Evolution of Vortices Behind Single Diamond-Shaped Cylinders in Free Stream

2000 ◽  
Author(s):  
Shuichi Torii ◽  
Wen-Jei Yang ◽  
Shinzaburo Umeda
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Free Stream ◽  
Finite Difference Methods ◽  
Time History ◽  
Experimental Program ◽  
Flow Phenomena ◽  
Vector Distribution ◽  
Two Dimensional Flow ◽  
Karman Vortex

Abstract Two-dimensional flow over a single diamond-shaped cylinder in the free stream are experimentally and theoretically investigated. The experimental program includes visualization of the flow field using the tracer method. In the theoretical program, the Navier-Stoeks equations are discretized using finite difference methods to determine the time history of velocity vector distribution in the flow field. Efforts directed to examine the effects of the Reynolds number, Re, and the upstream angle of the diamond shape, θ, on flow phenomena. The study discloses that (i) the generation of von Karman vortex streets behind the diamond-shaped cylinder are intensified with an increase in the Reynolds number, (ii) the flow pattern in the wake region of the diamond-shaped island is affected by θ, and (iii) the relationship among the Strouhal number, St, Re and θ is determined and compared with the existing St-Re relationship for flow over a circular cylinder.

Successive stages and the role of natural vortex dislocations in three-dimensional wake transition

2001 ◽  
Vol 439 ◽  
pp. 1-41 ◽  
Author(s):  
M. BRAZA ◽  
D. FAGHANI ◽  
H. PERSILLON
Keyword(s):  
Reynolds Number ◽  
Stability Theory ◽  
Longitudinal Velocity ◽  
Three Dimensional ◽  
Time History ◽  
Optimum Shape ◽  
Cylinder Wake ◽  
Two Dimensional Flow ◽  
Karman Vortex ◽  
Definition Of

The time-history of the development of the three-dimensional transition features in a nominally two-dimensional flow configuration is established for Reynolds number 220 in a cylinder wake. The identification of the successive stages that evolve very fast during experiments is possible by means of direct numerical simulation. The physical processes related to the creation of streamwise and vertical vorticity components and their impact on the spanwise waviness of the main von Kármán vortex filaments are analysed by means of the Craik–Leibovich shearing instability mechanism and a comparative discussion is given with respect to the elliptic stability theory. This study proves the existence of a further stage in the three-dimensional transition, which substantially modifies the regular spanwise undulation. This is a systematic and repetitive development of natural vortex dislocations in the near wake. The definition of this kind of structure is provided, as well as its properties related to a drastic reduction of the fundamental frequency and to the selection of a lower path in the Strouhal–Reynolds number relation. The induced amplitude modulation of the flow properties along the span is also evaluated. Quantification of these properties is carried out by using wavelet analysis and autoregressive modelling of the time series. The reasons for the development of natural vortex dislocations are analysed and related to specific modulations of the spanwise structure of the longitudinal velocity upstream separation. From this part of the study an optimum shape for the spanwise distribution of this component can be specified, able to trigger the vortex dislocations in wake flows and therefore useful to apply in the context of stability theory analyses and in further DNS studies.

Unsteady Interaction of Labyrinth Seal Leakage Flow and Downstream Stator Flow in a Shrouded 1.5 Stage Axial Turbine

2005 ◽  
Author(s):  
P. Peters ◽  
J. R. Menter ◽  
H. Pfost ◽  
A. Giboni ◽  
K. Wolter
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Numerical Data ◽  
Labyrinth Seal ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Experimental Program ◽  
Leakage Flow ◽  
Axial Turbine ◽  
Flow Phenomena

This paper presents the results of experimental and numerical investigations into the flow in a 1.5-stage low-speed axial turbine with shrouded rotor blades and a straight through labyrinth seal. The paper focuses on the time dependent influence of the leakage flow on the downstream stator flow field. The experimental program consists of time accurate measurements of the three-dimensional properties of the flow through ten different measurement planes in the stator passage. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at the design operating point of the turbine. The measurement planes extend from the shroud to the casing. The complex three-dimensional flow field is mapped in great detail by 4,800 measurement points and 20 time steps per blade passing period. The time-accurate experimental data of the ten measurement planes was compared with the results of unsteady, numerical simulations of the turbine flow. The 3D-Navier-Stokes Solver CFX-TASCflow was used. The experimental and numerical results correspond well and allow detailed analysis of the flow phenomena. Additionally numerical data behind the rotor is used to connect the entry of the leakage flow with the flow phenomena in the downstream stator passage and behind it. The leakage flow causes strong fluctuations of the flow in the downstream stator. Above all, the high number of measurement points reveals both the secondary flow phenomena and the vortex structures within the blade passage. The time-dependence of both the position and the intensity of the vortices influenced by the leakage flow is shown. The paper shows that even at realistic clearance heights the leakage flow influences considerable parts of the downstream stator and gives rise to negative incidence and flow separation. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimization process of turbines.

