PIV and POD Investigations of Coherent Vortices Downstream Circular or Rectangular Obstacles Located Between Two Parallel Plates

2019 ◽  
Author(s):  
Fethi Aloui ◽  
Amal Elawady ◽  
Khaled J. Hammad
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Chaotic Behavior ◽  
Rectangular Channel ◽  
Experimental Investigations ◽  
Parallel Plates ◽  
Piv Measurements ◽  
Coherent Vortices ◽  
Karman Vortex ◽  
Proper Orthogonal

Abstract The study is an experimental investigations using PIV. The measurements were obtained by PIV for an unsteady laminar flow across a rectangular channel with a cross-section 300 × 30mm2, in the middle of which is located a cylindrical or a square obstacle. In the case of the cylindrical configuration and due to the confinement, PIV measurements in the range of 40 < Re < 200 clearly show that the von Karman vortex shedding appears at a critical Reynolds number which is about 66. A post-processing of these PIV measurements using the Proper Orthogonal Decomposition (POD) technique is by keeping only the first most energetic six modes, can be used as a filtering process to remove noise from instantaneous velocity signals. In the case of the square obstacle, PIV measurements obtained in the range of 30 < Re < 350 show the absence of vortex detachments and the chaotic behavior of the wake behind the obstacle beyond a certain Reynolds number. By examining the POD post-possessing results, the existence of a dynamic detachments’ regime (instantaneous breaking and coalescence of vortices), can be clearly observed. Given the chaotic behavior of the wake behind the obstacle, the application of the POD filtering process to only the first most energetic modes, cannot lead to good results.

Difference in Critical Reynolds Number Between Hagen-Poiseuille and Plane Poiseuille Flows

2001 ◽  
Author(s):  
Hidesada Kanda
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Poiseuille Flow ◽  
Average Velocity ◽  
Critical Reynolds Number ◽  
Inlet Section ◽  
Parallel Plates ◽  
Plane Poiseuille Flow ◽  
Contraction Ratio ◽  
Significant Difference

Abstract For plane Poiseuille flow, results of previous investigations were studied, focusing on experimental data on the critical Reynolds number, the entrance length, and the transition length. Consequently, concerning the natural transition, it was confirmed from the experimental data that (i) the transition occurs in the entrance region, (ii) the critical Reynolds number increases as the contraction ratio in the inlet section increases, and (iii) the minimum critical Reynolds number is obtained when the contraction ratio is the smallest or one, and there is no-shaped entrance or straight parallel plates. Its value exists in the neighborhood of 1300, based on the channel height and the average velocity. Although, for Hagen-Poiseuille flow, the minimum critical Reynolds number is approximately 2000, based on the pipe diameter and the average velocity, there seems to be no significant difference in the transition from laminar to turbulent flow between Hagen-Poiseuille flow and plane Poiseuille flow.

Computerized Model of Transition in Circular Pipe Flows: Part 1 — Experimental Definition of the Problem

1999 ◽  
Author(s):  
Hidesada Kanda
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Critical Reynolds Number ◽  
Natural Disturbance ◽  
Reynolds Numbers ◽  
Entrance Region ◽  
Circular Pipe ◽  
Experimental Investigations ◽  
Circular Pipes ◽  
Definition Of

Abstract A conceptual model was constructed for the problem of determining in circular pipes the conditions under which the transition from laminar to turbulent flow occurs, so that it becomes possible to calculate the minimum critical Reynolds number. Up until now this problem has been investigated by stability theory with disturbances at the pipe inlet. However, the minimum critical Reynolds number has not yet been obtained theoretically. Hence, the author took up the problem directly from many previous experimental investigations and found that (i) plots of the transition length versus the Reynolds number show that the transition occurs in the entrance region under the condition of a natural disturbance, and (ii) plots of the critical Reynolds number versus the ratio of bellmouth diameter to the pipe diamter show that with larger shapes of bellmouths, laminar flow will persist to higher Reynolds numbers. The problem is thus defined clearly as: Under the condition of an ordinary disturbance, the transition from laminar to turbulent flow occurs in the entrance region of a straight circular pipe, then the Reynolds number takes a minimum value of about 2000.

