Separation and wake of pulsating laminar flow

1987 ◽  
Vol 322 (1568) ◽  
pp. 493-523 ◽  
Keyword(s):  
Laser Doppler Velocimetry ◽  
Large Scale ◽  
Natural Frequencies ◽  
Inviscid Flow ◽  
Wake Flow ◽  
Digital Data ◽  
Doppler Velocimetry ◽  
Hot Wire ◽  
Separated Shear Layer ◽  
Flow Visualizations

This is an experimental study of laminar pulsating flow that passes through separation and is led to a separated region. Detailed information is obtained on all interconnected regions, namely, the approaching attached laminar boundary layer, the immediate neighbourhood of separation, the separated shear layer, the large-scale vortical region of the wake and the outer inviscid flow. The approaching flow is pulsated with frequencies that include the natural frequencies of the wake. Flow visualizations are contrasted with instantaneous and averaged digital data obtained via laser-Doppler velocimetry and hot-wire anemometry. The interaction of the disturbing and natural frequencies is studied. Results are com pared with recent theoretical advances. It is found that the amplitude of the imposed disturbance grows sharply in the neighbourhood of separation.

Aerodynamic Measurements on the Interaction of Secondary Jets and Separation Bubble

2012 ◽  
Author(s):  
A. Samson ◽  
S. Sarkar
Keyword(s):  
Flat Plate ◽  
Large Scale ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Leading Edge ◽  
Bubble Interactions ◽  
Separated Shear Layer ◽  
Bubble Length ◽  
Flow Visualizations ◽  
Turbulence Generation

The dynamics of separation bubble under the influence of continuous jets ejected near the semi-circular leading edge of a flat plate is presented. Two different streamwise injection angles 30° and 60° and velocity ratios 0.5 and 1 for Re = 25000 and 55000 (based on the leading-edge diameter) are considered here. The flow visualizations illustrating jet and separated layer interactions have been carried out with PIV. The objective of this study is to understand the mutual interactions of separation bubble and the injected jets. It is observed that flow separates at the blending point of semi-circular arc and flat plate. The separated shear layer is laminar up to 20% of separation length after which perturbations are amplified and grows in the second-half of the bubble leading to breakdown and reattachment. Blowing has significantly affected the bubble length and thus, turbulence generation. Instantaneous flow visualizations supports the unsteadiness and development of three-dimensional motions leading to formation of Kelvin-Helmholtz rolls and shedding of large-scale vortices due to jet and bubble interactions. In turn, it has been seen that both the spanwise and streamwise dilution of injected air is highly influenced by the separation bubble.

scholarly journals Assessing the infinitely expanding intersection region for the development of large-scale multipoint laser Doppler velocimetry

2019 ◽  
Vol 70 ◽  
pp. 101660 ◽  
Author(s):  
Tomoaki Kyoden ◽  
Shunsuke Akiguchi ◽  
Tomoki Tajiri ◽  
Tsugunobu Andoh ◽  
Noriyuki Furuichi ◽  
...  
Keyword(s):  
Laser Doppler Velocimetry ◽  
Large Scale ◽  
Laser Doppler ◽  
Doppler Velocimetry

scholarly journals Laser Doppler Velocimetry Characterization of Unsteady Vaned Diffuser Flow in a Centrifugal Compressor

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
William J. Gooding ◽  
John C. Fabian ◽  
Nicole L. Key
Keyword(s):  
Centrifugal Compressor ◽  
Laser Doppler Velocimetry ◽  
High Speed ◽  
Pressure Rise ◽  
Laser Doppler ◽  
Wake Flow ◽  
Quality Data ◽  
Doppler Velocimetry ◽  
Design Development ◽  
Complex Flow

Abstract Modern turbomachinery faces increased performance demands in terms of efficiency, compactness, and pressure-rise. Advancements in computational technology have allowed numerical methods to become the backbone of design development efforts. However, the unique complexities of centrifugal compressor flow-fields pose difficult computational problems. As such, advanced experimental methods must be used to obtain high-quality data sets to further inform, improve, and validate computational methods in complex flow regimes. A recent experimental work on a high-speed centrifugal compressor has provided detailed, unsteady, three-component velocity data using laser Doppler velocimetry. A passage vortex is present, and its nascent tied to the increased incidence at mid-span associated with impeller wake flow. This vortex begins in the hub-pressure side corner and grows to fill the passage and become temporally stable. The vortex development is unsteady in nature, and the unsteady effects persist 40% downstream of the throat. Distinct jet and wake flow patterns from the impeller also do not agglomerate until 40% downstream of the throat. Additionally, the critical impact of the unsteady flow development on the time-averaged flow-field is explained.

Velocity spikes in separated flows

1966 ◽  
Vol 25 (1) ◽  
pp. 43-50 ◽  
Author(s):  
F. B. Hanson ◽  
S. H. Kozak ◽  
P. D. Richardson
Keyword(s):  
Large Scale ◽  
Separated Flow ◽  
Circular Cylinders ◽  
Hot Wire ◽  
Separated Shear Layer ◽  
Von Karman ◽  
Air Stream ◽  
Close Proximity ◽  
Karman Street ◽  
Von Kármán

In a recent study related to transition in the wake flows behind circular cylinders held transversely to an air stream, Bloor (1964) has reported the observation of velocity ‘spikes’ and attributed these to the close proximity to the hot wire of vortex centres on the opposite side of the von Kármán vortex street. Further observations of spikes are reported here, and the characteristics of their distribution indicate that other explanations of their form must be found. Some idealized flows are considered, and it is concluded that observations of spikiness within the hot-wire output may be accountable in terms of large-scale distributions of vorticity within the flow convected past the wire, the distributions being reasonable representations of a separated flow. The observations also provide some evidence that small vortices of Strouhal frequency exist on the inside of the coherent separated shear layer, and this may assist in the understanding of the feed-back mechanism where by the von Kármán street establishes itself as a self-perpetuating phenomenon.

Pitfalls of Hot-Wire Measurements Due to Transverse Wire Vibration

2002 ◽  
Author(s):  
Chris S. Anderson ◽  
O¨zden F. Turan ◽  
S. Eren Semercigil
Keyword(s):  
Experimental Verification ◽  
Large Scale ◽  
Natural Frequencies ◽  
Diameter Ratio ◽  
Small Scale ◽  
Hot Wire ◽  
Spectral Measurements ◽  
Flow Measurements ◽  
Numerical Predictions ◽  
Wire Vibration

Following from numerical predictions and large scale experimental verification, flow measurements are presented to show the effect of transverse wire vibrations on spectral measurements. It has been shown previously that if the first and second natural frequencies of a probe wire are close, it is expected to have favorable dynamic characteristics in turbulent flow. This expectation is confirmed with flow measurements. Further, the traditional sensing length to diameter ratio is reexamined for small scale measurements.

Planar Doppler velocimetry in a large-scale facility

AIAA Journal ◽  
2000 ◽  
Vol 38 ◽  
pp. 1010-1024 ◽  
Author(s):  
A. D. Mosedale ◽  
G. S. Elliott ◽  
C. D. Carter ◽  
T. J. Beutner
Keyword(s):  
Large Scale ◽  
Doppler Velocimetry
Sign in / Sign up

Export Citation Format

Share Document