Stability and Scalar Transport in Laminar Non-Newtonian Flow in a Bifurcating T-Junction

2019 ◽  
Author(s):  
Ajay Chatterjee ◽  
Fatemeh Khalkhal
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Numerical Solutions ◽  
Shear Thinning ◽  
Volume Averaging ◽  
Scalar Transport ◽  
Linear Perturbation ◽  
Perturbation Equation ◽  
Two Dimensional ◽  
Two Dimensional Flow

Abstract We consider the prototype bifurcating T-junction planar flow and compare the stability of the steady two-dimensional flow field for a Newtonian and a shear thinning inelastic fluid. Global stability of the flow to two-dimensional perturbations is analyzed using numerical solutions of the linear perturbation equation. Calculations are performed for two flow ratios between the main channel and the bifurcating channel, and for two different values of the time constant in the non-Newtonian rheological model. The results show that although the steady flow remains stable to two-dimensional perturbations for Newtonian Reynolds number up to ∼ 400, shear thinning is destabilizing in that the decay rate of the perturbation field is slower. The perturbation growth rate curves for all of the different cases may be correlated by volume averaging the local Reynolds number over the flow domain, indicating that the effect of shear thinning on stability may be described using a suitably defined average Reynolds number. These stability results provide some justification for CFD calculations of steady non-Newtonian two-dimensional flows presented in earlier papers. Since scalar transport is of interest in this flow field, we also present some numerical calculations for the Nusselt number profile along the bifurcating channel wall. The results show that for the shear thinning fluid the scalar transport rate is differentially larger by ∼ 75% across one of the bifurcating channel walls, a consequence of fluid rheology enhancing the effect of flow asymmetry in the entrance region of the bifurcation.

Velocity Measurements Around Film Cooling Holes With Deposition

2010 ◽  
Author(s):  
Kristian Haase ◽  
Jeffrey P. Bons
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flat Plate ◽  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Flow Structures ◽  
Particle Image Velocimetry Technique ◽  
Film Cooling Holes

The choice of synthetic fuels (synfuels) in order to achieve greater fuel flexibility may lead to unwanted solid depositions on the blades of turbomachines. The objective of this paper is to gain information of the flow field over a turbine blade with depositions around the film cooling holes. For the investigation the particle image velocimetry technique (PIV) is utilized. The experiments are conducted in a low speed wind tunnel at a Reynolds number of 300,000 based on the distance from the leading edge to the middle of the cooling holes and a Reynolds number of 9,200 based on the hole diameter. Three different simulation plates are tested in the tunnel—a flat plate for comparison, a plate with large depositions only upstream of the holes, and one with smaller depositions all around the holes. The two deposition configurations are scaled models of actual depositions formed at simulated engine flow conditions on a turbine test coupon. The experiments are conducted at four different coolant to free stream blowing ratios—0, 0.5, 1, and 2—and at a density ratio of 1.1. PIV images are taken in four planes from the side of the tunnel to record the main flow structures and in five planes from the end of the tunnel to record the secondary flow structures. The results show that the type of deposition has a large influence on the flow field. With the smaller depositions the penetration of the coolant jet into the free stream is significantly reduced but the dimension and strength of the kidney vortices is increased compared to the flat plate. With the large depositions, on the other hand, the penetration of the coolant jet is much higher due to the ramp effect and the dimension of the secondary vortices is also increased. It can also be seen that the coolant gathers and stays behind the large depositions and then flows off very slowly. Film effectiveness and surface heat flux data acquired with the same plates (and reported previously) allow the identification of flow features and their direct influence on the film cooling performance.

Taylor vortices between two concentric rotating spheres

1982 ◽  
Vol 119 ◽  
pp. 1-25 ◽  
Author(s):  
Fritz Bartels
Keyword(s):  
Reynolds Number ◽  
Finite Difference ◽  
Flow Field ◽  
Critical Reynolds Number ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Finite Difference Methods ◽  
Taylor Vortices ◽  
Concentric Spheres ◽  
Inner Sphere

The laminar viscous flow in the gap between two concentric spheres is investigated for a rotating inner sphere. The solution is obtained by solving the Navier-Stokes equations by means of finite-difference techniques, where the equations are restricted to axially symmetric flows. The flow field is hydrodynamically unstable above a critical Reynolds number. This investigation indicates that the critical Reynolds number beyond which Taylor vortices appear is slightly higher in a spherical gap than for the flow between concentric cylinders. The formation of Taylor vortices could be observed only for small gap widths s ≤ 0·17. The final state of the flow field depends on the initial conditions and the acceleration of the inner sphere. Steady and unsteady flow modes are predicted for various Reynolds numbers and gap widths. The results are in agreement with experiment if certain accuracy conditions of the finite-difference methods are satisfied. It is seen that the equatorial symmetry is of great importance for the development of the Taylor vortices in the gap.

