A directionally-sensitive laser anemometer for velocity measurements in highly turbulent flows

1975 ◽  
Vol 8 (8) ◽  
pp. 681-683 ◽  
Author(s):  
M K Denham ◽  
P Briard ◽  
M A Patrick
Keyword(s):  
Turbulent Flows ◽  
Velocity Measurements ◽  
Laser Anemometer ◽  
Highly Turbulent Flows

An Optical Instrument for Measuring Fluctuating Velocities in Highly Turbulent Flows

1978 ◽  
Vol 29 (2) ◽  
pp. 98-113 ◽  
Author(s):  
M. Gaster ◽  
J.F.M. Maybrey
Keyword(s):  
Turbulent Flows ◽  
Light Sources ◽  
Optical Instrument ◽  
Surface Reflection ◽  
Power Spectral ◽  
Optical Layout ◽  
Wide Range ◽  
Laser Anemometer ◽  
Sampling Zone ◽  
Highly Turbulent Flows

SummaryFlow measurement by optical devices of various types, particularly those involving laser light sources, have received considerable attention over the last few years. Different schemes employing a wide range of optical layouts have evolved and the resulting signals have been processed in a number of ingenious ways. We report new experimental work on an optical instrument that can be considered as the forerunner of the laser anemometer in the belief that in certain circumstances this particular optical layout offers some real advantages over the majority of laser anemometers. One important advantage of this system is the ease with which both the shape and size of the sampling zone can be independently controlled. Another is the ability to position the sampling region very close to a boundary without having to contend with the surface reflection difficulties that often prevent such measurements being made with laser optics. The instrument measures the velocities of small particles suspended in the fluid in much the same way as the laser anemometer. In unsteady flows this results in a series of velocity estimates generated at random time instants. These intermittent samples of the velocity are used to form power spectral density estimates by methods recently developed for the analysis of randomly sampled records (Gaster and Roberts, 1975 & 1976). This method of analysis could well be applied to the processing of the signals generated by laser anemometers operating in the burst counter mode.

A pulsed-wire technique for velocity measurements in highly turbulent flows

1971 ◽  
Vol 49 (4) ◽  
pp. 657-691 ◽  
Author(s):  
L. J. S. Bradbury ◽  
I. P. Castro
Keyword(s):  
Turbulent Flows ◽  
Time Of Flight ◽  
Measuring Technique ◽  
Velocity Measurements ◽  
Heated Air ◽  
Resistance Thermometers ◽  
Velocity Measuring ◽  
Highly Turbulent Flows ◽  
Flow Reversals

The velocity measuring technique described in this paper consists of measuring the time of flight of a tracer of heated air from an electrically pulsed wire to one of two sensor wires which are operated as resistance thermometers. These sensor wires are at right angles to the pulsed wire and are placed one on either side of the pulsed wire. The instrument may be used in highly turbulent flows including regions in which flow reversals occur. The paper discusses the theoretical behaviour of the probe and the results of some calibration experiments.

scholarly journals Laser Anemometry Techniques for Turbine Applications

1987 ◽  
Author(s):  
Mark P. Wernet ◽  
Lawrence G. Oberle
Keyword(s):  
Turbulent Flows ◽  
Time Of Flight ◽  
Nasa Lewis Research ◽  
Acceptance Angle ◽  
Flight System ◽  
Laser Anemometry ◽  
Laser Anemometer ◽  
Highly Turbulent Flows ◽  
Anemometer System ◽  
Comparison Measurements

Laser anemometry offers a nonintrusive means for obtaining flow field information. Our current research efforts at NASA Lewis Research Center are focused on instrumenting a warm turbine facility with a laser anemometer system. In an effort to determine the laser anemometer system best qualified for the warm turbine environment, we compared the performance of a conventional laser fringe anemometer and a two spot time-of-flight system with a new, modified time-of-flight system, called a Four Spot laser anemometer. The comparison measurements were made in highly turbulent flows near walls. The Four Spot anemometer uses elliptical spots to increase the flow acceptance angle to be comparable to that of a Laser Fringe Anemometer. Also, the Four Spot uses an optical code that vastly simplifies the pulse detection processor. The results of the comparison measurements will exemplify which laser anemometer system is best suited to the hostile environment typically encountered in warm rotating turbomachinery.

Lattice Boltzmann for Turbulence Modeling

2018 ◽  
Author(s):  
Sauro Succi
Keyword(s):  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
Turbulence Modeling ◽  
Real Life ◽  
Practical Interest ◽  
Reynolds Numbers ◽  
Full Resolution ◽  
To Come ◽  
Highly Turbulent Flows ◽  
Main Ideas

This chapter introduces the main ideas behind the application of LBE methods to the problem of turbulence modeling, namely the simulation of flows which contain scales of motion too small to be resolved on present-day and foreseeable future computers. Many real-life flows of practical interest exhibit Reynolds numbers far too high to be directly simulated in full resolution on present-day computers and arguably for many years to come. This raises the challenge of predicting the behavior of highly turbulent flows without directly simulating all scales of motion which take part to turbulence dynamics, but only those that fall within the computer resolution at hand.

scholarly journals WAVELET ANALYSIS CONSIDERATIONS FOR EXPERIMENTAL NONSTATIONARY FLOW PHENOMENA

2016 ◽  
Vol 15 (1) ◽  
pp. 67
Author(s):  
M. L. S. Indrusiak ◽  
A. J. Kozakevicius ◽  
S. V. Möller
Keyword(s):  
Turbulent Flows ◽  
Wavelet Transforms ◽  
Fourier Spectrum ◽  
Transient Flow ◽  
Wavelet Packet ◽  
Discrete Wavelet ◽  
Velocity Measurements ◽  
Discrete Wavelet Packet Transform ◽  
Flow Phenomena ◽  
The Fourier Transform

In this work, wavelet transforms are the analysis tools for studying transient and discontinuous phenomena associated to turbulent flows. The application in quest results from velocity measurements with hot wire anemometry in the transient wake considering a circular cylinder in an aerodynamic channel. Continuous and discrete wavelet transforms are applied and compared with the corresponding results given by the Fourier transform. For the continuous wavelet transform, the Morlet function was adopted as transform basis, and for the discrete case, the Daubechies orthonormal wavelet with 20 null moments. Results using the discrete wavelet packet transform are also presented and compared. A wake past a cylinder was analytically simulated and compared with the actual one, both in transient flow. The ability of the wavelet transforms in the analysis of unsteady phenomena and the potential of the wavelet approach as a complementary tool to the Fourier spectrum for the analysis of stationary phenomena is presented and discussed.

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