Turbulent Flow in a Rotating Two Pass Ribbed Rectangular Channel

2003 ◽  
Vol 125 (4) ◽  
pp. 609-622 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Hsiang-Jung Chin
Keyword(s):  
Laser Doppler Anemometry ◽  
Rectangular Cross Section ◽  
Rectangular Channel ◽  
Stress Distributions ◽  
Centrifugal Forces ◽  
Reattachment Length ◽  
Mean Velocity ◽  
Stream Flows ◽  
Measured Flow ◽  
Turbulent Air Flow

Laser-Doppler anemometry has been applied to approximately two-dimensional turbulent air flow in rotating two pass channel with turbulator of rectangular cross section (AR=3:1). The axis of rotation is normal to the axis of the duct, and the flow is radially outward/inward. The duct is of finite length and the walls are isothermal. Two sided oppositely ribbed channel including one sided ribbed U bend of p/e=8 at e/DH=0.27 are experimentally conducted with ReD=5000 and 10,000. The main features of the flow, reattachment length, recirculation zone, and mean velocity as well as turbulent intensity and shear stress distributions are presented in ribbed ducts. The measured flow field is found to be quite complex, consisting of secondary cross-stream flows due to the Coriolis effects and centrifugal forces with rib-roughened surfaces.

Turbulent Flow in a Rotating Two Pass Smooth Channel

1999 ◽  
Vol 121 (4) ◽  
pp. 725-734 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Ping-Ju Chen ◽  
Hsiang-Jung Chin
Keyword(s):  
Flow Field ◽  
Cross Section ◽  
Flow Separation ◽  
Laser Doppler Anemometry ◽  
Centrifugal Forces ◽  
Mean Velocity ◽  
Axis Of Rotation ◽  
Smooth Channel ◽  
Measured Flow ◽  
Turbulent Air Flow

Laser-Doppler anemometry has been applied to approximately 2-D turbulent air flow in a rotating 2 pass channel of square cross section. The axis of rotation is normal to the axis of the duct, and the flow is radially outward/inward. The duct is of finite length and the walls are isothermal. Smooth channels are experimentally conducted with rotational speeds of 100, 200, and 300 rpm with ReH = 5000 and 10,000. The main features of the flow, flow separation and mean velocity as well as turbulent intensity at particular location along the downstream are presented. The measured flow field is found to be quite complex, consisting of secondary cross-stream and radially outward flows due to the Coriolis effects and centrifugal forces.

scholarly journals Urban Boundary Layers Over Dense and Tall Canopies

2021 ◽  
Author(s):  
Alexandros Makedonas ◽  
Matteo Carpentieri ◽  
Marco Placidi
Keyword(s):  
Packing Density ◽  
Laser Doppler Anemometry ◽  
Canopy Height ◽  
Roughness Sublayer ◽  
Average Height ◽  
Wind Tunnel Experiments ◽  
Mean Velocity ◽  
Flow Features ◽  
Stress Layer ◽  
Density Results

AbstractWind-tunnel experiments were carried out on four urban morphologies: two tall canopies with uniform height and two super-tall canopies with a large variation in element heights (where the maximum element height is more than double the average canopy height, $$h_{max}=2.5h_{avg}$$ h max = 2.5 h avg ). The average canopy height and packing density are fixed across the surfaces to $$h_{avg} = 80~\hbox {mm}$$ h avg = 80 mm , and $$\lambda _{p} = 0.44$$ λ p = 0.44 , respectively. A combination of laser Doppler anemometry and direct-drag measurements are used to calculate and scale the mean velocity profiles with the boundary-layer depth $$\delta $$ δ . In the uniform-height experiment, the high packing density results in a ‘skimming flow’ regime with very little flow penetration into the canopy. This leads to a surprisingly shallow roughness sublayer (depth $$\approx 1.15h_{avg}$$ ≈ 1.15 h avg ), and a well-defined inertial sublayer above it. In the heterogeneous-height canopies, despite the same packing density and average height, the flow features are significantly different. The height heterogeneity enhances mixing, thus encouraging deep flow penetration into the canopy. A deeper roughness sublayer is found to exist extending up to just above the tallest element height (corresponding to $$z/h_{avg} = 2.85$$ z / h avg = 2.85 ), which is found to be the dominant length scale controlling the flow behaviour. Results point toward the existence of a constant-stress layer for all surfaces considered herein despite the severity of the surface roughness ($$\delta /h_{avg} = 3 - 6.25$$ δ / h avg = 3 - 6.25 ). This contrasts with the previous literature.

scholarly journals Study of Pumping Capacity of Pitched Blade Impellers

10.14311/380 ◽  
2002 ◽  
Vol 42 (4) ◽  
Author(s):  
I. Fořt ◽  
T. Jirout ◽  
R. Sperling ◽  
S. Jambere ◽  
F. Rieger
Keyword(s):  
Laser Doppler Anemometry ◽  
Radial Profile ◽  
Axial Flow ◽  
Power Input ◽  
Vessel Diameter ◽  
Energetic Efficiency ◽  
Turbulent Regime ◽  
Flat Bottom ◽  
Mean Velocity ◽  
Liquid Suspensions

