The Mixing Characteristics of a Transverse Jet under Different Reynolds Number and Velocity Ratio

2011 ◽  
pp. 359-363
Author(s):  
Ling Zhongqian ◽  
Li Guoneng ◽  
Chen Mian
Keyword(s):  
Reynolds Number ◽  
Velocity Ratio ◽  
Transverse Jet ◽  
Mixing Characteristics

Active Flow Control of Dynamic Stall by Means of Continuous Jet Flow at Reynolds Number of 1 × 106

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Mehran Tadjfar ◽  
Ehsan Asgari
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Pressure Difference ◽  
Active Flow Control ◽  
Velocity Ratio ◽  
Dynamic Stall ◽  
Hysteresis Curve ◽  
Small Range ◽  
Active Flow ◽  
The Impact

We have studied the influence of a tangential blowing jet in dynamic stall of a NACA0012 airfoil at Reynolds number of 1 × 106, for active flow control (AFC) purposes. The airfoil was oscillating between angles of attack (AOA) of 5 and 25 deg about its quarter-chord with a sinusoidal motion. We have utilized computational fluid dynamics to investigate the impact of jet location and jet velocity ratio on the aerodynamic coefficients. We have placed the jet location upstream of the counter-clockwise (CCW) vortex which was formed during the upstroke motion near the leading-edge; we have also considered several other locations nearby to perform sensitivity analysis. Our results showed that placing the jet slot within a very small range upstream of the CCW vortex had tremendous effects on both lift and drag, such that maximum drag was reduced by 80%. There was another unique observation: placing the jet at separation point led to an inverse behavior of drag hysteresis curve in upstroke and downstroke motions. Drag in downstroke motion was significantly lower than upstroke motion, whereas in uncontrolled case the converse was true. Lift was significantly enhanced during both upstroke and downstroke motions. By investigating the pressure coefficients, it was found that flow control had altered the distribution of pressure over the airfoil upper surface. It caused a reduction in pressure difference between upper and lower surfaces in the rear part, while substantially increased pressure difference in the front part of the airfoil.

Numerical Simulation of Flow Past Multiple Porous Cylinders

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
M. H. Al-Hajeri ◽  
A. Aroussi ◽  
A. Witry
Keyword(s):  
Reynolds Number ◽  
Power Plants ◽  
Flow Behavior ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Solid Cylinder ◽  
Flow Past ◽  
Line Array ◽  
Face Velocity ◽  
Porous Cylinders

The present study numerically investigates two-dimensional laminar flow past three circular porous cylinders arranged in an in-line array. Six approaches to face velocity (Vi/Vf) ratios are used and particle trajectories are computed for a range of velocities and particle diameters. Furthermore, the flow past a solid cylinder, which had similar geometry characteristics to the porous cylinders used in this study, is compared with the flow around multiple porous cylinders. For the same range of Reynolds number (312–520), the flow behavior around the solid cylinder differs from the flow around the porous cylinders. The flow characteristics around solid cylinders are determined by the Reynolds number, whereas the flow characteristics around the porous cylinders are detrained by the Vi/Vf ratio. Stagnation areas are found behind each porous cylinder, and the size of these areas increases as the Vi/Vf velocity ratio increases. Furthermore, for the particle ranges used in power plants (<50 μm), the particles were uniformly distributed around the surface of the porous cylinders.

Turbulent Wake of a Stack and the Influence of Velocity Ratio

2006 ◽  
Author(s):  
M. S. Adaramola ◽  
D. Sumner ◽  
D. J. Bergstrom
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Reynolds Shear Stress ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Turbulent Wake ◽  
Mean Velocity ◽  
Distinct Structure ◽  
Flow Reynolds Number ◽  
Cross Flow Velocity

The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylindrical stack of AR = 9 was investigated with two-component thermal anemometry. The cross-flow Reynolds number was ReD = 2.3×104, the jet Reynolds number ranged from Red = 7×103 to 4.6×104, and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-height ratio of δ/H = 0.5 at the location of the stack. The flow around the stack was broadly classified into three flow regimes depending on the value of R, which were the downwash (R &lt; 0.5), cross-wind dominated (0.5 &lt; R &lt; 1.5), and jet-dominated (R &gt; 1.5) regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields.

