Experimental Study of a Jet-Driven Helmholtz Oscillator

This paper describes an experimental study of a Helmholtz resonator driven by a round jet passing through it. This device, dubbed the jet-driven Helmholtz oscillator (JDHO), is a rigid chamber with two round openings located coaxially in two opposite walls, through which a jet is allowed to pass across the chamber. At certain jet velocities, jet instabilities couple with the Helmholtz resonance to produce very powerful chamber-pressure oscillations at a frequency slightly higher than the chamber Helmholtz frequency. The amplitude of these pressure oscillations may reach values of up to 5.6 times the jet dynamic pressure. Simultaneously, the exiting flow pulsates at the same frequency with an amplitude of up to 60 percent of the exit jet velocity, and a loud sound is emitted. The thrust of the present study was twofold: to determine the optimum range of geometrical parameters producing the maximum magnitudes, and to identify the mechanisms underlying the oscillator operation.

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Experimental Study on Dynamic Combustion Characteristics in Swirl-Stabilized Combustors

Energies ◽

10.3390/en14061609 ◽

2021 ◽

Vol 14 (6) ◽

pp. 1609

Author(s):

Donghyun Hwang ◽

Kyubok Ahn

Keyword(s):

Experimental Study ◽

Heat Release ◽

Dynamic Pressure ◽

Combustion Instability ◽

Flame Structure ◽

Pressure Sensors ◽

Necessary Condition ◽

Rayleigh Criterion ◽

Pressure Oscillations ◽

Geometric Conditions

An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.

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Experimental study of impinging turbulent round jet flow on a square cylinder laid on a flat plate

Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer ◽

10.1615/ichmt.2006.turbulheatmasstransf.890 ◽

2006 ◽

Author(s):

N. S. Kim ◽

Andre Giovannini ◽

G. Harran

Keyword(s):

Experimental Study ◽

Flat Plate ◽

Jet Flow ◽

Square Cylinder ◽

Round Jet

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The Effect of Longitudinal Core Flow on Trailing Vortex Stability

Volume 7: Fluids Engineering Systems and Technologies ◽

10.1115/imece2014-38522 ◽

2014 ◽

Author(s):

Amir Allaf-Akbari ◽

A. Gordon L. Holloway ◽

Joseph Hall

Keyword(s):

Experimental Study ◽

Velocity Field ◽

Kinetic Energy ◽

Vortex Core ◽

Vortex Generator ◽

Core Flow ◽

Vortex Stability ◽

Vorticity Distribution ◽

Air Jet ◽

Jet Velocities

The current experimental study investigates the effect of longitudinal core flow on the formation and structure of a trailing vortex. The vortex is generated using four airfoils connected to a central hub through which a jet flow is added to the vortex core. Time averaged vorticity, circumferential velocity, and turbulent kinetic energy are studied. The statistics of vortex wandering are identified and corrections applied to the vorticity distribution. The vortex generator used in this study was built on the basis of the design described by Beninati et al. [1]. It uses four NACA0012 airfoils connected to a central hub. The wings orientation can be adjusted such that each contributes to a strong trailing vortex on the center of the test section. The vortex generator also had the capability to deliver an air jet directed longitudinally through a hole in the hub at the joint of the airfoils. Tests were done without the jet and with the air jet at jet velocities of 10 and 20 m/s. Planar PIV was used to measure the velocity field in the vicinity of the vortex core. The measurements were taken at 3 chords behind the vortex generator.

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Rotating Stall in Centrifugal Compressor Vaneless Diffuser: Experimental Analysis of Geometrical Parameters Influence on Phenomenon Evolution

International Journal of Rotating Machinery ◽

10.1155/s1023621x04000430 ◽

2004 ◽

Vol 10 (6) ◽

pp. 433-442 ◽

Cited By ~ 22

Author(s):

Giovanni Ferrara ◽

Lorenzo Ferrari ◽

Leonardo Baldassarre

Keyword(s):

Centrifugal Compressor ◽

Dynamic Pressure ◽

Pressure Sensors ◽

Experimental Tests ◽

Fast Response ◽

Rotating Stall ◽

Geometrical Parameters ◽

Vaneless Diffuser ◽

Response Dynamic ◽

Frequency Domains

The rotating stall is a key problem for achieving a good working range of a centrifugal compressor and a detailed understanding of the phenomenon is very important to anticipate and avoid it. Many experimental tests have been planned by the authors to investigate the influence on stall behavior of different geometrical configurations. A stage with a backward channel upstream, a 2-D impeller with a vaneless diffuser and a constant cross-section volute downstream, constitute the basic configuration. Several diffuser types with different widths, pinch shapes, and diffusion ratios were tested. The stage was instrumented with many fast response dynamic pressure sensors so as to characterize inception and evolution of the rotating stall. This kind of analysis was carried out both in time and in frequency domains. The methodology used and the results on phenomenon evolution will be presented and discussed in this article.

