scholarly journals The effects of obstacle shape and viscosity in deep rotating flow over finite-height topography

1982 ◽  
Vol 120 ◽  
pp. 359-383 ◽  
Author(s):  
E. R. Johnson
Keyword(s):  
Reynolds Number ◽  
Strong Dependence ◽  
Finite Depth ◽  
Reynolds Numbers ◽  
Rotating Flows ◽  
Rotating Flow ◽  
Rossby Number ◽  
Ridge Width ◽  
Inertial Wave ◽  
Finite Slope

The limiting process introduced by Stewartson & Cheng (1979) is used to obtain solutions in the limit of vanishing Rossby number for deep rotating flows at arbitrary Reynolds number over cross-stream ridges of finite slope. Examination of inviscid solutions for infinite-depth flow shows strong dependence on obstacle shape of not only the magnitudes but also the positions of disturbances in the far field. In finite-depth flow there is present the Stewartson & Cheng inertial wave wake, which may be expressed as a sum of vertical modes whose amplitudes depend on the obstacle shape but are independent of distance downstream; the smoother the topography and the shallower the flow, the fewer the number of modes required to describe the motion. For abrupt topography the strength of the wake does not, however, decrease monoton- ically with decreasing container depth (or Rossby number). In very deep flows viscosity causes the wake to decay on a length scale of order the Reynolds number times the ridge width. In shallower flows, where only a few modes are present, the decay of the wake is more rapid. For Reynolds numbers and depths of the order of those in the experiments of Hide, Ibbetson & Lighthill (1968)) viscosity causes the disturbance to take on the appearance of a leaning column.

scholarly journals Fluctuations of the non-Newtonian fluid flow in a Kenics static mixer: An experimental study

2008 ◽  
Vol 10 (3) ◽  
pp. 35-37 ◽  
Author(s):  
Sylwia Peryt-Stawiarska ◽  
Zdzisław Jaworski
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Newtonian Fluid ◽  
Strong Dependence ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Test Fluid ◽  
Static Mixer ◽  
Flow Fluctuations

Fluctuations of the non-Newtonian fluid flow in a Kenics static mixer: An experimental study The measurements for a Kenics static mixer were carried out using Laser Doppler Anemometer (LDA). The test fluid was non-Newtonian solution of CMC, Blanose type 9H4. The velocity data inside the 5th Kenics insert were collected for the axial components at five levels of Reynolds number, Re = 20 ÷ 120. Velocity fluctuations were also analyzed in the frequency domain, after processing them with the help of the Fast Fourier Transform (FFT) procedure. The spectra of fluctuations provided information about level of the fluctuations in the observed range of Reynolds number. The obtained data were then also used to plot the velocity profiles for the fifth insert of the Kenics mixer. It was concluded that in the investigated range of Reynolds numbers (Re = 20 ÷ 120) a strong dependence of the velocity profiles and the flow fluctuations on Reynolds number was observed.

Effects of Jet-to-Target Plate Distance and Reynolds Number on Jet Array Impingement Heat Transfer

2013 ◽  
Author(s):  
Junsik Lee ◽  
Zhong Ren ◽  
Jacob Haegele ◽  
Geoff Potts ◽  
Jae Sik Jin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Strong Dependence ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Stagnation Points ◽  
Nusselt Numbers ◽  
Impingement Heat Transfer ◽  
Plate Distance

Data which illustrate the effects of jet-to-target plate distance and Reynolds number on the heat transfer from an array of jets impinging on a flat plate are presented. Considered are Reynolds numbers Rej ranging from 8,200, to 52,000, with isentropic jet Mach numbers of approximately 0.1 to 0.2. Jet-to-target plate distances Z of 1.5D, 3.0D, 5.0D, and 8.0D are employed, where D is the impingement hole diameter. Steamwise and spanwise hole spacings are 8D. Local and spatially-averaged Nusselt numbers show strong dependence on the impingement jet Reynolds number for all situations examined. Experimental results also illustrate the dependence of local Nusselt numbers on normalized jet-to-target plate distance, especially for smaller values of this quantity. The observed variations are partially due to accumulating cross-flows produced as the jets advect downstream, as well as the interactions of the vortex structures which initially form around the jets, and then impact and interact as they advect away from stagnation points along the impingement target surface. The highest spatially-averaged Nusselt numbers are present for Z/D = 3.0 for Rej of 8,200, 20,900, and 30,000. When Rej = 52,000, spatially-averaged Nusselt numbers increase as Z/D decreases, with the highest value present at Z/D = 1.5.

