scholarly journals Controlled Excitation of a Cold Turbulent Swirling Free Jet

1988 ◽  
Vol 110 (2) ◽  
pp. 234-237 ◽  
Author(s):  
R. Taghavi ◽  
E. J. Rice ◽  
S. Farokhi
Keyword(s):  
Acoustic Waves ◽  
Plane Waves ◽  
Acoustic Excitation ◽  
Mean Velocity ◽  
Instability Waves ◽  
Free Jet ◽  
Swirling Jet ◽  
Axial Mass ◽  
Change In The Mean ◽  
The Mean

Experimental results from acoustic excitation of a cold free turbulent jet with and without swirl are presented. A flow with a swirl number of 0.35 (i.e., moderate swirl) is excited internally by plane acoustic waves at a constant sound pressure level and at various frequencies. It is observed that the cold swirling jet is excitable by plane waves, and that the instability waves grow about 50 percent less in peak r.m.s. amplitude, and saturate further upstream compared to corresponding waves in a jet without swirl having the same axial mass flux. The preferred Strouhal number based on the mass-averaged axial velocity and nozzle exit diameter for both swirling and nonswirling flows is 0.4. So far no change in the mean velocity components of the swirling jet is observed as a result of excitation.

scholarly journals Dual plane PIV investigation of acoustically excited jets in a swirl nozzle

2015 ◽  
Vol 2 (5) ◽  
pp. 1407-1424
Author(s):  
G. S. Regunath ◽  
W. B. Zimmerman ◽  
J. M. Rees
Keyword(s):  
Energy Dissipation ◽  
Large Scale ◽  
Acoustic Excitation ◽  
Helical Structures ◽  
Gradient Tensor ◽  
Mean Velocity ◽  
Dual Plane ◽  
Piv Technique ◽  
Swirling Jet ◽  
The Mean

Abstract. A novel dual-plane dye laser PIV technique used to analyze helicity and energy dissipation in an unexcited turbulent swirling jet of pressurized cold air has established that regions within the flow field of the jet exhibiting high helicity are correlated with regions of high turbulent kinetic energy dissipation. This PIV configuration provides estimates of all components of the velocity gradient tensor, facilitating calculation of the helicity from the vorticity components. Application of this novel dual-plane PIV technique is extended in this study to investigate helical structures in a turbulent swirling jet where the underlying shear flow is subjected to external acoustic sinusoidal forcing in a plane perpendicular to the central axis of the jet. It was found that acoustic excitation had a significant effect on the mean velocity profile parallel to the direction of the jet. The horizontal forcing resulted in the generation of vorticity that was skewed with a pitch that favored a distribution of angles around 90° with respect to the velocity vector. The distribution of the time-averaged helicity angle indicated organized helical activity, but such activity is not dominated by large-scale coherent structures of maximal helicity.

scholarly journals Dual-plane PIV investigation of acoustically excited jets in a swirl nozzle

2016 ◽  
Vol 23 (2) ◽  
pp. 83-89
Author(s):  
Gavita S. Regunath ◽  
William B. Zimmerman ◽  
Julia M. Rees
Keyword(s):  
Energy Dissipation ◽  
Large Scale ◽  
Acoustic Excitation ◽  
Helical Structures ◽  
Mean Velocity ◽  
Dual Plane ◽  
Piv Technique ◽  
Swirling Jet ◽  
Image Velocimetry ◽  
The Mean

Abstract. A novel dual-plane dye laser particle image velocimetry (PIV) technique used to analyze helicity and energy dissipation in an unexcited turbulent swirling jet of pressurized cold air has established that regions within the flow field of the jet exhibiting high helicity are correlated regions of high turbulent kinetic energy dissipation. This PIV configuration provides estimates of all components of the velocity gradient tensor, facilitating calculation of the helicity from the vorticity components. Application of this novel dual-plane PIV technique is extended in this study to investigate helical structures in a turbulent swirling jet where the underlying shear flow is subjected to external acoustic sinusoidal forcing in a plane perpendicular to the central axis of the jet. It was found that acoustic excitation had a significant effect on the mean velocity profile parallel to the direction of the jet. The horizontal forcing resulted in the generation of vorticity that was skewed with a pitch that favored a distribution of angles around 90° with respect to the velocity vector. The distribution of the time-averaged helicity angle indicated organized helical activity, but such activity is not dominated by large-scale coherent structures of maximal helicity.