scholarly journals Finite Element Simulation of Newtonian and Non-Newtonian Fluid through the Parallel Plates Affixed with Single Screen

2020 ◽  
Vol 13 (1) ◽  
pp. 69-83
Author(s):  
Abid Ali Memon ◽  
Muhammad Asif Memon ◽  
Kaleemullah Bhatti ◽  
Gul Muhammad Shaikh
Keyword(s):  
Reynolds Number ◽  
Finite Element ◽  
Newtonian Fluid ◽  
Flow Rate ◽  
Rectangular Channel ◽  
Maximum Flow ◽  
Least Square ◽  
Maximum Flow Rate ◽  
Parallel Plates ◽  
The Impact

In the contemporary research article we have performed a numerical investigation of the non-Newtonian fluid flow through a rectangular channel with a fixed solid screen devoted at the angles 100 to 450 degrees. We have employed the power-law model for shear thickening and shear thinning fluids with the high Reynolds number between 1000 and 10,000. The obstacle has been solved by putting in the Galerkin’s least square strategy of the finite element method and the procedure has been carried out utilizing the commercial software COMSOL Multiphysics. Various flow properties such as 'maximum flow rate' and 'pressure' have been discussed in the terms of the Reynolds number and also using the linear and quadratic regressions in order to establish the relationship between them for the future analysis. Moreover the impact of turning screen in the shape of increment in the maximum flow rate and pressure is checked in terms of Reynolds number and  Satisfactory results are gained in comparison with the results available in the literature.

A Theory of Transitional and Turbulent Flow of Non-Newtonian Slurries Between Flat Parallel Plates

1971 ◽  
Vol 11 (01) ◽  
pp. 52-56 ◽  
Author(s):  
Richard W. Hanks ◽  
Maheshkumar P. Valia
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Critical Reynolds Number ◽  
Frictional Resistance ◽  
Newtonian Fluids ◽  
Transitional Flow ◽  
Parallel Plates ◽  
Bingham Plastic ◽  
Turbulent Transition ◽  
Large Width

Abstract A theoretical model is developed which Permits prediction of velocity profiles and frictional prediction of velocity profiles and frictional resistance factors for the isothermal flow of Bingham plastic non-Newtonian slurries in laminar, transitional, and turbulent flow between that parallel walls, in rectangular ducts of large width-to-height ratios, or in concentric annuli with radius ratios approaching unity. The theory is tested with available frictional resistance data for a range of Hedstrom numbers from 10(4) to 10(8) and a set of theoretical design curves of friction factor vs Reynolds number is developed. The model indices that for certain ranges of Hedstrom number (the non-Newtonian index) turbulence is suppressed relative to Newtonian flow behavior, whereas for other ranges of Hedstrom number, the converse is true. Introduction The handling of non-Newtonian fluids in turbulent motion is an important operation in many modern technological processes. Despite this fact, however, little has been done to develop models which are comparable to those available for Newtonian turbulent flow. In particular, a model of the transitional flow regime is notably lacking. Recently, a theory of laminar-turbulent transition for non-Newtonian slurries flowing in pipes and parallel plates was presented. A theory of parallel plates was presented. A theory of transitional and turbulent flow of Newtonian fluids in pipes and parallel plate ducts has also recently been developed. This theory permits the analytic calculation of the friction factor-Reynolds number curves as a continuous function of Reynolds number from the critical Reynolds number of laminar turbulent transition to any condition of turbulent flow. In this paper these two theories will be combined in order to develop a theory for the transitional and turbulent flow of non-Newtonian slurries in parallel plate ducts, rectangular ducts of large width-to-height ratio, or concentric annuli with radius ratios approaching unity. THEORETICAL ANALYSIS The rheological model which will be used to represent the non-Newtonian slurry behavior is the linear Bingham plastic model, ..............(1) ............(2) For this model the laminar flow curve is given by ..............(3) where q = 2v/b, b is one-half the distance between the plates, w = b(−dp/dz) is the wall shear stress, and D = o/ w. The end of the laminax flow, region is determined by the equations ........(4) .........(5) where N Rec = 4bp vc/ p is the critical Reynolds number, Dc is the critical transitional value of D and N He -16bp o/ p is the Hedstrom number expressed in terms of the hydraulic diameter for parallel plates. parallel plates. The calculation of the transitional flow field for this type of fluid will be based upon the model developed by Hanks for Newtonian fluids. SPEJ P. 52

scholarly journals Numerical Computations of Vortex Formation Length in Flow Past an Elliptical Cylinder

