Compressibility Effects in Turbulent Subsonic Jets

2003 ◽  
Author(s):  
Zhexuan Wang ◽  
Yiannis Andreopoulos
Keyword(s):  
Mach Number ◽  
Pressure Fluctuations ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Jet Flows ◽  
Mean Velocity ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Mach Numbers ◽  
Response Pressure

The behavior of compressible turbulent jets issuing in still air in the absence of shock waves has been investigated at three different subsonic Mach numbers, 0.3, 0.6 and 0.9. Helium, nitrogen and krypton gases were used to generate the jet flows and investigate the density effects on the structure of turbulence. Particle Image Velocimetry and high-frequency response pressure transducers were used to obtain velocity, Mach number inside the flow field. The decay of the Mach number at the centerline of the axisymmetric jets increases with increasing the initial Mach number at the exit of the flow for all jets. The decay of mean velocity at the centerline of the jets is also higher at higher exit Mach numbers. However, the velocity non-dimensionalized by the exit velocity seems to decrease faster at low exit Mach numbers suggesting a reduced mixing with increasing the exit flow Mach numbers. Helium jets were found to have the largest spreading rate among the three different gas jets used in the present investigation, while krypton had the lowest spreading rate. Total pressure fluctuations appear to decrease with increasing exit flow Mach numbers. Unusually high turbulence intensities were measured in helium jets issuing in still air.

Measurements in subsonic and supersonic free jets using a laser velocimeter

1979 ◽  
Vol 93 (1) ◽  
pp. 1-27 ◽  
Author(s):  
Jark C. Lau ◽  
Philip J. Morris ◽  
Michael J. Fisher
Keyword(s):  
Mach Number ◽  
Error Function ◽  
Mixing Layer ◽  
Spreading Rate ◽  
Mean Velocity ◽  
Potential Core ◽  
Free Jets ◽  
Centre Line ◽  
Mach Numbers ◽  
Two Parameters

Velocity measurements in a 51 mm diameter turbulent jet are presented. The measurement programme is conducted in two parts. The first part is devoted to the validation of laser velocimeter (LV) data. This consists of comparative measurements with the LV and a hot-wire anemometer. The second part consists of a survey of the jet flow field at Mach 0·28, 0·90, and 1·37 under ambient temperature conditions. Radial and centre-line distributions of the axial and radial, mean and fluctuating velocities are obtained. The distributions indicate a decrease in the spreading rate of the mixing layer with increasing Mach number and a corresponding lengthening of the potential core. The results further indicate that these two parameters vary with the square of the jet Mach number. Radial distributions collapse when plotted in terms of ση*, where σ = 10.7/(1 - 0.273 MJ2) and η* = (r − r0·5)/x. This is true for distributions in planes located as far downstream as two potential core lengths. The collapsed data of mean velocity can be approximated by a Görtler error function profile: \[ U/U_J = 0.5[1-{\rm erf}(\sigma\eta^{*})]. \] Centre-line distributions at various Mach numbers also collapse if plotted in terms of x/xc, xc being the potential core length. A general equation for the collapsed data of mean velocity is given by: U/UJ = 1 - exp{1.35/(1 - x/xc)}, for the range of Mach numbers 0·3-1·4, where xc = 4.2 + 1.1 MJ2.

Influence of Flow Coefficient, Stagger Angle, and Tip Clearance on Tip Vortex in Axial Compressors

2006 ◽  
Vol 128 (6) ◽  
pp. 1274-1280 ◽  
Author(s):  
Yong Sang Yoon ◽  
Seung Jin Song ◽  
Hyoun-Woo Shin
Keyword(s):  
Pressure Fluctuations ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Time Resolved ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Response Pressure ◽  
Casing Pressure ◽  
Stagger Angle

Experiments have been performed on the low speed research compressor (LSRC) at General Electric Aircraft Engines to investigate the effects of flow coefficient, stagger angle, and tip clearance on tip vortex. Time resolved casing pressure distributions over the third stage rotor have been acquired with high-frequency-response pressure transducers. Also, tip vortex strength and trajectory have been estimated from the casing pressure fluctuations which have been obtained simultaneously from various axial locations. As flow coefficient decreases, tip vortex gets strengthened and migrates upstream. The stagger angle increase weakens the tip vortex and moves it downstream slightly because the blade loading is decreased. However, tip leakage vortex is influenced mainly by tip clearance, and there exists a “critical” tip clearance which determines the type of tip vortex trajectory (“straight” or “kinked”). As predicted by others, tip vortex gets strengthened with increasing tip clearance. However, unlike the predictions, the tip vortex trajectory moves upstream with increasing tip clearance. Furthermore, with tip clearance above a “critical” value, the tip vortex trajectory is no longer straight but shows a kink in the passage.

