Wind Tunnel Experiments on Cooling Tower Plumes: Part 1—In Uniform Crossflow

1989 ◽  
Vol 111 (4) ◽  
pp. 941-948 ◽  
Author(s):  
J. Andreopoulos
Keyword(s):  
Reynolds Number ◽  
Cooling Tower ◽  
Velocity Ratio ◽  
Reynolds Numbers ◽  
Wind Tunnel Experiments ◽  
Low Velocity ◽  
Turbulent Structures ◽  
High Turbulence ◽  
High Reynolds ◽  
Number Case

Measurements of velocity and temperature field and flow visualization results are reported for an ideal case of a cooling-tower plume in the presence of a uniform crossflow for various velocity ratios, densimetric Froude numbers, and Reynolds numbers. Coherent structures in the form of jetlike, wakelike, or mushroom-type vortices have been observed. The type of structure depends primarily on the velocity ratio. As the Reynolds number increases, turbulent structures appear, which have vorticity of the same sign as the partner vortices in the low Reynolds number case. The measurements showed that there is a strong interaction between the bending plume or jet and the wake of the cooling tower, which is basically responsible for the downwash effect. The latter is generally quite strong at low velocity ratios and high Reynolds numbers. High turbulence intensities are produced in the wake of the tower for a distance of 6 to 8 diameters. The plume is diluted faster as the velocity ratio increases and buoyancy decreases. In the wake region of the stack dilution increases with increased buoyancy.

A Numerical Investigation of Flow Around a Circular Cylinder Near a Flat Boundary

2012 ◽  
Author(s):  
Mário Caruso Neto ◽  
Juan B. V. Wanderley
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Conservative Scheme ◽  
Gap Ratio ◽  
Number Variation ◽  
High Reynolds ◽  
Number Case

Flow around a pipeline near the seabed still remains relatively unknown in spite of the efforts of many researchers to understand the complicated flow around bluff bodies. The present study contributes to this discussion numerically investigating two-dimensional fluid flow around a circular cylinder near a flat plate. The investigation contemplates Reynolds numbers of 100, 180 and 7000 and a gap ratio (G/D) of 3, 0.6, 0.3 and 0.125. The flow is simulated considering a finite difference and total variation diminishing (TVD) conservative scheme with a Chimera domain division method to solve RANS equations. The k-e turbulence model is used to simulate the turbulent flow in the high Reynolds number case. Results are obtained for force coefficients and flow visualization. The results show a significant variation of flow characteristics with gap ratio and Reynolds number variation.

Effect of Neutrally Buoyant Particles on Horizontal Turbulent Flow Through a Tee-Junction

2020 ◽  
Author(s):  
Andrew M. Bluestein ◽  
Douglas Bohl
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Complex Flows ◽  
Turbulence Modulation ◽  
Flow Through ◽  
Tee Junction ◽  
High Reynolds ◽  
Neutrally Buoyant ◽  
Number Case

Abstract Turbulent particle-laden flows are of high interest due to their presence in many industrial applications. High Reynolds number flows containing solid particles, create complex flows and erosive environments. The effect that the particles have on the turbulence of the surrounding fluid is referred to in the literature as turbulence modulation. This is an area of research in which there is still much to learn to enable a deeper understanding of the physics behind these complex flows. Data that would be of particular usefulness are at higher Reynolds numbers (Re ≥ 100,000), and dense loadings (ΦV ≥ 1%). In this work, turbulent particle-laden flow through a simplified industrial geometry was studied at an upper Reynolds number of 115,000 and particle loadings up to 5% by weight/volume (specific gravity = 1) to address these needs. The flow within a tee junction with the 90-degree branch closed-off downstream was studied. This is analogous to a duct flow but with an exposed region of fluid at the location of the closed-off branch. Super absorbent particles were used as the solid phase, which became index-matched and neutrally buoyant upon saturation with water. Data were acquired using 2-D planar particle image velocimetry (PIV) along the center span of the tunnel. Mean and root-mean-square (rms) velocities were calculated for the fluid phase. Particle loadings studied were 0%, 1%, 3%, and 5 at flow Reynolds numbers of 11,500 and 115,000. Velocity contour plots are presented to provide a macro description of the flow. Three horizontal positions within the shear layer region were selected for profile comparison (x* = −0.45, 0, 0.45). Prior literature suggested that the particles would attenuate the turbulence, however, the result showed no single trend in the current data. The mean velocities were nominally unaffected by loading for a respective Reynolds number case. Turbulence modulation of the flow was found to be sensitive to the Reynolds number, as at x* = −0.45 weakening of the rms was observed in the low Reynolds number case and strengthening in the high Reynolds number case for the same particle loading in the same region of the geometry.

scholarly journals Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Nils Paul van Hinsberg
Keyword(s):  
Reynolds Number ◽  
Cross Sections ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Surface Boundary ◽  
Experimental Proof ◽  
Surface Boundary Layer ◽  
Pitch Moment ◽  
The Mean ◽  
High Reynolds

Abstract The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

scholarly journals Intermittency, Moments, and Friction Coefficient during the Subcritical Transition of Channel Flow

Entropy ◽  
2020 ◽  
Vol 22 (12) ◽  
pp. 1399
Author(s):  
Jinsheng Liu ◽  
Yue Xiao ◽  
Mogeng Li ◽  
Jianjun Tao ◽  
Shengjin Xu
Keyword(s):  
Friction Coefficient ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Test Case ◽  
Structure Model ◽  
Turbulent Structures ◽  
Third Order ◽  
Low Reynolds Numbers ◽  
The Third ◽  
High Turbulence

The intermittent distribution of localized turbulent structures is a key feature of the subcritical transitions in channel flows, which are studied in this paper with a wind channel and theoretical modeling. Entrance disturbances are introduced by small beads, and localized turbulent patches can be triggered at low Reynolds numbers (Re). High turbulence intensity represents strong ability of perturbation spread, and a maximum turbulence intensity is found for every test case as Re ≥ 950, where the turbulence fraction increases abruptly with Re. Skewness can reflect the velocity defects of localized turbulent patches and is revealed to become negative when Re is as low as about 660. It is shown that the third-order moments of the midplane streamwise velocities have minima, while the corresponding forth-order moments have maxima during the transition. These kinematic extremes and different variation scenarios of the friction coefficient during the transition are explained with an intermittent structure model, where the robust localized turbulent structure is simplified as a turbulence unit, a structure whose statistical properties are only weak functions of the Reynolds number.

