scholarly journals Flow Structure in a Rayleigh-Be´nard Cell Upon Impulsive Spin-Up

1998 ◽  
Vol 120 (4) ◽  
pp. 672-675
Author(s):  
Peter Vorobieff ◽  
Robert E. Ecke
Keyword(s):  
Regular Structure ◽  
Field Measurements ◽  
Vertical Axis ◽  
Thermochromic Liquid Crystal ◽  
Rotation Rates ◽  
Irregular Pattern ◽  
Image Velocimetry ◽  
Azimuthal Shear ◽  
Transient Feature ◽  
Steady Rotation

We investigate convection in a cylindrical Rayleigh-Be´nard cell with radius-to-height ratio Γ = 1/2. The cell is subjected to impulsive spin-up about its vertical axis. We use TLC (thermochromic liquid crystal) imaging for temperature field measurements and PIV (particle image velocimetry) for velocity reconstruction of the transition in the range of Rayleigh numbers R from 5 × 107 to 5 × 108 and dimensionless rotation rates Ω from 0 up to 8 × 104. The initial (at rest) and the final (in steady rotation) states of the system are those of turbulent convection. The most persistent transient feature is a well-defined ring pattern characterized by a decrease in temperature, axial velocity directed downward and high azimuthal shear. The latter leads to formation of an azimuthally regular structure of Kelvin-Helmholz vortices. During the final stage of the transition, this vortical structure loses azimuthal regularity and an irregular pattern of vortices characteristic of turbulent rotating convection forms.

Turbulent rotating convection: an experimental study

2002 ◽  
Vol 458 ◽  
pp. 191-218 ◽  
Author(s):  
PETER VOROBIEFF ◽  
ROBERT E. ECKE
Keyword(s):  
Circulation Pattern ◽  
Vertical Axis ◽  
Temperature Fields ◽  
Convection Cell ◽  
Vortex Sheets ◽  
Rotation Rates ◽  
Global Circulation ◽  
Steady Rotation ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

We present experimental measurements of velocity and temperature fields in horizontal planes crossing a cylindrical Rayleigh–Bénard convection cell in steady rotation about its vertical axis. The range of dimensionless rotation rates Ω is from zero to 5×104 for a Rayleigh number R = 3.2×108. The corresponding range of convective Rossby numbers is ∞ > Ro > 0.06. The patterns of velocity and temperature and the flow statistics characterize three basic flow regimes. For Ro [Gt ] 1, the flow is dominated by vortex sheets (plumes) typical of turbulent convection without rotation. The flow patterns for Ro ∼ 1 are cyclone-dominated, with anticyclonic vortices rare. As the Rossby number continues to decrease, the number of anticyclonic vortex structures begins to grow but the vorticity PDF in the vicinity of the top boundary layer still shows skewness favouring cyclonic vorticity. Velocity-averaging near the top of the cell suggests the existence of a global circulation pattern for Ro [Gt ] 1.

Characteristics of a separated flow past a semicircular leading-edge airfoil model under different imposed pressure gradient

2021 ◽  
pp. 095441002110212
Author(s):  
K Anand ◽  
KT Ganesh
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Particle Image ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Field Measurements ◽  
Bench Mark ◽  
Image Velocimetry

The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

Endoscopic 2D particle image velocimetry (PIV) flow field measurements in IC engines

2002 ◽  
Vol 33 (6) ◽  
pp. 794-800 ◽  
Author(s):  
U. Dierksheide ◽  
P. Meyer ◽  
T. Hovestadt ◽  
W. Hentschel
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Field Measurements ◽  
Image Velocimetry ◽  
Ic Engines

Stability of steady rotation of a rotor about its vertical axis on hydrodynamic bearings

1987 ◽  
Vol 23 (12) ◽  
pp. 1189-1195
Author(s):  
N. V. Derendyaev ◽  
V. A. Senyatkin ◽  
V. M. Sandalov
Keyword(s):  
Vertical Axis ◽  
Hydrodynamic Bearings ◽  
Steady Rotation

Improvement of Micro-PIV Resolution by Selective Seeding

2006 ◽  
Author(s):  
Michal M. Mielnik ◽  
Lars R. Sætran
Keyword(s):  
Optical Measurement ◽  
Fluid Layer ◽  
Field Measurements ◽  
Time Resolved ◽  
Micro Piv ◽  
Tracer Particles ◽  
Seeding Method ◽  
Image Velocimetry ◽  
Out Of Plane ◽  
Measurement Depth

A novel seeding method, permitting high out-of-plane resolution and instantaneous (time-resolved) velocity field measurements using a standard Microscale Particle Image Velocimetry (micro-PIV) setup, is presented. The method relies on selective seeding of a thin fluid layer within an otherwise particle-free flow. The generated particle sheet defines the depth and position of the measurement plane, independently of the details of the optical setup. Therefore, for low magnification objectives in particular, considerable improvement in the measurement depth is possible. Selectively seeded micro-PIV (SeS-PIV) is applied to a microchannel flow, and the measured instantaneous velocity fields are in excellent agreement with the theoretical solution for the flowfield. The currently presented measurements have a depth-wise resolution 20% below the estimated optical measurement depth of the micro-PIV system. In principle, a measurement depth corresponding to the diameter of the tracer particles may be achieved.