The Effect of the Operating Point on the Pressure Fluctuations at the Blade Passage Frequency in the Volute of a Centrifugal Pump

2002 ◽  
Vol 124 (3) ◽  
pp. 784-790 ◽  
Author(s):  
Jorge L. Parrondo-Gayo ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Joaquı´n Ferna´ndez-Francos
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Strong Increase ◽  
Flow Rates ◽  
Blade Passage ◽  
Pressure Transducers ◽  
Leading Role ◽  
Dynamic Forces ◽  
Response Pressure

An experimental investigation is presented which analyzes the unsteady pressure distribution existing in the volute of a conventional centrifugal pump with a nondimensional specific speed of 0.48, for flow-rates from 0% to 160% of the best-efficiency point. For that purpose, pressure signals were obtained at 36 different locations along the volute casing by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. Also, the experimental data obtained was used to adjust the parameters of a simple acoustic model for the volute of the pump. The results clearly show the leading role played by the tongue in the impeller-volute interaction and the strong increase in the magnitude of dynamic forces and dipole-like sound generation in off-design conditions.

Experimental Study of Interactions of Shock Wave With Free-Stream Turbulence

1994 ◽  
Vol 116 (4) ◽  
pp. 763-769 ◽  
Author(s):  
A. Honkan ◽  
C. B. Watkins ◽  
J. Andreopoulos
Keyword(s):  
Shock Wave ◽  
Free Stream ◽  
Length Scale ◽  
Pressure Transducers ◽  
Free Stream Turbulence ◽  
High Frequency Response ◽  
Reflected Shock ◽  
Response Pressure ◽  
Decaying Turbulence ◽  
Large Eddies

Phenomena related to turbulence interactions with shock waves have been studied in detail. The present investigation is focused on interactions of a normal shock wave with homogeneous/grid-generated turbulence. When a shock wave formed in a shock-tube is passed through a grid, the induced flow behind the shock has the features of a compressible flow with free-stream turbulence. The decaying turbulence is subjected to an interaction with the reflected shock traveling in the opposite direction. Data were sampled simultaneously from four channels of high frequency response pressure transducers and dual hot-wires probes. A cold-wire was used to provide instantaneous total temperature measurements while a single hot-wire provided instantaneous mass flux measurements. Amplification of velocity and temperature fluctuations and dissipative length scales has been found in all experiments. Velocity fluctuations of large eddies are amplified more than the fluctuations of small eddies. The dissipative length scale, however, of the large eddies is amplified less than the length scale of the small eddies.

scholarly journals Cavitation Inception in Spool Valves

1981 ◽  
Vol 103 (4) ◽  
pp. 564-575 ◽  
Author(s):  
C. Samuel Martin ◽  
H. Medlarz ◽  
D. C. Wiggert ◽  
C. Brennen
Keyword(s):  
Reynolds Number ◽  
Hydraulic Systems ◽  
Cavitation Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Annular Jet ◽  
Directional Control ◽  
Valve Opening ◽  
Response Pressure ◽  
Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

Compressibility effects in a turbulent annular mixing layer. Part 1. Turbulence and growth rate

2000 ◽  
Vol 421 ◽  
pp. 229-267 ◽  
Author(s):  
JONATHAN B. FREUND ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Growth Rate ◽  
Mach Number ◽  
Mixing Layer ◽  
Mixing Layers ◽  
Velocity Difference ◽  
Mean Velocity ◽  
The Mean ◽  
Mach Numbers ◽  
High Mach ◽  
Compressibility Effects

This work uses direct numerical simulations of time evolving annular mixing layers, which correspond to the early development of round jets, to study compressibility effects on turbulence in free shear flows. Nine cases were considered with convective Mach numbers ranging from Mc = 0.1 to 1.8 and turbulence Mach numbers reaching as high as Mt = 0.8.Growth rates of the simulated mixing layers are suppressed with increasing Mach number as observed experimentally. Also in accord with experiments, the mean velocity difference across the layer is found to be inadequate for scaling most turbulence statistics. An alternative scaling based on the mean velocity difference across a typical large eddy, whose dimension is determined by two-point spatial correlations, is proposed and validated. Analysis of the budget of the streamwise component of Reynolds stress shows how the new scaling is linked to the observed growth rate suppression. Dilatational contributions to the budget of turbulent kinetic energy are found to increase rapidly with Mach number, but remain small even at Mc = 1.8 despite the fact that shocklets are found at high Mach numbers. Flow visualizations show that at low Mach numbers the mixing region is dominated by large azimuthally correlated rollers whereas at high Mach numbers the flow is dominated by small streamwise oriented structures. An acoustic timescale limitation for supersonically deforming eddies is found to be consistent with the observations and scalings and is offered as a possible explanation for the decrease in transverse lengthscale.