A Numerical Study on Motion of a Sphere Coated With a Thin Liquid Film at Intermediate Reynolds Numbers

1997 ◽  
Vol 119 (2) ◽  
pp. 397-403 ◽  
Author(s):  
S. Kawano ◽  
H. Hashimoto
Keyword(s):  
Reynolds Number ◽  
Liquid Film ◽  
Drag Coefficient ◽  
Flow Pattern ◽  
Numerical Study ◽  
Thin Liquid Film ◽  
Strong Dependence ◽  
Reynolds Numbers ◽  
Rigid Sphere ◽  
Flow Past A Sphere

The steady viscous flow past a sphere coated with a thin liquid film at low and intermediate Reynolds numbers (Re ≤ 200) was investigated numerically. The influences of fluid physical properties, film thickness, and Reynolds number on the flow pattern were clarified. Temperature field around the compound drop was also analyzed. The strong dependence of flow pattern on the characteristics of heat transfer was recognized. The empirical equation of the drag coefficient for the compound drop was proposed. Furthermore, the explicit adaptability of the drag coefficient equation for a gas bubble, a liquid drop, and a rigid, sphere in the range of Reynolds number Re ≤ 1000 was confirmed.

scholarly journals Clean versus contaminated bubbles in a solid-body rotating flow

2017 ◽  
Vol 831 ◽  
pp. 592-617 ◽  
Author(s):  
Marie Rastello ◽  
Jean-Louis Marié ◽  
Michel Lance
Keyword(s):  
Solid Body ◽  
Lift Force ◽  
Rotating Flows ◽  
Rotating Flow ◽  
Rossby Number ◽  
Dynamical Equations ◽  
Drag And Lift Coefficients ◽  
New Information ◽  
Rear Part ◽  
Drag And Lift

The behaviour of clean and contaminated bubbles in solid-body rotating flows is compared in terms of drag and lift forces. Both spherical and deformed bubbles are considered. For that comparison, we have completed the data published in Rastello et al. (J. Fluid Mech., vol. 624, 2009, pp. 159–178; J. Fluid Mech., vol. 682, 2011, pp. 434–459) by a new series of measurements. When they are contaminated, bubbles are subject to an additional lift force due to the spinning of their surfaces, while the clean ones are not. A detailed description of this spinning motion is presented and an expression for the Magnus-like lift it induces is given in the light of the new information. The component of the lift induced by flow rotation depends on the Rossby number $Ro$, contrary to the case of clean bubbles. Including the ‘spin’ induced lift component in the dynamical equations provides a better prediction of the bubble’s trajectory in contaminated fluid. The presence of contaminants immobilizes the rear part of the bubble and reduces significantly the deformation. The laws of deformation according to the nature of the surface are presented. The way deformation influences the drag and lift coefficients in pure and contaminated fluids is quantified and discussed. Expressions for these various coefficients are proposed.

Effects of Jet-To-Target Plate Distance and Reynolds Number on Jet Array Impingement Heat Transfer

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Junsik Lee ◽  
Zhong Ren ◽  
Jacob Haegele ◽  
Geoffrey Potts ◽  
Jae Sik Jin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Strong Dependence ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Stagnation Points ◽  
Nusselt Numbers ◽  
Impingement Heat Transfer ◽  
Plate Distance

Data which illustrate the effects of jet-to-target plate distance and Reynolds number on the heat transfer from an array of jets impinging on a flat plate are presented. Considered are Reynolds numbers Rej ranging from 8200 to 52,000 with isentropic jet Mach numbers of approximately 0.1 to 0.2. Jet-to-target plate distances Z of 1.5D, 3.0D, 5.0D, and 8.0D are employed, where D is the impingement hole diameter. Streamwise and spanwise hole spacings are 8D. Local and spatially-averaged Nusselt numbers show strong dependence on the impingement jet Reynolds number for all situations examined. Experimental results also illustrate the dependence of local Nusselt numbers on normalized jet-to-target plate distance, especially for smaller values of this quantity. The observed variations are partially due to accumulating cross-flows produced as the jets advect downstream, as well as the interactions of the vortex structures, which initially form around the jets and then impact and interact as they advect away from stagnation points along the impingement target surface. The highest spatially-averaged Nusselt numbers are present for Z/D = 3.0 for Rej of 8200, 20,900, and 30,000. When Rej = 52,000, spatially-averaged Nusselt numbers increase as Z/D decreases, with the highest value present at Z/D = 1.5.