A study was made of the pumping capacity of pitched blade impellers in a cylindrical pilot plant vessel with four standard radial baffles at the wall under a turbulent regime of flow. The pumping capacity was calculated from the radial profile of the axial flow, under the assumption of axial symmetry of the discharge flow. The mean velocity was measured using laser Doppler anemometry in a transparent vessel of diameter T = 400 mm, provided with a standard dished bottom. Three and six blade pitched blade impellers (the pitch angle varied within the interval a Îá24°; 45°ń) of impeller/vessel diameter ratio D/T = 0.36, as well as a three blade pitched blade impeller with folded blades of the same diameter, were tested. The calculated results were compared with the results of experiments mentioned in the literature, above all in cylindrical vessels with a flat bottom. Both arrangements of the agitated system were described by the impeller energetic efficiency, i.e, a criterion including in dimensionless form both the impeller energy consumption (impeller power input) and the impeller pumping effect (impeller pumping capacity). It follows from the results obtained with various geometrical configurations that the energetic efficiency of pitched blade impellers is significantly lower for configurations suitable for mixing solid-liquid suspensions (low impeller off bottom clearances) than for blending miscible liquids in mixing (higher impeller off bottom clearances).

Numerical Study on the Effect of Bend Angle on Turbulent Flow through Oscillating Bend

2009 ◽  
Vol 4 (1) ◽  
Author(s):  
Elham Ameri ◽  
M Nasr Esfahany
Keyword(s):  
Numerical Study ◽  
Bend Angle ◽  
Curvature Radius ◽  
Primary Flow ◽  
Mean Velocity ◽  
Contour Map ◽  
Curved Pipes ◽  
Flow Through ◽  
The Mean ◽  
Turbulent Air Flow

The effect of the bend angle on the unsteady developing turbulent air flow through oscillating circular-sectioned curved pipes with the various angles of 180°, 135° and 90° was investigated numerically. The bends had a diameter of 106 mm and a curvature radius ratio of 6.0 with long, straight upstream and downstream sections. Results of the mean velocity and static pressure were obtained at a Reynolds number of 31200 and at various longitudinal stations. The velocity of the primary flow was illustrated in the form of contour map and vector diagram. From the inlet plane of the three oscillating bends to the angle of 45°, the velocity fields in 180°, 90° and 135° bends are similar. The high velocity regions, however, occur near the upper and lower parts in 90° and 180° bends, respectively.

Establishment of the Wake Behind a Disk

1964 ◽  
Vol 86 (4) ◽  
pp. 869-880 ◽  
Author(s):  
Thomas Carmody
Keyword(s):  
Shear Stress ◽  
Ambient Pressure ◽  
Continuous Distribution ◽  
Flow Characteristics ◽  
Graphical Form ◽  
Stress Distributions ◽  
Mean Velocity ◽  
Pressure Distributions ◽  
Energy Relationships ◽  
The Mean

An air-tunnel study of the establishment of the wake behind a disk at a Reynolds number of approximately 7 × 104 was undertaken. On the basis of the measured data, such a wake is fully established, that is, similarity profiles of the flow characteristics are formed, within 15 diameters of the disk, and approximately 95 percent of the transfer of energy from the mean motion to the turbulence motion takes place within 3 diameters of the disk, in the region of the mean standing eddy. The measured mean ambient-pressure and mean total-pressure distributions, mean velocity distributions, turbulence-intensity and shear-stress distributions, and the mean streamline pattern are presented in graphical form, as are the quantitative balances of the integrated momentum and mean-energy relationships. A stream function consisting of a continuous distribution of doublets is introduced to extend the radial limit of understanding of the flow characteristics to a very large if not infinite radius. Considerable attention is given to the problem of obtaining and interpreting turbulence shear-stress data immediately downstream from the point of flow separation. The applicability of a local diffusion coefficient or virtual viscosity of the Boussinesq or Prandtl type for relating the turbulence shear stress to the radial gradient of mean axial velocity is discussed. The Bernoulli sum and the energy changes along individual streamlines investigated in an associated study are incorporated herein to obtain a quantitative estimate of the local errors involved in the turbulence-shear-stress measurements.

Stress Distributions in Nonsymmetric Rotating Rays

1955 ◽  
Vol 22 (3) ◽  
pp. 311-316
Author(s):  
P. G. Hodge
Keyword(s):  
Plastic Deformation ◽  
Stress Distribution ◽  
Large Scale ◽  
Bending Moment ◽  
Rotating Disk ◽  
Longitudinal Force ◽  
Maximum Speed ◽  
Stress Distributions ◽  
Centrifugal Forces

Abstract The centrifugal forces acting upon a rotating ray will produce longitudinal stresses along the ray. If the ray is not symmetric, these stresses will result not only in a longitudinal force, but also in a bending moment. A technique for finding the stress distribution in this case is developed and illustrated by means of simple examples. The limiting elastic speed and the maximum speed before large-scale plastic deformation commences are computed. An indication is given of how similar methods may be used to analyze a rotating disk with no plane of symmetry perpendicular to the axis.