Wall-vorticity flux dynamics in a two-dimensional turbulent boundary layer

1996 ◽  
Vol 309 ◽  
pp. 45-84 ◽  
Author(s):  
J. Andreopoulos ◽  
J. H. Agui
Keyword(s):  
Boundary Layer ◽  
Viscous Force ◽  
Flux Dynamics ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Wall Structures ◽  
Response Pressure ◽  
Vorticity Flux ◽  
Low Amplitude ◽  
Physical Phenomena

Four high-frequency-response pressure transducers with 10 viscous units resolution each have been used to obtain simultaneously the fluctuating pressure gradients at the wall of a zero-pressure-gradient boundary layer and then to compute the vorticity flux away from the wall. Since the viscous force on an element of incompressible fluid is determined by the local vorticity gradients, understanding of their dynamical characteristics is essential in identifying the turbulent structure. Extremely high and low amplitudes of both vorticity gradients have been observed which contribute significantly to their statistics although they have low probability of appearance. The r.m.s. of the vorticity flux when scaled with inner wall variables depends very strongly on the Reynolds number, indicating a breakdown of this type of scaling. The application of a small threshold to the data indicated two preferential directions of the vorticity flux vector. An attempt has been made to identify these high- and low-amplitude signals with physical phenomena associated with bursting-sweep processes. Vortical structures carrying bipolar vorticity are the dominant wall structures which are associated with the violent events characterized by large fluctuations of vorticity flux.

A Counter-Rotating Pair of Turbulent Jets

1973 ◽  
Vol 95 (2) ◽  
pp. 207-213 ◽  
Author(s):  
B. D. Pratte ◽  
J. F. Keffer
Keyword(s):  
Turbulent Jets ◽  
Spreading Rate ◽  
Mean Flow ◽  
Linear Superposition ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Free Jet ◽  
Intensity Measurements ◽  
Limited Application ◽  
Sectional Shape

A study has been made of a pair of swirling jets having opposite rotation. Mean flow and turbulent intensity measurements were obtained and characteristics of the spreading rate determined. The swirling component of mean velocity decayed rapidly in the streamwise direction and by about 35 dia, the flow had most of the characteristics of the single, free jet without swirl. A linear superposition was found to be of limited application near the jet source but gave reasonable results in the developed flow downstream. It was observed that the major and minor axes of the flow, defining the asymmetrical cross-sectional shape, underwent a reversal of position as the flow progressed downstream.

PIV measurements in a twin-jet STOVL fountain flow

2005 ◽  
Vol 109 (1100) ◽  
pp. 439-449 ◽  
Author(s):  
P. M. Cabrita ◽  
A. J. Saddington ◽  
K. Knowles
Keyword(s):  
Pressure Ratio ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Nozzle Pressure Ratio ◽  
Mean Velocity ◽  
Fountain Flow ◽  
Image Velocimetry ◽  
Nozzle Pressure

Abstract Mean velocity and first order turbulence measurements were obtained from a three-dimensional upwash fountain flow generated by the impingement of two compressible axisymmetric turbulent jets onto a normal plane. The jet impingement area and fountain formation regions were examined with data obtained through the use of particle image velocimetry. Seven configurations with different nozzle pressure ratios were considered to ascertain the influence of jet compressibility on the fountain development. Results indicate that the mixing of the fountain is dependent on the nozzle pressure ratio, leading to an increase in the fountain spreading rate with increase in nozzle pressure ratio.

scholarly journals Effect of Wind Tunnel Acoustic Modes on Linear Oscillating Cascade Aerodynamics

1993 ◽  
Author(s):  
Daniel H. Buffum ◽  
Sanford Fleeter
Keyword(s):  
Wind Tunnel ◽  
Unsteady Aerodynamics ◽  
Wave Mode ◽  
Influence Coefficient ◽  
Airfoil Surface ◽  
Pressure Transducers ◽  
Acoustic Modes ◽  
High Frequency Response ◽  
Response Pressure ◽  
Acoustic Treatment

The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes which have detrimental effects on the experimental results. Acoustic treatment is proposed to rectify this problem.

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