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 157
Author(s):  
Matthew Karlson ◽  
Bogdan G. Nita ◽  
Ashwin Vaidya
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Vortex Formation ◽  
Project Based Learning ◽  
Unsteady Regime ◽  
Karman Vortex ◽  
Elliptical Cylinders ◽  
Asymmetric Configuration

We examine two dimensional properties of vortex shedding past elliptical cylinders through numerical simulations. Specifically, we investigate the vortex formation length in the Reynolds number regime 10 to 100 for elliptical bodies of aspect ratio in the range 0.4 to 1.4. Our computations reveal that in the steady flow regime, the change in the vortex length follows a linear profile with respect to the Reynolds number, while in the unsteady regime, the time averaged vortex length decreases in an exponential manner with increasing Reynolds number. The transition in profile is used to identify the critical Reynolds number which marks the bifurcation of the Karman vortex from steady symmetric to the unsteady, asymmetric configuration. Additionally, relationships between the vortex length and aspect ratio are also explored. The work presented here is an example of a module that can be used in a project based learning course on computational fluid dynamics.

Experimental Determination of Transition to Turbulence in a Rectangular Channel With Eddy Promoters

1994 ◽  
Vol 116 (3) ◽  
pp. 484-487 ◽  
Author(s):  
J. S. Kapat ◽  
J. Ratnathicam ◽  
B. B. Mikic´
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Rectangular Channel ◽  
Transition To Turbulence ◽  
Channel Height ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Power Spectral ◽  
Unstable Configuration

We report on laminar-to-turbulent transition in a rectangular channel in the presence of periodically placed cylindrical eddy promoters. Transition is identified through the analysis of power spectral density (PSD) of velocity fluctuations. Placement of the eddy promoters in the channel, depending on the geometric configuration, can significantly reduce the value of Reynolds number at transition. The critical Reynolds number (based on the average velocity and the channel height) ranges from 1500 (for an unobstructed channel) to about 400 (for the most unstable configuration we have deployed). For all the configurations tested, demarcation of transition can be correlated with the expression: Reτ≡τ¯w,αv/ρH/2/ν=44˜51, where τw,αv is the spatially averaged value of mean wall shear stress and H is the channel height.

scholarly journals Finite Element Simulation of Newtonian and Non-Newtonian Fluid through the Parallel Plates Affixed with Single Screen

2020 ◽  
Vol 13 (1) ◽  
pp. 69-83
Author(s):  
Abid Ali Memon ◽  
Muhammad Asif Memon ◽  
Kaleemullah Bhatti ◽  
Gul Muhammad Shaikh
Keyword(s):  
Reynolds Number ◽  
Finite Element ◽  
Newtonian Fluid ◽  
Flow Rate ◽  
Rectangular Channel ◽  
Maximum Flow ◽  
Least Square ◽  
Maximum Flow Rate ◽  
Parallel Plates ◽  
The Impact

In the contemporary research article we have performed a numerical investigation of the non-Newtonian fluid flow through a rectangular channel with a fixed solid screen devoted at the angles 100 to 450 degrees. We have employed the power-law model for shear thickening and shear thinning fluids with the high Reynolds number between 1000 and 10,000. The obstacle has been solved by putting in the Galerkin’s least square strategy of the finite element method and the procedure has been carried out utilizing the commercial software COMSOL Multiphysics. Various flow properties such as 'maximum flow rate' and 'pressure' have been discussed in the terms of the Reynolds number and also using the linear and quadratic regressions in order to establish the relationship between them for the future analysis. Moreover the impact of turning screen in the shape of increment in the maximum flow rate and pressure is checked in terms of Reynolds number and  Satisfactory results are gained in comparison with the results available in the literature.