Aerodynamic Investigation of a Passive Secondary Jet Exciting a Separation Bubble for a Blunt Flat Plate

2015 ◽  
Author(s):  
Christian Helcig ◽  
Stefan aus der Wiesche ◽  
Stephan Uhkoetter
Keyword(s):  
Boundary Layer ◽  
Laser Doppler Anemometry ◽  
Separation Bubble ◽  
Flow Characteristics ◽  
Numerical Procedure ◽  
Large Eddy Simulations ◽  
Reattachment Length ◽  
Large Eddy ◽  
Low Speed Wind Tunnel ◽  
Aerodynamic Investigation

The aim of this study is to examine the influence of passive jets interacting with the separation region of the flow around a blunt plate. Experimental and numerical analysis are used to measure the velocity within the separation and reattachment region of the blunt plate with different passive jet configurations. A blunt plate was placed in a low speed wind tunnel to conduct Laser-Doppler anemometry (LDA) measurements at Re = 2.06 × 104. For the numerical procedure a dynamical sub-grid model for Large Eddy Simulations (LES) was used. For all configurations the flow characteristics such as the reattachment length were determined to characterize the boundary layer. The passive jets showed a strong influence by interacting with the boundary layer of the blunt plate.

Mechanical Properties and Experimental Study of a Composite Polishing Plate during Super-High Polishing

2010 ◽  
Vol 135 ◽  
pp. 337-342
Author(s):  
Li Zhou ◽  
Shu Tao Huang ◽  
Li Fu Xu
Keyword(s):  
Chemical Reaction ◽  
High Speed ◽  
Equivalent Stress ◽  
Stress Distributions ◽  
Centrifugal Forces ◽  
X Ray ◽  
High Speed Rotation ◽  
Speed Rotation ◽  
Von Mises Equivalent Stress ◽  
Von Mises

A new composite polishing plate for polishing of CVD diamond films has been designed. The displacement and stress distributions of the high speed rotation polishing plate have been investigated due to centrifugal forces, and the polishing mechanism of super-high polishing has been analyzed by using X-ray photo-electron spectroscopy. The results showed that the displacements both in axial and radial increase with the increasing of the rotational speed. When the rotation speed reached to 1200 rad/s, the von Mises equivalent stress is about 242 MPa, which is safe for the composite polishing plate. Additional, the polishing mechanism is mainly the chemical reaction between carbon and titanium during the super-high speed polishing. At elevated temperature, the chemical reaction between oxygen and titanium, oxygen and carbon can also occur.

Experimental and Numerical Characterization of the Flow Around the Keel of a Yacht

2008 ◽  
Author(s):  
Renata M. B. Chaves ◽  
Atila P. S. Freire ◽  
Alexandre T. P. Alho
Keyword(s):  
Laboratory Data ◽  
Turbulence Models ◽  
Detailed Comparison ◽  
Mean Velocity ◽  
Flow Parameters ◽  
Numerical Characterization ◽  
Sst Model ◽  
Order Of Magnitude ◽  
Measured Flow ◽  
Turbulence Data

The present work carries out a detailed comparison between numerical computations for the flow around the keel and the bulb of a sailboat and some newly obtained laboratory data. Two typical turbulence models are tested: the eddy-viscosity SST model and the second-moment model BSL-RSM-ω. Hot-wire anemometry (HWA) and particle image velocimetry (PIV) are used to characterize the flow around the keel and the bulb of a yacht. The experiments are conducted in a low speed wind tunnel. Measured flow parameters include the mean velocity profiles and second order moments. Both turbulence models are shown to perform well regarding mean velocity and global predictions. Turbulence data predictions, however, are shown to be erroneous by at least one order of magnitude.

scholarly journals Corner separation effects for normal shock wave/turbulent boundary layer interactions in rectangular channels

2012 ◽  
Vol 707 ◽  
pp. 287-306 ◽  
Author(s):  
D. M. F. Burton ◽  
H. Babinsky
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Laser Doppler Anemometry ◽  
Rectangular Channel ◽  
Wave Interaction ◽  
Adverse Pressure Gradient ◽  
Normal Shock ◽  
Corner Separation ◽  
Compression Waves ◽  
Boundary Layer Interaction

AbstractExperiments are conducted to examine the mechanisms behind the coupling between corner separation and separation away from the corner when holding a high-Mach-number ${M}_{\infty } = 1. 5$ normal shock in a rectangular channel. The ensuing shock wave interaction with the boundary layer on the wind tunnel floor and in the corners was studied using laser Doppler anemometry, Pitot probe traverses, pressure sensitive paint and flow visualization. The primary mechanism explaining the link between the corner separation size and the other areas of separation appears to be the generation of compression waves at the corner, which act to smear the adverse pressure gradient imposed upon other parts of the flow. Experimental results indicate that the alteration of the $\lambda $-region, which occurs in the supersonic portion of the shock wave/boundary layer interaction (SBLI), is more important than the generation of any blockage in the subsonic region downstream of the shock wave.

Sign in / Sign up

Export Citation Format

Share Document