The Swirling Turbulent Jet

1972 ◽  
Vol 94 (4) ◽  
pp. 739-747 ◽  
Author(s):  
B. D. Pratte ◽  
J. F. Keffer
Keyword(s):  
Experimental Investigation ◽  
Static Pressure ◽  
Decay Rates ◽  
Turbulent Jet ◽  
Entrainment Rate ◽  
Self Similarity ◽  
Free Jet ◽  
Swirling Jet ◽  
Self Similar ◽  
The Mean

An experimental investigation has been made of a swirling jet having a moderate ratio of swirling to axial momentum. Measurements showed that the flow achieved a self-similarity for the mean velocities rather quickly while the normal turbulent intensities reached a self-similar state after a longer period of jet development. Conservation arguments were used to predict streamwise decay rates for the mean quantities. The analysis showed that the maximum axial and swirling velocity components should vary asymptotically as (x − x0)−1 and (x − x0)−2, respectively. The experimental results confirmed this satisfactorily. The minimum static pressure was predicted to vary at a rate proportional to (x − x0)−4. Measurements indicated, however, that the relation was closer to (x − x0)−2. Better agreement with the data was achieved when the analytical expression was adjusted for the effect of the turbulence terms. The entrainment rate and angle of spread for the swirling jet were found to be nearly twice that of the non-swirling free jet.

scholarly journals AERODYNAMICS AND AEROACOUSTICS SURVEY FOR A LOW SPEED SUBSONIC JET OPERATING AT MACH 0.25

2014 ◽  
Vol 13 (2) ◽  
pp. 33
Author(s):  
A. R. Proença ◽  
O. De almeida ◽  
R. H. Self
Keyword(s):  
Pitot Tube ◽  
Hot Wire ◽  
Mean Velocity ◽  
Low Speed ◽  
Free Jet ◽  
Acoustic Signature ◽  
Total Noise ◽  
Subsonic Regime ◽  
The Mean

The purpose of this work is to study and characterize, in laboratory, the aerodynamics of a free jet operating at subsonic regime and identify its acoustic signature. This study aims to analyze the fundamental role of turbulent flow structures in the total noise produced at different Mach numbers. This work is focused at low speed subsonic jets operating at Mach number 0.25. The research is done by analyzing the data obtained in experiments using Pitot tube, hot-wire anemometer and acoustic measurements. This work also describes the experimental procedures for each step of analysis, as well as the characteristics of jet noise facility. The data from measurements with Pitot tube is used to study the mean velocity profiles. The average properties are also analyzed with anemometry system, likewise used to study the turbulent intensity of eleven axial lines, ranging from the center line to the edge of the nozzle (lipline). These results are compared with the literature and is verified the accuracy of hot-wire anemometers for turbulent intensities lower than 15%. A database with the sound pressure level as a function of frequency is constructed from experiments serving as data for further numerical analysis to solve this problem.

scholarly journals Linear Stability Analysis of Chevron Jet Profiles

2006 ◽  
Author(s):  
Kristjan Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Linear Stability ◽  
Growth Rates ◽  
Sound Generation ◽  
Mode Structure ◽  
Mean Velocity ◽  
Strong Suppression ◽  
Instability Waves ◽  
Round Jets ◽  
Chevron Nozzles ◽  
The Mean

We investigate the linear stability characteristics of the mean velocity profiles produced by chevron nozzles. We show that chevron instability waves can be decomposed into azimuthal modes analogously to those of round jets. This facilitates a direct comparison of growth rates and mode structure between different nozzles. We find that the three nozzles used in this study share a set of modes, referred to as primary modes. In addition, we find that there exist modes unique to the chevrons nozzles, termed secondary modes. While chevron jets possess a much larger number of unstable modes, the modes with lowest azimuthal structure show strong suppression of growth rates in two different chevron jets. Some preliminary implications on sound generation are discussed.