Inertial waves above an obstacle in an unbounded, rapidly rotating fluid

1982 ◽  
Vol 383 (1784) ◽  
pp. 71-87 ◽  
Keyword(s):  
Strong Dependence ◽  
Reynolds Numbers ◽  
Wave Pattern ◽  
Transverse Motion ◽  
Rotating Fluid ◽  
Vertical Scale ◽  
Internal Dissipation ◽  
Precise Shape ◽  
Inertial Wave ◽  
The Fourier Transform

The slow transverse motion of an obstacle of horizontal dimension L , in a rapidly rotating flow (such that the Rossby number, Ro , is small), is shown to cause an inertial-wave disturbance above and behind the obstacle. This disturbance spreads over an ever-increasing downstream region with increasing vertical distance above the obstacle, but is constrained laterally to lie within a wedge-shaped region. The discussion of Cheng (1977) is shown to give the diffraction pattern due to a point source, and his analysis is modified to allow for arbitrary obstacle shapes. Such a modification shows that the amplitude of the disturbance decays downstream at a rate deter­mined by the Fourier transform of the obstacle shape as noted by Johnson (1982) for ridge-like topography. The inclusion of viscosity is shown to damp out the disturbance on a vertical scale of L/Ek (where Ek = v /2 ΩL 2 is an Ekman number for the flow). At moderate Reynolds numbers visco­sity reduces the amplitude of the disturbance in the neighbourhood of the caustic at the wedge boundary, the attenuation increasing with distance downstream. Internal dissipation removes the short-wavelength com­ponents of the disturbance and thus removes the strong dependence of the wave pattern on the precise shape of the obstacle.

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.

scholarly journals Turbulence model performance for ventilation components pressure losses

2021 ◽  
Author(s):  
Karsten Tawackolian ◽  
Martin Kriegel
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Pressure Loss ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Test Case ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Near Wall

AbstractThis study looks to find a suitable turbulence model for calculating pressure losses of ventilation components. In building ventilation, the most relevant Reynolds number range is between 3×104 and 6×105, depending on the duct dimensions and airflow rates. Pressure loss coefficients can increase considerably for some components at Reynolds numbers below 2×105. An initial survey of popular turbulence models was conducted for a selected test case of a bend with such a strong Reynolds number dependence. Most of the turbulence models failed in reproducing this dependence and predicted curve progressions that were too flat and only applicable for higher Reynolds numbers. Viscous effects near walls played an important role in the present simulations. In turbulence modelling, near-wall damping functions are used to account for this influence. A model that implements near-wall modelling is the lag elliptic blending k-ε model. This model gave reasonable predictions for pressure loss coefficients at lower Reynolds numbers. Another example is the low Reynolds number k-ε turbulence model of Wilcox (LRN). The modification uses damping functions and was initially developed for simulating profiles such as aircraft wings. It has not been widely used for internal flows such as air duct flows. Based on selected reference cases, the three closure coefficients of the LRN model were adapted in this work to simulate ventilation components. Improved predictions were obtained with new coefficients (LRNM model). This underlined that low Reynolds number effects are relevant in ventilation ductworks and give first insights for suitable turbulence models for this application. Both the lag elliptic blending model and the modified LRNM model predicted the pressure losses relatively well for the test case where the other tested models failed.

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

scholarly journals Thermoelectric Generation with Impinging Nano-Jets

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 492
Author(s):  
Fatih Selimefendigil ◽  
Hakan F. Oztop ◽  
Mikhail A. Sheremet
Keyword(s):  
Fluid Dynamics ◽  
Power Generation ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Conversion Efficiency ◽  
Reynolds Numbers ◽  
Thermoelectric Generation ◽  
Volume Fractions ◽  
Water Jets ◽  
Conversion Efficiencies

In this study, thermoelectric generation with impinging hot and cold nanofluid jets is considered with computational fluid dynamics by using the finite element method. Highly conductive CNT particles are used in the water jets. Impacts of the Reynolds number of nanojet stream combinations (between (Re1, Re2) = (250, 250) to (1000, 1000)), horizontal distance of the jet inlet from the thermoelectric device (between (r1, r2) = (−0.25, −0.25) to (1.5, 1.5)), impinging jet inlet to target surfaces (between w2 and 4w2) and solid nanoparticle volume fraction (between 0 and 2%) on the interface temperature variations, thermoelectric output power generation and conversion efficiencies are numerically assessed. Higher powers and efficiencies are achieved when the jet stream Reynolds numbers and nanoparticle volume fractions are increased. Generated power and efficiency enhancements 81.5% and 23.8% when lowest and highest Reynolds number combinations are compared. However, the power enhancement with nanojets using highly conductive CNT particles is 14% at the highest solid volume fractions as compared to pure water jet. Impacts of horizontal location of jet inlets affect the power generation and conversion efficiency and 43% variation in the generated power is achieved. Lower values of distances between the jet inlets to the target surface resulted in higher power generation while an optimum value for the highest efficiency is obtained at location zh = 2.5ws. There is 18% enhancement in the conversion efficiency when distances at zh = ws and zh = 2.5ws are compared. Finally, polynomial type regression models are obtained for estimation of generated power and conversion efficiencies for water-jets and nanojets considering various values of jet Reynolds numbers. Accurate predictions are obtained with this modeling approach and it is helpful in assisting the high fidelity computational fluid dynamics simulations results.

Sign in / Sign up

Export Citation Format

Share Document