Three-dimensional numerical modeling of flow upstream of a symmetric streamlined body mounted over a flat plate with tip gap

2022 ◽  
pp. 095440622110470
Author(s):  
Ovais U Khan ◽  
Ghulam Arshed ◽  
Mohammad Javed Khan
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Numerical Simulations ◽  
Flat Plate ◽  
Free Stream ◽  
Three Dimensional ◽  
System Structure ◽  
Research Activity ◽  
Vortex System ◽  
Streamlined Body

In this research activity numerical simulations are carried out to investigate the flow field upstream of a symmetric streamlined body mounted perpendicular to a flat plate with and without clearance gap between the tip of the streamlined body and the flat plate with laminar boundary layer. The developed numerical model successfully predicted the three-dimensional horseshoe vortex system upstream of the streamlined body with and without the tip gap. The resulting vortex system for the configuration with tip gap contains multiple vortices with characteristics similar to that of end-wall-flows of surface-mounted obstacles. The effects of varying tip gap clearance for various values of free stream Reynolds number are also investigated. It was found that the introduction of a gap between the streamlined body tip and flat surface caused shifting of the vortex structure system in the upstream direction. Moreover, it is observed that the free stream Reynolds number and the tip gap between the streamlined body and the flat plate substantially influences the unsteady character of the flow field and the vortex system structure. Results obtained from the numerical simulations are compared with experimental measurements of a blunt body configuration and have been found in good agreement.

Forces Caused by the Radial Out-Flow Between Parallel Disks

1984 ◽  
Vol 106 (3) ◽  
pp. 292-297 ◽  
Author(s):  
C. E. Wark ◽  
J. F. Foss
Keyword(s):  
Reynolds Number ◽  
Ad Hoc ◽  
Reynolds Numbers ◽  
Experimental Program ◽  
Number Range ◽  
Parallel Disks ◽  
Flow Phenomena ◽  
Significant Disagreement ◽  
Low Reynolds ◽  
The Impact

An experimental program, to determine the magnitude of the force on the impact disk for the radial out-flow between parallel disks, has been carried out for moderate Reynolds numbers. The present results are compared with a previously published, ad hoc, analytical formulation whose coefficients were established for low Reynolds numbers. Acceptable agreement exists for the low Reynolds number range of the present study; progressively significant disagreement is observed as the Reynolds number is increased. The present force data, when combined with previous observations and interpreted via appropriate theoretical considerations, reveal a complex blending of flow phenomena for the Reynolds number, diameter ratio, and plate separation values of the present study.

scholarly journals Topological fluid mechanics of the formation of the Kármán-vortex street

2016 ◽  
Vol 812 ◽  
pp. 199-221 ◽  
Author(s):  
Matthias Heil ◽  
Jordan Rosso ◽  
Andrew L. Hazel ◽  
Morten Brøns
Keyword(s):  
Reynolds Number ◽  
Vortex Street ◽  
Feature Points ◽  
Vorticity Field ◽  
Karman Vortex Street ◽  
Extremal Points ◽  
Two Dimensional Flow ◽  
Kármán Vortex Street ◽  
Karman Vortex ◽  
Time Periodic

We explore the two-dimensional flow around a circular cylinder with the aim of elucidating the changes in the topology of the vorticity field that lead to the formation of the Kármán vortex street. Specifically, we analyse the formation and disappearance of extremal points of vorticity, which we consider to be feature points for vortices. The basic vortex creation mechanism is shown to be a topological cusp bifurcation in the vorticity field, where a saddle and an extremum of the vorticity are created simultaneously. We demonstrate that vortices are first created approximately 100 diameters downstream of the cylinder, at a Reynolds number, $Re_{K}$, which is slightly larger than the critical Reynolds number, $Re_{crit}\approx 46$, at which the flow becomes time periodic. For $Re$ slightly above $Re_{K}$, the newly created vortices disappear again a short distance further downstream. As $Re$ is further increased, the points of creation and disappearance move rapidly upstream and downstream, respectively, and the Kármán vortex street persists over increasingly large streamwise distances.

Effects of Free-Stream Turbulence Intensity and Frequency on Heat Transfer to Turbine Blading

1981 ◽  
Vol 103 (1) ◽  
pp. 60-64 ◽  
Author(s):  
F. J. Bayley ◽  
W. J. Priddy
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Free Stream ◽  
Turbine Blades ◽  
Theoretical Work ◽  
Experimental Program ◽  
Blade Surface ◽  
Free Stream Turbulence ◽  
Mainstream Flow ◽  
Turbine Blading

This paper describes a continuing experimental program in which the frequency and amplitude of turbulence in the mainstream flow over a cascade of turbine blades are separately and controllably varied. The effects of these two characteristics of the flow are demonstrated showing the significant effect of each upon the rates of convection to most of the blade surface. A correlation following the predictions of the theoretical work of reference [2] is shown to have some promise, although some modification is required to allow for changes in mainstream Reynolds number not accounted for by the usual normalizing procedure.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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