Computational Analysis of Various Factors on the Edgetone Mechanism Using High Order Schemes

2005 ◽  
Author(s):  
Taku Nonomura ◽  
Hiroko Muranaka ◽  
Kozo Fujii
Keyword(s):  
Acoustic Waves ◽  
Feedback Loop ◽  
Stokes Equations ◽  
Computational Study ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
Good Correspondence ◽  
The Past ◽  
The Mean ◽  
Jet Velocity

Flow fields of two dimensional jets impinging on the sharp edge are computationally simulated and the effect of various parameters on the edgetone that is created by the flow interaction is investigated. Compressible Navier-Stokes equations are used so that acoustic waves are captured accurately as a part of feedback-loop. For numerical accuracy, Pade type compact finite difference scheme are used. First parameter is the jet velocity. Computational result shows good qualitative agreement with the experiment. Edgetone frequencies obtained by the computation also show good correspondence with those of experimental study in the past. Second parameter is the nozzle lip thickness. Although not considered in the computational study in the past, the nozzle lip thickness influences to the results. Amplitude of acoustics of larger nozzle lip is greater than that of smaller ones. This effect may comes from the fact that acoustic wave as a part of feedback loop is emphasized by nozzle lip. Third parameter is the jet-profile. Four different jet-profiles with the same maximum velocity (from top-hat profile to parabolic profile) and four different jet-profiles with the same mean velocity are computed. The mean jet velocity appears to have strong influence on the stage. The results also indicated that the mean jet velocity and the jet-profile have influence on edgetone frequencies.

Experimental Study on Compound Swirl Jet

2003 ◽  
Author(s):  
Tsutomu Nozaki ◽  
Takashi Ochiai ◽  
Tomonari Kai
Keyword(s):  
Experimental Study ◽  
Flow Visualization ◽  
Flow Rate ◽  
Rate Ratio ◽  
Flow Rate Ratio ◽  
Mean Velocity ◽  
Fundamental Study ◽  
Free Jet ◽  
The Mean ◽  
Two Jets

This paper concerns the fundamental study on the push-pull type ventilator, especially applied to the smoking table. In order to achieve more effective cleaning of the dirty air, a compound swirl jet, which consists of a round free jet having thick rim and a coaxial annular swirl jet was proposed by the authors. It was found that the compound flow is very useful for the push flow of the push-pull type ventilator selecting the suitable flow rate ratio of the annular swirl jet to the free jet. As a fundamental study on the compound swirl jet, the flow visualization was also carried out using the smoke method. At the same time, the mean velocity components were measured using the cobra Pitot tube. It was found from the results of these experiments that the unique flow structure by the interaction of two jets is created in the compound swirl jet choosing the adequate flow rate ratio, which is suitable for the push flow of the push-pull type ventilator.

The flow of liquid in a stream from the standard turbine impeller

1979 ◽  
Vol 44 (3) ◽  
pp. 700-710 ◽  
Author(s):  
Ivan Fořt ◽  
Hans-Otto Möckel ◽  
Jan Drbohlav ◽  
Miroslav Hrach
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Momentum Flux ◽  
Relative Size ◽  
Mean Velocity ◽  
Axial Profile ◽  
The Mean ◽  
Hot Film ◽  
Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

scholarly journals The mean velocity of posterior cerebral artery and basilar artery in Parkinson's disease with sleep disorders

2021 ◽  
Vol 4 ◽  
pp. 100207
Author(s):  
Muhammad Iqbal Basri ◽  
Ida Farida ◽  
Yudy Goysal ◽  
Jumraini Tammasse ◽  
Muhammad Akbar
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Sleep Disorders ◽  
Cerebral Artery ◽  
Basilar Artery ◽  
Posterior Cerebral Artery ◽  
Mean Velocity ◽  
The Mean
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