Wind-tunnel experiments and separation control of a NACA4412 with 25○sweep at high Reynolds numbers

2022 ◽  
Author(s):  
Pierre-Yves Passaggia ◽  
Guillermo Lopez Quesada ◽  
Stéphane Loyer ◽  
Lucien Baldas ◽  
Jean-Christophe Robinet ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Reynolds Numbers ◽  
Separation Control ◽  
Wind Tunnel Experiments ◽  
High Reynolds Numbers ◽  
High Reynolds

Temperature Control of Blow-Down, Supersonic Tunnels

1956 ◽  
Vol 60 (541) ◽  
pp. 67-70
Author(s):  
T. A. Thomson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Stagnation Temperature ◽  
Blow Down ◽  
High Reynolds Numbers ◽  
Experimental Errors ◽  
High Reynolds

The blow-down type of intermittent, supersonic tunnel is attractive because of its simplicity and because relatively high Reynolds numbers can be obtained for a given size of test section. An adverse characteristic, however, is the fall of stagnation temperature during runs, which can affect experiments in several ways. The Reynolds number varies and the absolute velocity is not constant, even if the Mach number and pressure are; heat-transfer cannot be studied under controlled conditions and the experimental errors arising from the effect of heat-transfer on the boundary layer vary in time. These effects can become significant in quantitative experiments if the tunnel is large and the variation of temperature very rapid; the expense required to eliminate them might then be justified.

Reynolds Number Effects on the Freewheeling Behavior of a High Solidity Vertical River Kinetic Turbine

2010 ◽  
Author(s):  
Amir Hossein Birjandi ◽  
Eric Bibeau
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Speed Ratio ◽  
Stream Velocity ◽  
Blade Profile ◽  
Low Reynolds Numbers ◽  
Tip Speed Ratio ◽  
Reynolds Number Effects ◽  
High Reynolds ◽  
The University

A four-bladed, squirrel-cage, and scaled vertical kinetic turbine was designed, instrumented and tested in the water tunnel facilities at the University of Manitoba. With a solidity of 1.3 and NACA0021 blade profile, the turbine is classified as a high solidity model. Results were obtained for conditions during freewheeling at various Reynolds numbers. In this study, the freewheeling tip speed ratio, which relates the ratio of maximum blade speed to the free stream velocity at no load, was divided into three regions based on the Reynolds number. At low Reynolds numbers, the tip speed ratio was lower than unity and blades were in a stall condition. At the end of the first region, there was a sharp increase of the tip speed ratio so the second region has a tip speed ratio significantly higher than unity. In this region, the tip speed ratio increases almost linearly with Reynolds number. At high Reynolds numbers, the tip speed ratio is almost independent of Reynolds number in the third region. It should be noted that the transition between these three regions is a function of the blade profile and solidity. However, the three-region behavior is applicable to turbines with different profiles and solidities.

Stability of non-parabolic flow in a flexible tube

1999 ◽  
Vol 395 ◽  
pp. 211-236 ◽  
Author(s):  
V. SHANKAR ◽  
V. KUMARAN
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Asymptotic Analysis ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Flexible Tube ◽  
Developing Flow ◽  
Parabolic Flow ◽  
High Reynolds ◽  
The Stability

Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such ‘non-parabolic’ flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.

Turbulent Annular Pipe Flow in Subcritical Transition Regime: Direct Numerical Simulation of a Large Domain

2015 ◽  
Author(s):  
Takahiro Ishida ◽  
Takahiro Tsukahara
Keyword(s):  
Reynolds Number ◽  
Poiseuille Flow ◽  
Reynolds Numbers ◽  
Radius Ratio ◽  
Transition Regime ◽  
Transitional Regime ◽  
Large Domain ◽  
High Reynolds ◽  
Annular Pipe ◽  
Transition Scenario

We performed direct numerical simulations of annular Poiseuille flow (APF) with a radius ratio of η (= rin/rout) = 0.8, in order to investigate the subcritical transition scenario from the developed turbulent state to the laminar state. In previous studies on annular Poiseuille flow, the flows at high Reynolds numbers were well examined and various turbulence statistics were obtained for several η, because of their dependence on η. Since the transitional APF is still unclear, we investigate annular Poiseuille flows in the transitional regime through the large-domain simulations in a range of the friction Reynolds number from Reτ = 150 down to 56. At a transitional Reynolds number, weak-fluctuation regions occur intermittently and regularly in the flow field, and the localized turbulence appears in the form of banded patterns same as in plane Poiseuille flow (PPF). The flow system of APF with a high radius ratio η ≈ 1 can be regarded as PPF and, hence, the transition regime in high radius-ratio of APF and in PPF should be analogous. However, in APF, the banded structure takes on helical shape around the inner cylinder, since APF is a closed system in the spanwise (azimuthal) direction. In this paper, the (dis-)similarity between APF and PPF is discussed.

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