Thermal Fluid Flow Transport Characteristics in Confined Channels With Two-Dimensional Dual Jet Impingement

2011 ◽  
Author(s):  
Caner Senkal ◽  
Shuichi Torii
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Inclination Angle ◽  
Transfer Rate ◽  
Velocity Ratio ◽  
Heated Wall ◽  
Outer Diameter ◽  
Stagnation Zone ◽  
Governing Equations

The flow and heat transfer characteristics of laminar dual circular jet impinging on a heating plate with inclined confinement surface has been investigated numerically. Governing equations in steady state are solved by a control volume based finite-difference method. The simulations have been carried out for Reynolds number (250≤Re≤418), the angle of inclination of the confined upper wall (0 ≤ θ ≤ 10), circular jet to annular jet velocity ratio (0≤VR≤2) and jet to target plate distances between 2D and 8D where D is the outer diameter of dual jet.SIMPLE algorithm was used to obtain velocity and temperature fields. Hybrid difference scheme is adopted for the discretized terms in the governing equations. The discretised equations are solved iteratively using the tridiagonal matrix algorithm line solver. Heat transfer performance along the heated wall is amplified with an increase in the velocity ratio and the Reynolds number. On the contrary, a substantial reduction in the heat transfer rate, for VR = 0.0, occurs in the stagnation zone, because the absence of the inner nozzle injection causes the recirculation in the corresponding region. The heat transfer rate in the stagnation zone is attenuated by increasing the jet nozzle to impinging plate distance. In particular, the effect of the inclination angle in the down-stream region, especially at the vicinity of outlet, is major then other effects Nusselt number distribution on the impingement plate is affected by inclined upper wall because inclination of the wall accelerates the exhaust flow. The streamwise reduction in the heat transfer rate for θ = 0° is suppressed by the presence of the inclined confinement surface and its value is intensified by the inclination angle.

scholarly journals Computation of heat transfer of a plane turbulent jet impinging a moving plate

2014 ◽  
Vol 18 (4) ◽  
pp. 1259-1271 ◽  
Author(s):  
Dahbia Benmouhoub ◽  
Amina Mataoui
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Field ◽  
Velocity Ratio ◽  
Local Heat Transfer ◽  
Slight Modification ◽  
Surface Velocity ◽  
Moving Plate ◽  
Jet Velocity

This study examines the performance of one point closure turbulence models in predicting of heat and momentum transfer of impinging flows. The scope of this paper is limited to impinging jet on a moving wall and heat transfer. The impinging distance is fixed to 8 thickness of the nozzle (8e) for this study. Two parameters are considered: the jet exit Reynolds number (10000?Re?25000) and the jet-surface velocity ratio (0?Rsj?4). the flow field structure at a given surface-to-jet velocity ratio is independent of the jet Reynolds number, a slight modification of the flow field is observed for low surface-to-jet velocity ratio (Rsj<0.25) whereas at higher ratios Rsj>0.25, the flow field is significantly modified. Good agreement with experimental results is obtained for surface-to-jet velocity ratio 0?Rsj?2. the purpose of this paper is to consider the case of higher of surface-to-jet velocity Rsj>2. A further study of heat transfer is achieved and shows that the stagnation points the local heat transfer coefficient have a maximum value. The local Nusselt number at the impinging region tends to decrease significantly when Rsj?1.5. The evolution of average Nusselt number is correlated according to the surface-to-jet velocity ratios for each Reynolds number.