Analysis of Particle Image Velocimetry Measurements of Natural Convection in an Enclosure Using Proper Orthogonal Decomposition

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Nirmalendu Biswas ◽  
Souvick Chatterjee ◽  
Mithun Das ◽  
Amlan Garai ◽  
Prokash C. Roy ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Natural Convection ◽  
Velocity Field ◽  
Proper Orthogonal Decomposition ◽  
Particle Image ◽  
Field Measurements ◽  
Orthogonal Decomposition ◽  
Image Velocimetry ◽  
Low Dimensional ◽  
Proper Orthogonal

This work investigates natural convection in an enclosure with localized heating on the bottom wall with a flushed or protruded heat source and cooled on the top and the side walls. Velocity field measurements are done by using 2D particle image velocimetry (PIV) technique. Proper orthogonal decomposition (POD) has been used to create low dimensional approximations of the system for predicting the flow structures. The POD-based analysis reveals the modal structure of the flow field and also allows reconstruction of velocity field at conditions other than those used in PIV study.

Velocity Field Measurements in Leading Edge Wing Compartments

2008 ◽  
Author(s):  
V. Egan ◽  
D. T. Newport ◽  
V. Larcarac ◽  
B. Estebe
Keyword(s):  
Natural Convection ◽  
Leading Edge ◽  
Field Measurements ◽  
Dominant Mode ◽  
Fluid Temperature ◽  
Velocity Measurements ◽  
Thermal Boundary Conditions ◽  
Single Compartment ◽  
Image Velocimetry ◽  
Convection Cooling

For many applications the optimisation of natural convection cooling is a major design consideration due to factors such as weight, accessibility, cost and power consumption. In aircraft wing compartments, natural convection is the dominant mode of heat transfer due to high wall temperatures resulting from solar loading and heat dissipating internal electronics. This paper investigates the flow structures in a leading edge compartment subject to various thermal boundary conditions. The experimental configuration consisted of two leading edge enclosures; the first is a single compartment while the second has an attached wing box. Particle image velocimetry (PIV) was employed to obtain velocity measurements of the flow in both leading edge enclosures. The second compartment investigated the effect of an adjacent fluid filled enclosure on the flow regime in the leading edge compartment. Higher local velocities were found in the second compartment due to an increase in buoyancy forces resulting from a lower of the average fluid temperature within the compartment. The introduction of a heat dissipating component gave rise to two separate convection structures and in general increased the fluctuations in the both temperature and velocities within the compartment.

Flow Pattern Measurements by µ-PIV in the Microchannels of a Heat Exchanger and Solutions to the Particle Fouling Problem

2004 ◽  
Author(s):  
V. Heinzel ◽  
A. Jianu ◽  
H. Sauter
Keyword(s):  
Heat Exchanger ◽  
Particle Image ◽  
Field Measurements ◽  
Velocity Fields ◽  
Particle Image Velocimetry System ◽  
The Past ◽  
Image Velocimetry ◽  
Test Loop ◽  
Transparent Liquid ◽  
Flat Cell

Preliminary experimental results of measuring velocity fields of a transparent liquid flow in a closed circuit, through a 100 μm deep flat cell with heat exchanger microchannel elements are presented. The resolution and possible errors of the microscopic particle image velocimetry system are discussed in relation with the evaluation results. Particle fouling phenomenon, which proved to be the main difficulty in performing velocity field measurements in microchannels in the past, are widely overcome by techniques which avoid or limit it. The test object, which is aimed at being exposed to real technical conditions (pressures up to 0.6 MPa leading to flow velocities up to 15 m/s, as well as temperatures up to 100°C), was up to now operated at a Reynolds number of about 5. The obtained information allows for starting the test loop upgrade.

Aerothermal Investigation of a Single Row Divergent Narrow Impingement Channel by Particle Image Velocimetry and Liquid Crystal Thermography

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Alexandros Terzis ◽  
Christoforos Skourides ◽  
Peter Ott ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Particle Image Velocimetry ◽  
Liquid Crystal ◽  
Flow Field ◽  
Particle Image ◽  
Field Measurements ◽  
Single Row ◽  
Transient Techniques ◽  
Liquid Crystal Thermography ◽  
Image Velocimetry

Integrally cast turbine airfoils with wall-integrated cooling cavities are greatly applicable in modern turbines providing enhanced heat exchange capabilities compared to conventional cooling passages. In such arrangements, narrow impingement channels can be formed where the generated crossflow is an important design parameter for the achievement of the desired cooling efficiency. In this study, a regulation of the generated crossflow for a narrow impingement channel consisting of a single row of five inline jets is obtained by varying the width of the channel in the streamwise direction. A divergent impingement channel is therefore investigated and compared to a uniform channel of the same open area ratio. Flow field and wall heat transfer experiments are carried out at engine representative Reynolds numbers using particle image velocimetry (PIV) and liquid crystal thermography (LCT). The PIV measurements are taken at planes normal to the target wall along the centerline for each individual jet, providing quantitative flow visualization of jet and crossflow interactions. The heat transfer distributions on the target plate of the channels are evaluated with transient techniques and a multilayer of liquid crystals (LCs). Effects of channel divergence are investigated combining both the heat transfer and flow field measurements. The applicability of existing heat transfer correlations for uniform jet arrays to divergent geometries is also discussed.

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