Author(s):  
Takahiro Yasuda ◽  
Atsushi Okajima ◽  
Minoru Moriyoshi
Keyword(s):  
Oscillatory Flow ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Flow Structures ◽  
Inertia Force ◽  
Water Tank ◽  
Height Ratio ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Rectangular Cylinder

Three-dimensional flow structures around and fluiddynamic forces acting on a rectangular cylinder in oscillatory flow were investigated by numerical simulation using finite volume method. The computations were carried out for three kinds of cross-sections with width/height ratio (d/H) d/H = 0.6, 1.0 and 2.0 and for the amplitude of oscillating flow in the range of 2.5 ≤ the Keulegan-Carpenter number (KC) ≤ 25, the Stokes number (β) = 95. The calculated flow patterns and the drag and inertia force coefficients of Morison equation acting on the cylinder were compared with the experimental ones using a U-tube water tank. In this paper, we note how the KC number and the width/height ratio of the cylinders affect the unsteady and three-dimensional flow structures such as the “longitudinal vortices” and “transverse street” which formed in the case of a circular cylinder fixed in oscillatory flow, and how the CD and the CM values of Morison coefficients change corresponding to the change of the behavior of the flow patterns. Furthermore the relationship between spanwise correlation coefficient of the transverse force R(x3), where x3 is the spanwise position from the bottom of the cylinder, and three-dimensional vortex structures were investigated.

scholarly journals The Design and Testing of a Radial Flow Turbine for Aerodynamic Research

1991 ◽  
Author(s):  
I. Huntsman ◽  
H. P. Hodson ◽  
S. H. Hill
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Three Dimensional ◽  
Surface Flow ◽  
Stream Line ◽  
Flow Visualisation ◽  
Gas Generator ◽  
Low Speed ◽  
Scaling Parameters ◽  
Design And Testing

This paper describes the design of a high-speed radial inflow turbine for use as part of a gas-generator, and the design of a large-scale (1.2 m tip dia.) low-speed model of the high-speed turbine. Stream-line curvature throughflow, two-dimensional blade-to-blade and fully three-dimensional inviscid and viscous calculation methods have been used extensively in the analysis of the designs. The use of appropriate scaling parameters and their impact on turbine performance is discussed. A simple model shows, for example, how to model the blade lean in the inducer which serves to balance the effect of meridional curvature at inlet to the rotor and can be used to unload the rotor tip. A brief description of the low speed experimental facility is followed by a presentation and discussion of experimental results. These include surface flow visualisation patterns on both the rotor and stator blades and blade row exit traverses.

Effects of Flow Patterns on Aerodynamic Forces of a Square Cylinder at Incidence

2011 ◽  
Vol 27 (3) ◽  
pp. 347-355 ◽  
Author(s):  
R. F. Huang ◽  
B. H. Lin
Keyword(s):  
Lateral Surface ◽  
Incidence Angle ◽  
Pressure Coefficient ◽  
Flow Patterns ◽  
Surface Flow ◽  
Square Cylinder ◽  
Pressure Distributions ◽  
New Findings ◽  
Drag And Lift ◽  
Critical Incidence

ABSTRACTThe pressure distributions around a square cylinder in a crossflow were experimentally studied in a wind tunnel. The subject of study was conventional, but the results presented new findings. The experiments were performed by using a home-made linear pressure scanner. The ranges of Reynolds number and incidence angle were 2 × 104- 9.4 × 104and 0° - 45°, respectively. According to the topological flow patterns, the flows around the square cylinder at incidence showed three characteristic regimes: The subcritical, supercritical, and wedge flows. A critical incidence angle αcri= 15° separated the regimes of subcritical and supercritical modes. The results of current study provided information regarding the effects of the topological flow patterns on surface pressure distribution, drag, and lift characteristics. The pressure distributions, drag, and lift presented different characteristics in different characteristic flow regimes and had close correlations with the flows. At the critical incidence angle 15° which separated the subcritical and supercritical regimes, the surface-averaged pressure coefficient on each face displayed local extreme value—The drag coefficient attained a minimum of 1.6, the lateral force coefficient reached a maximum of 0.9. The appearance of the minimum drag at the critical incidence angle was attributed to the reduction of wake width which was induced by two surface flow phenomena: (1) reattachment of the separated boundary layer on the lateral surface facing windward at the critical incidence angle and (2) flow pattern change on the lateral surface facing leeward.

Visualization of Three-Dimensional Flow Structures Caused by Rotating Instability

2019 ◽  
Author(s):  
Julija Peter ◽  
Paul Uwe Thamsen
Keyword(s):  
High Speed ◽  
Spectral Characteristics ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Flow Structures ◽  
Experimental Investigations ◽  
Flow Topology ◽  
Time Resolved ◽  
Characteristic Flow ◽  
Rotating Instability

Abstract The present study deals with the flow phenomenon Rotating Instability (RI), which is predominantly observed in axial compressors at off-design conditions e.g. near stall. It potentially induces noise and triggers blade vibrations. Despite numerous studies, the characteristics and the source of RI are not completely understood. The objective of this work is to identify and to visualize characteristic flow topology corresponding to RI by means of Stereo High Speed Particle Image Velocimetry (PIV). The experimental investigations were carried out in an annular compressor stator cascade with and without hub clearance at an inflow Mach number of Ma = 0.4 and the Reynolds number of Re = 300 000. The time-resolved 3C flow field is measured in a single blade passage in planes tangential to the hub. Additionally, the time-resolved pressure fluctuations are captured synchronously to the PIV system. By using combined correlation techniques the spectral characteristics, the spatial extension of the RI and the characteristic flow structures were identified and visualized in configurations with and without hub clearance. The investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without hub clearance. Overall, this work gives important insights into the complex phenomenon Rotating Instability, which can be taken into account when developing compressors in the future.

