• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.34-41
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• 1997

The objective of this study is to investigate experimentally the frequency characteristics of the hole tones generated by a circular jet of low speed impinging on a plate with a round hole. The experimental results about the sound spectrum and the time wave of the hole tone are presented and discussed in relation with the hole type, the jet velocity and the distance of the nozzle-to-plate with a round hole. From the sound spectrum and time wave measurements, it is found that the hole tone is generated not only by an interaction of convected vortices with a round hole but also by a series of vortex shedding from jets passing through a hole. The hole tones generated by a feedback mechanism consist of many frequency stages and also have a hysteresis phenomenon like an edge tone. But the hole tones generated by a series of vortex shedding have nothing with the stage characteristics. The frequencies of hole tones are influenced by the jet velocity, the distance of the nozzle-to-plate with a round hole and the hole type.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.798-803
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• 2003

The objective of the present study is to investigate the changes in the acoustic source characteristics and far-field noise propagation in an incompressible round jet at Re=10000 for single-frequency excitations using large eddy simulation and Lighthill acoustic analogy. We apply excitations at a frequency corresponding to the jet-column mode ($St_{D}=0.85$) or maximum growth rate in the shear layer ( $St_{\theta}=0.017$ ). The acoustic source derived from the Lighthill acoustic analogy is the second spatial derivative of the Reynolds stresses. In the case of $St_{D}=0.85$, vortex ring and large scale structures are dominant sources, whereas in the case of $St_{\theta}=0.017$, the main sources are located at an upstream position along the shear layer than in the uncontrolled case. Also, the far-field noise propagates along the axial direction due to excitation.

• Water Engineering Research
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• v.2 no.2
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• pp.89-101
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• 2001

The theoretical treatments on jets, in which the flow is issuing into a stagnant medium, have been based on Prandtl's mixing theory. In this study, using Prandtl's mixing length hypothesis, a theoretical relationship for the velocity profile of a single round jet is derived. Furthermore, Gaussian expression is used to approximate the theoretical relationship, in which the Gaussian coefficient is assumed to be decreasing exponentially as the flow goes far from the orifice. Two data sets for a single round jet performed by tow different techniques of measurement are used to verify the suggested relationships. The theoretical and Gaussian distribution give close results in spite of the difference in approach. The observed mean velocity distributions are in good agreements with the suggested theoretical and Gaussian distributions.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.49.2-49.2
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• 2005

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.49-55
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• 2013

The goal of the research is to evaluate the open source code of OpenFOAM for the use of nuclear plant flow simulation objectively. Of the various incompressible flow solvers, simpleFoam, pimpelFoam are then tested under three validated cases (backward facing step, flow over circular cylinder and turbulent round jet flow). For the evaluation of steady state incompressible laminar flow simulation, low reynolds number of backward facing step flow was solved by simpleFoam. The resultant of the reattached lengths turned out to be similar with the other experimental and simulation results. For transient flow simulation, flow over circular cylinder and turbulent round jet flow were solved by pimpleFoam. The simulation accuracy was evaluated by comparing the resultant flow patterns with the description of the characteristics of the flow over the circular cylinder. The quantitative accuracy was evaluated for no more than 85% by comparing it to the decaying constants of the turbulent round jet velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1472-1479
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• 2003

An attempt to reduce supersonic jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10 mm. Two micro-nozzles with an inside diameter of 1 mm each are installed on the exit plane at an angle of 45 relative to the main jet axis. Far-field noise was measured at 40 diameters off the jet axis. The angle between a microphone and the jet axis is 30 or 90$^{\circ}$. For an injection rate of 4-6% of the main jet, screech tones were completely suppressed by the microjets. The reduction in the overall sound pressure levels were 2.4 and 2.7 dB for 90 and 30 measuring directions, respectively. However, the enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or deformed large scale vortical structures by the microjets.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.1-13
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• 2004

A scanning stereo-PIV system was developed to measure the three-dimensional distribution of three-component velocity in a turbulent round jet. A laser light beam produced by a high repetition rate YLF pulse laser was expanded vertically by a cylindrical lens to form a laser light sheet. The light sheet is scanned in a direction normal to the sheet by a flat mirror mounted on an optical scanner, which is controlled by a programmable scanner controller. Two high-speed mega-pixel resolution C-MOS cameras captured the particle images illuminated by the light sheet, and stereoscopic PIV method was adopted to acquire the 3D-3C-velocity distribution of turbulent round jet in an octagonal tank filled with water. The jet Reynolds number was set at Re=1000 and the streamwise location of the measurement was fixed at approximately x = 40D. Time evolution of three-dimensional vortical structure, which is identified by vorticity, is visualized. It revealed that the existence of a group of hairpin-like vortex structures was quite evident around the rim of the shear layer of the jet. Turbulence statistics shows good agreement with the previous data, and divergence of a filtered (unfiltered) velocity vector field was $7\%\;(22\%)$ of root-me an-squared vorticity value.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1566-1574
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• 1992

Local heat transfer characteristics for a round air jet impinging normally on a heated flat plate were experimentally investigated. The problem parameters investigated were jet Reynolds number, Re=4000,10000, and 20000, and nozzle-to-plate spacing(L/D) of 2,6, and 10. The temperature variations on the flat uniform heat flux surface were mapped using a thermo-sensitive liquid crytal sheet. The isochromatic images corresponding to the characteristic temperature of liquid crystal were analyzed with the help of a digital image processing system. The local Nusselt number, Nu decreased rapidly in the impingement region and exhibited a similar profiles in the wall jet region independent of the nozzle-to-plate spacing L/D. In the case of large Reynolds number, heat transfer rate (Nu) was proportional to 0.5 power of the Reynolds number. For L/D=2, a secondary peak in the heat transfer rate was seen in the region of X/D=1.5~3 due to the transition from laminar to turbulent boundary layer.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.747-750
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• 2002

An attempt to reduce supersonic Jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10mm. Two micro-nozzles with an inside diameter of 1mm each are installed on the exit plane with an off-axis angle of $45^{\circ}$. Far-field noise was measured at a location 40 diameters off the jet axis. The angles between a microphone and the jet axis are $45^{\circ}\;and\;90^{\circ}$. For an injection rate less than $1{\%}$ of the main jet, screech tones were completely suppressed by the microjets. The reduction in the ovelall sound pressure levels were $2.4\;and\;2.7\;dB\;for\;90^{\circ}\;and\;45^{\circ}$ directions, respectively. The enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or broken large scale vortical structures by the microjets.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.8
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• pp.1211-1224
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• 2004

Two round jets. impinged and pulsed. were measured with high-resolution 3D-PTV technique. The measurement system consists of three CCD cameras, Ar-ion laser, an image grabber and a host computer. Two fitness functions were introduced in a genetic algorithm in order to enhance the correspondences of the particles. One was based on a concept of the continuum theory and the other one was based on a minimum distance error. The velocity profiles of the impinged jet obtained by the constructed 3D-PTV system were compared with those of LDV measurements made in this study. The head vortex of the jet was visualized by LIF and was reconstructed by the constructed high-resolution 3D-PTV system for comparisons.