Characterizing Pulsating Mixing of Slurries

2007 ◽  
Author(s):  
Judith Ann Bamberger ◽  
Perry A. Meyer
Keyword(s):  
Reynolds Number ◽  
Settling Velocity ◽  
Velocity Ratio ◽  
Applied Pressure ◽  
Pulse Tube ◽  
Operational Parameters ◽  
Hindered Settling ◽  
Jet Mixing ◽  
Pulse Jet ◽  
Pulse Jet Mixing

This paper describes the physical properties for defining the operation of a pulse jet mixing system. Pulse jet mixing systems operate with no moving parts located in the vessel or in the fluid to be mixed. Pulse tubes submerged in the vessel provide a pulsating flow that mixes the fluid due to a controlled combination of applied pressure to expel the fluid from the pulse tube nozzle followed by suction to refill the pulse tube through the same nozzle. For mixing slurries nondimensional parameters to define mixing operation include slurry properties, geometric properties and operational parameters. Primary parameters include jet Reynolds number and Froude number; alternate parameters may include particle Galileo number, particle Reynolds number, settling velocity ratio, and hindered settling velocity ratio. Rating metrics for system performance include just suspended velocity, concentration distribution as a function of elevation, and blend time.

Unsteady state fluid structure of two-sided nonfacing lid-driven cavity induced by a semicircle at different radii sizes and velocity ratios

2019 ◽  
Vol 30 (08) ◽  
pp. 1950060 ◽  
Author(s):  
Basma Souayeh ◽  
Fayçal Hammami ◽  
Najib Hdhiri ◽  
Huda Alfannakh
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Velocity Ratio ◽  
Time History ◽  
Standard Case ◽  
Driven Cavity ◽  
Opposite Case ◽  
Critical Reynolds Numbers ◽  
Volume Method ◽  
Radius Size

This paper aims in analyzing the effect of velocity ratio [Formula: see text] and Radius size of an inner semicircle inserted at the bottom wall of two-sided nonfacing lid-driven cavity on the bifurcation occurrence phenomena. The study has been performed by using finite volume method (FVM) and multigrid acceleration for certain pertinent parameters; Reynolds number, velocity ratios ([Formula: see text]) by step of 0.25 and Radius size of the inner semicircle ([Formula: see text]) by step of 0.05. An analysis of the flow evolution shows that, when increasing Re beyond a certain critical value, the flow becomes unstable then bifurcates for various velocity ratios and radius size of the semicircle. Therefore, critical Reynolds numbers are determined for each case. It is worth to mention that the transition to unsteadiness follows the classical scheme of a Hopf bifurcation. Results show also that in the standard case of a single lid-driven cavity ([Formula: see text]), the highest critical Reynolds number corresponds to the lowest radius of the semicircle and the same for ([Formula: see text]). Conversely, from ([Formula: see text]) where the left moving lid take effect, the opposite phenomenon occurs. In harmony with this, it has been found that elongating the cylinder radius accelerates the appearance of the unsteady regime and delays it in the opposite case. Flow periodicity has been verified through time history plots for the velocity component and phase-space trajectories as a function of Reynolds number. The numerical results are correlated in a sophisticated correlation of the critical Reynolds number with other parameters.

The Production of Duct Velocity Profiles Having High Ratios of Maximum to Mean Velocity

1956 ◽  
Vol 60 (546) ◽  
pp. 415-417 ◽  
Author(s):  
J. L. Livesey ◽  
E. Parker ◽  
P. K. Jones
Keyword(s):  
Reynolds Number ◽  
Incompressible Flow ◽  
Pressure Loss ◽  
Velocity Ratio ◽  
Velocity Profiles ◽  
Mean Velocity ◽  
Entry Length ◽  
Loss Coefficients

The results are presented of an investigation of a particular type of baffle for the production of symmetrical velocity profiles having high ratios of maximum to mean velocity in ducted incompressible flow. Two similar families of profiles are obtained depending on whether a short (12 diameters) or a long (48 diameters) entry length is used before the baffle. The highest value of the maximum to mean velocity ratio obtained is 1·42 and the pressure loss coefficients associated with the use of the baffle are given together with an indication of the effect of Reynolds number.

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