An Experimental Investigation of Transition of a Plane Poiseuille Flow

1974 ◽  
Vol 96 (4) ◽  
pp. 384-388 ◽  
Author(s):  
M. A. Karnitz ◽  
M. C. Potter ◽  
M. C. Smith
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Transition Process ◽  
Channel Height ◽  
Experimental Facility ◽  
Parallel Plates ◽  
Plane Poiseuille Flow ◽  
Theoretical Limit ◽  
Tollmien Schlichting ◽  
The Waves

The transition process of laminar flow between parallel plates is investigated experimentally. This problem has recently gained much attention with several reported works; however, the maximum transition Reynolds number reported has been approximately 3000 (based on average velocity and channel height) whereas the theoretical critical Reynolds number is 7700. Primary emphasis in this work is on approaching the theoretical limit in an experimental facility. A high aspect ratio (70 to 1) channel was used with air as the fluid. As the disturbance level at the entrance to the parallel plate section was reduced the transition Reynolds number increased monotonically. At a disturbance level of 0.3 percent the transition Reynolds number was 6700. Near transition small nearly sinusoidal waves in the critical shear layer were observed. The frequency of the waves was approximately 70 hertz, close to the frequency associated with the Tollmien-Schlichting waves of the critical point of linear theory. Sinusoidal waves preceded a turbulent burst which possessed an essentially plane front as it traveled downstream. As the Reynolds number was increased the bursting rate increased and the flow eventually became completely turbulent.

scholarly journals Finite Element Analysis of Fluid Flow through the Screen Embedded between Parallel Plates with High Reynolds Numbers

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Abid A. Memon ◽  
Hammad Alotaibi ◽  
M. Asif Memon ◽  
Kaleemullah Bhatti ◽  
Gul M. Shaikh ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Stokes Equations ◽  
Rectangular Channel ◽  
General Pattern ◽  
Resistance Coefficient ◽  
Least Square ◽  
Final Conclusion ◽  
Linear Regression Method ◽  
Parallel Plates

This paper provides numerical estimation of Newtonian fluid flow past through rectangular channel fixed with screen movable from 10° to 45° by increasing the Reynolds number from 1000 to 10,000. The two-dimensional incompressible Navier Stokes equations are worked out making use of the popular software COMSOL MultiPhysics version 5.4 which implements the Galerkin’s least square scheme to discretize the governing set of equations into algebraic form. In addition, the screen boundary condition with resistance coefficient (2.2) along with resistance coefficient 0.78 is implemented along with slip boundary conditions applied on the wall. We engaged to find and observe the relationship between the optimum velocity, drag force applied by the screen, and pressure occurred in the channel with increasing Reynolds number. Because of the linear relationship between the optimum velocities and the Reynolds number, applying the linear regression method, we will estimate the linear equation so that future prediction and judgment can be done. The validity of results is doing with the asymptomatic solution for stream-wise velocity at the outlet of the channel with screens available in the literature. A nondimensional quantity, i.e., ratio from local to global Reynolds number Re x / Re , is introduced which found stable and varies from -0.5 to 0.5 for the whole problem. Thus, we are in the position to express the general pattern of the velocity of the particles as well as the pressure on the line passing through the middle of the channel and depart some final conclusion at the end.

Hysteresis of Flow Around an Elliptic Cylinder in Critical Reynolds Number Regime

2005 ◽  
Author(s):  
Terukazu Ota ◽  
Seijiro Takahashi ◽  
Hiroyuki Yoshikawa
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Flow Characteristics ◽  
Elliptic Cylinder ◽  
Experimental Investigations ◽  
Hysteresis Phenomenon ◽  
Flow State ◽  
Axis Ratio ◽  
Fluid Forces ◽  
Wide Range

Experimental investigations of the flow around an elliptic cylinder of axis ratio 1:3 were carried out for several angles of attack in a wide range of Reynolds number. The flow characteristics were studied by measuring the fluid forces and the surface pressure. In the critical Reynolds number regime, a discontinuous change of flow state was observed. This change was accompanied by the remarkable hysteresis phenomenon. Details of this hysteresis process are described in the paper.

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