Effects of Elastic Modulus Change in Helical Tubes Under the Influence of Dynamic Changes in Curvature and Torsion

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
N. K. C. Selvarasu ◽  
Danesh K. Tafti
Keyword(s):  
Elastic Modulus ◽  
Secondary Flow ◽  
Dynamic Change ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Local Pressure ◽  
Moving Wall ◽  
Vorticity Flux ◽  
Late Restenosis ◽  
Curvature And Torsion

The incidence of stent late restenosis is high (Zwart et al., 2010, “Coronary Stent Thrombosis in the Current Era: Challenges and Opportunities for Treatment,” Curr. Treat. Options Cardiovasc. Med., 12(1), pp. 46–57) despite the extensive use of stents, and is most prevalent at the proximal and distal ends of the stent. Elastic modulus change in stented coronary arteries subject to the motion of the myocardium is not studied extensively. It is our objective to understand and reveal the mechanism by which changes in elastic modulus and geometry contribute to the generation of nonphysiological wall shear stress (WSS). Such adverse hemodynamic conditions could have an effect on the onset of restenosis. Three-dimensional (3D), spatiotemporally resolved computational fluid dynamics (CFD) simulations of pulsatile flow with moving wall boundaries and fluid structure interaction (FSI) were carried out for a helical artery with physiologically relevant flow parameters. To study the effect of coronary artery (CA) geometry change on stent elastic modulus mismatch, models where the curvature, torsion and both curvature and torsion change were examined. The elastic modulus is increased by a factor of two, five, and ten in the stented section for all three modes of motion. The changes in elastic modulus and arterial geometry cause critical variations in the local pressure and velocity gradients and secondary flow patterns. The pressure gradient change is  47%, with respect to the unstented baseline when the elastic modulus is increased to 10. The corresponding WSS change is 15.4%. We demonstrate that these changes are attributed to the production of vorticity (vorticity flux) caused by the wall movement and elastic modulus discontinuity. The changes in curvature dominate torsion changes in terms of the effects to local hemodynamics. The elastic modulus discontinuities along with the dynamic change in geometry affected the secondary flow patterns and vorticity flux, which in turn affects the WSS.

Prediction of Developing Turbulent Flow in a 90° Curved Duct Using Linear and Nonlinear Low-Re k-ε Models

Volume 1 ◽  
2004 ◽  
Author(s):  
M. Raisee ◽  
H. Alemi ◽  
H. Iacovides
Keyword(s):  
Turbulent Flow ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Main Stream ◽  
Local Pressure ◽  
Flow Measurements ◽  
Numerical Predictions ◽  
Flow Development ◽  
Curved Section

This paper reports the outcome of applying two different low-Re number eddy-viscosity models to resolve the complex three-dimensional motion that arises in turbulent flow in a square cross-section duct passing around a 90° bend. Flow computations have been obtained using a three-dimensional, non-orthogonal flow solver. For modeling of turbulence, the Launder and Sharma low-Re k–ε model and a recently modified version of nonlinear low-Re k–ε model that have been shown to be suitable for flow and thermal predictions in re-circulating and impinging jet flows, have been employed. A bounded version of the QUICK scheme was used for the approximation of convection in all transport equations. The numerical predictions are validated through comparisons with the reported flow measurements and are used to explain how the curvature influences the flow development. The results of the present investigation indicate that the curvature induces a strong secondary flow in the curved section of the duct. The secondary motion also persists downstream of the bend, although it slowly disappears with the main stream development. At the entrance of the curved section, the curvature alters the flow development by displacing the fluid towards the convex (inner) wall. Comparisons of the predicted stream-wise and cross-stream velocity components with the measured data indicate that both turbulence models employed in the present study can produce reasonable predictions, although the non-linear model predictions are generally closer to the measurements. Both turbulence models successfully reproduce the distribution as well as the levels of the local pressure coefficient in the curved section of the duct.

Three-dimensional separated flow structure over prolate spheroids

1990 ◽  
Vol 429 (1876) ◽  
pp. 73-90 ◽  
Keyword(s):  
Flow Pattern ◽  
Flow Structure ◽  
Three Dimensional ◽  
Separated Flow ◽  
Flow Patterns ◽  
Surface Flow ◽  
Water Tunnel ◽  
Entire Body ◽  
Prolate Spheroids ◽  
First Time

Colour poster paints were used for water-tunnel visualization of the surface flow patterns over prolate spheroids of axis-ratios b / a = ½, ⅓ and ¼ at incidence from 0-90°. Results display the surface flow pattern over the entire body presumably for the first time in terms of completeness and clarify unsettled questions in the literature.

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