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Experimental Study of the Jet Engine Exhaust Flow Field of Aircraft and Blast Fences

PROMET - Traffic&Transportation ◽

10.7307/ptt.v27i2.1545 ◽

2015 ◽

Vol 27 (2) ◽

pp. 181-190 ◽

Cited By ~ 2

Author(s):

Haifu Wang ◽

Liangcai Cai ◽

Xiaolei Chong ◽

Hao Geng

Keyword(s):

Experimental Study ◽

Flow Field ◽

Wind Velocity ◽

Maximum Rate ◽

Dynamic Pressure ◽

Jet Flow ◽

Engine Exhaust ◽

Jet Engine ◽

Jet Nozzle

A combined blast fence is introduced in this paper to improve the solid blast fences and louvered ones. Experiments of the jet engine exhaust flow (hereinafter jet flow for short) field and tests of three kinds of blast fences in two positions were carried out. The results show that the pressure and temperature at the centre of the jet flow decrease gradually as the flow moves farther away from the nozzle. The pressure falls fast with the maximum rate of 41.7%. The dynamic pressure 150 m away from the nozzle could reach 58.8 Pa, with a corresponding wind velocity of 10 m/s. The temperature affected range of 40°C is 113.5×20 m. The combined blast fence not only reduces the pressure of the flow in front of it but also solves the problems that the turbulence is too strong behind the solid blast fences and the pressure is too high behind the louvered blast fences. And the pressure behind combined blast fence is less than 10 Pa. The height of the fence is related to the distance from the jet nozzle. The nearer the fence is to the nozzle, the higher it is. When it is farther from the nozzle, its height can be lowered.

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An Experimental Study on the Influence of Structural Damping on Internal Fluid Pressure During a Transient Flow

Journal of Pressure Vessel Technology ◽

10.1115/1.2928627 ◽

1990 ◽

Vol 112 (3) ◽

pp. 284-290 ◽

Cited By ~ 6

Author(s):

D. D. Budny ◽

F. J. Hatfield ◽

D. C. Wiggert

Keyword(s):

Experimental Study ◽

Transient Flow ◽

Traditional Approach ◽

Dynamic Pressure ◽

Fluid Pressure ◽

Piping System ◽

Internal Dynamic ◽

Structural Damping ◽

Pipe System ◽

Internal Fluid

The traditional approach to designing a piping system subject to internal dynamic pressure is to restrain the piping as much as possible, and the approximation made in the analysis is to assume no contribution of structural energy dissipation. To determine the validity of this concept and approximation, an experimental study of a piping system was performed to measure the influence of structural damping. A pipe system was designed with a loop that could be turned so that its natural frequency would match that of the contained liquid. It was discovered that a properly sized damper on the piping loop greatly accelerates the decay of the fluid pressure transient. The damper absorbs some energy from the piping, reducing the resulting rebound fluid pressure. When the loop is subjected to forced steady-state vibration, there is a fluid pressure response. The amplitude of that pressure can be reduced by installing an external damper: the stiffer the damper the more effective it is in reducing dynamic pressure.

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Experimental Study on Pressure Fluctuations in the Boundary Layer of an Axisymmetric Body

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.66-68.1488 ◽

2011 ◽

Vol 66-68 ◽

pp. 1488-1493

Author(s):

Hong Xiao ◽

Chao Gao ◽

Zhen Kun Ma

Keyword(s):

Boundary Layer ◽

Experimental Study ◽

Mach Number ◽

Dynamic Pressure ◽

Pressure Fluctuations ◽

Axisymmetric Body ◽

Pressure Measurements ◽

Fluctuating Pressure ◽

Frequency Domains ◽

Dynamic Pressure Measurements

The characteristics of the fluctuating pressure in the boundary layer of an axisymmetric body have been investigated experimentally using dynamic pressure measurements and Schlieren photograghs. Data were acquired at subsonic and super-sonic Mach numbers. The angles of attack ranged from 0° to 5°. Pressure signals were measured simultaneously in several positions along the model and were analyzed both in the time and frequency domains. The Mach number shows the relevant influence on . Furthermore, the pressure fluctuations’ level decreases with the increasing of Mach number except M=1.15. And it is shown that, the location along the axis of the model and the angles of attack have small effect on pressure fluctuations.

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