• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.784-788
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• 2004

A visualization study of shock formation of the supersonic jet nozzle using a Shadowgraph Method (SM) was carried out to investigate the effect of the longitudinal variation of coaxial pipe end tip position inside the supersonic nozzle. The experiment was performed for the Mach number range from 1.1 to 1.2 at nozzle exit. The well known shock cell structure was shown with the pipe end located deep inside the nozzle for the studied Mach number. With the pipe end approaches nozzle exit, it was found that the shock cell structure disappeared and turned into complex formation. In order to understand the mechanism of the shock structural change, computational simulation was carried out using the Navier-Stokes solver, FLUENT. Topological sketch was added with an aid of the visualization and the numerical simulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.6
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• pp.751-757
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• 2001

An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.

• 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.

• Journal of the Korean Society of Visualization
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• v.18 no.1
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• pp.50-58
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• 2020

This paper presents flow characteristics of a sweeping jet issued by a feedback-free fluidic oscillator. Overall flow characteristics of feedback-free sweeping jet (FFSJ) were analyzed using flow visualization. The feedback-free sweeping jet has a sinusoidal external flow pattern. The oscillating frequency of the FFSJ is three times higher than that of a conventional sweeping jet at the same Reynolds number. Flow structure and turbulence characteristics were investigated using time-resolved particle image velocimetry (TR-PIV). In instantaneous velocity fields, the flow did not stay at ends but changed the direction continuously in contrast to the conventional sweeping jet. Velocity distributions at each plane which were extracted from mean velocity field has Gaussian distribution, which is similar with a circular jet. The sweep angles were constant as 45° at all Reynolds numbers in the high flow rate regime.

• Korean Journal of Hydrosciences
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• v.6
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• pp.1-11
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• 1995

A plunge pool is often employed as an energy-dissipating device at the end of a spillway or a pipe culvert. A jet from spillways or pipes frequently generates a scour hole which threaten the stability of the hydraulic structure. Existing scour prediction formulas of plunge pool of spillways or pipe culverts give a wide range of scour depths, and it is, therefore, difficult to accurately predict those scour depths. In this study, a new experimental method and new sour prediction formulas under submerged circular jet for large bed materials with shallow tailwater depths were developed. A major variable, which was not used in previous scour prediction equations, was the ratio of jet size to bed material size. In this study, jet momentum acting on a bed particle and jet diffustion theory were employed to derive scour prediction formulas. Four theoretical formulas were suggested for the two regions of jet diffusion, i.e., the region of flow establishment and the region of established flow. The semi-theoretically developed scour prediction formulas showed close agreement with laboratory experiments performed on movable bed made of large spherical particles.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.134-143
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• 2001

Viscous solutions of supersonic jet impinging on a flat plate normal to the flow are simulated using three-dimensional Navier-Stokes solver. The jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. In the present study, the nozzle contour and the pressure ratio are held fixed, while the jet impinging distance is varied to illuminate the characteristics of the jet plume with the distance. As the plate is placed close to the nozzle at 3D high, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. Here D is the nozzle exit diameter. The amplitude of wall pressure fluctuations subsides as the distance increases, but the maximum pressure level at the plate is achieved when the distance is about 4D high. The frequency of the wall pressure is estimated at 6.0 kHz, 9.3 kHz, and 10.0 kHz as the impinging distance varies from 3D, 4D, to 6D, respectively.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.39-44
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• 2005

The numerical investigation of the interaction between the underexpanded supersonic jet and the perpendicular plate is carried out using the TVD numerical method. The wave structure in the flowfield and the pressure and temperature distributions on the plate surface are obtained by the numerical analysis. Especially, the influence of self-induced flow oscillation caused by the impinging jet and the characteristic of impinging jet are shown. From the result of the numerical analysis, it is concluded that the pressure and the temperature fluctuations on the plate surface strongly depends on the pressure ratio in the flowfield and the position of plate.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.225-228
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• 2002

Supersonic jet impingement on a flat plate has been investigated to show the flow physics for different jet heights and to demonstrate the adequacy of the characteristics-based flux-difference Wavier-Stokes code Current study also compares the steady-state solutions obtained with variable CFL number for different grid spacing with the time-accurate unsteady solutions using the inner iterations, displaying a good agreement between the two sets of numerical solutions. The unsteady nature of wall fluctuations due to bouncing of the plate shock is also uncovered for high pressure ratios. The methodology is then applied to a complex vertical launcher system where the jet plume hits the bottom wail, deflects into the plenum and eventually exits through the vertical uptake. Flow structures within vertical launcher system are captured and solutions are partially verified against the flight test data. Present jet impingement study thus shows the usefulness of CFD in designing a complex structure and predicting flow behavior within such a system.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.356-361
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• 2011

The flow characteristics of synthetic jet depending on rectangular and circular jet exit configuration are investigated using numerical computation with cross flow. In rectangular slot, synthetic jet generates the strong vortex, however, supply fewer momentum and effectiveness of flow control is reduced along flow direction. In circular slot, regular vortex is fanned from slot center to end and developed in flow direction. It affects the wider region than rectangular slot. The distribution of wall shear stress is considered in order to indicate the effectiveness of flow control device for flow separation delay. As a result, circular slot is a more suitable candidate for delaying flow separation.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.28-34
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• 2002

A computational study of supersonic flow around lateral jet controlled missile has been performed. For this study, three dimensional Navier-Stokes code(AADL3D) has been developed. Spalart-Allmaras one equation turbulence model has been implemented on the AADL3D code for relatively rapid computational time. For the validation of developed code, AADL3D, pressure distributions on an ogive-cylinder body has been compared with experimental data. Also, the shock structure of sonic jet on the flat plate in the supersonic flow field has been compared with experimental flow visualization result to see the analysis capability of freestream-jet interaction case. A case study has been performed through comparing the normal force coefficient and the moment coefficient of missile body for several jet flow conditions. Current results will be used to the optimum design of a lateral jet controlled missile.