• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.5
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• pp.668-676
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• 2003

The effect of nozzle height on heat transfer of a hot steel plate cooled by an impinging liquid jet is not well understood. Previous studies have been based on the dimensionless parameter z/d. To test the validity of this dimensionless parameter and to investigate gravitational effects on the jet, stagnation velocity of an impinging liquid jet were measured and the cooling experiments of a hot steel plate were conducted for z/d from 6.7 to 75, and an inverse heat conduction method is applied for the quantitative comparison. Also, the critical instability point of a liquid jet was examined over a range of flow rates. The experimental velocity data for the liquid jet were well correlated with the dimensionless number 1/F $r_{z}$$^2$based on distance. It was thought that the z/d parameter was not valid for heat transfer to an impinging liquid jet under gravitational forces. In the cooling experiments, heat transfer was independent of z when 1/F $r_{z}$$^2$< 0.187(z/d = 6.7). However, it was found that the heat transfer quantity for 1/F $r_{z}$$^2$=0.523(z/d = 70) is larger 11% than that in the region for 1/F $r_{z}$$^2$=0.187. The discrepancy between these results and previous research is likely due to the instability of liquid jet.uid jet.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.89.1-89.1
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• 2011

We have investigated a coronal jet near the limb on 2010 June 27 by Hinode/X-Ray Telescope (XRT), EUV Imaging Spectrograph (EIS), Solar Optical Telescope (SOT), SDO/Atmospheric Imaging Assembly (AIA), and STEREO. From EUV (AIA and EIS) and soft X-ray (XRT) images we identify the erupting jet feature in cool and hot temperatures. It is noted that there was a small loop eruption in Ca II images of the SOT before the jet eruption. Using high temporal and multi wavelength AIA images, we found that the hot jet preceded its associated cool jet. The jet also shows helical-like structures during the rising period. According to the spectroscopic analysis, the jet structure changes from blue shift to red one with time, implying the helical structure of the jet. The STEREO observation, which enables us to observe this jet on the disk, shows that there was a dim loop associated with the jet. Comparing the observations from the AIA and STEREO, the dim loop corresponds to the jet structure which implies the heated loop. Considering that the structure of its associated active region seen in STEREO is similar to that in AIA observed 5 days before, we compared the jet morphology on the limb with the magnetic fields extrapolated from a HMI vector magnetogram observed on the disk. Interestingly, the comparison shows that the open field corresponds to the jet which is seen as the dim loop in STEREO. Our observations (XRT, SDO, SOT, and STEREO) are well consistent with the numerical simulation of the emerging flux reconnection model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.323-327
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• 1991

An experiment was conducted to determine the local heat transfer from a supersonic hot jet impinging at 45.deg. to a plate surface. A semi-analytic method was used to determine the Nusselt number from experimental data. The results indicates that the location of the peak heat transfer is displaced from the geometric center of the axisymmetric jet and that the radial variation of the local heat transfer is steeper than that in the subsonic impinging jet. In the stagnation region, the heat transfer from the supersonic impinging jet is about 10 times larger than that from the subsonic one, while the heat transer away from the stagnation region is of the same magnitude as that of the in compressible turbulent radial wall jet.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.92-97
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• 2003

By using a centerbody injection, an effort to reduce shock assoicated noise is made in an underexpanded sonic nozzle with an exit diameter of 10mm. The centerbody or micro nozzle, aligned with the axis of the main jet has an o.d. of 2mm and i.d. of 1.5mm. When measured at 90$^{\circ}$ relative to the main jet the farfield noise spectra showed that the screech tones and broadband shock associated noise can be significantly reduced simply by varying the length of the centerbody and/or mass fraction of the microjet. The maximum reduction in overall sound pressure level (OASPL) was as much as 9 and 4 ㏈ at fully expanded jet Mach numbers Mi of 1.3 and 1.5, respectively, when the length of the centerbody was varied from 0 to 4 main nozzle diameters without blowing. With the aid of the blowing, the maximum reduction in OASPL increased to 12 and 7 ㏈ at M$\sub$j/=1.3 and 1.5, respectively. The impact pressure field in the main jet plume strongly suggested that the reduced periodic pressure distribution in the shear layers and/or centerline is responsible for the reduced screech and broadband shock associated noise. Therefore, the steady blowing by a micro centerbody is a promising technique for shock noise reduction in a supersonic jet.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.11 no.1
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• pp.41-55
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• 2003

A calibration jet system using separate blower is developed to calibrate a flow sensor effectively. Designed open circuit type mini calibration jet system, which has the dimension of $0.5m(W){\times}1.17m(H)$ is small compared with conventional calibration jet systems. The exit of nozzle has exchangeable contractions with a cross section area of $38.5cm^2$ , and a cross section area of $113.1cm^2$, respectively. The ranges of wind speed at exit of exchangeable nozzles are $7.5{\sim}42\;m/s$ and $1.8{\sim}16.5\;m/s$, respectively. The input power for the high pressure blower is 1.18kW. The turning vanes for corner was rolled flat plate parallel to the flow direction. The flow conditioning screen was located immediately downstream of the wide-angle diffuser. The honeycomb and two flow conditioning screens were located in the stagnation chamber. From the economical point of view and the simplicity of the calibration jet system set up and handling, it can be said that the developed calibration jet system is an effective calibration jet system. This system can also be used to calibrate the flow sensor with high resolution.

• 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.

• 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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.414-423
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• 1994

The planar laminar impingement jet with a confinement plate has been studied numerically. Discretzing the convection term with the QUICKER scheme, the full Navier-Stokes equations for fluid flow were solved using the well known SIMPLER algorithm. The flow characteristics with Reynolds number and jet exit velocity profile effects on it were considered for H=3, Re=200 - 2000. Results show that vortical flow forms in turn along the confinement and impingement plates as the Reynolds number increases and such a complicated flow pattern has never been reported prior. The jet exit velocity profile is shown to do an important role in determining the position of vortex flow and its size as well as in stagnation and wall jet flow region. Parabolic jet exit profile results in peak of skin friction 1.4-1.6 times greater than that of uniform profile. The channel height effects are also studied and shown to have an effect on flow pattern similar to that of Reynolds number. Also shown is that effects of the jet exit velocity profile becomes less significant over a certain channel height.

• Clean Technology
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• v.25 no.3
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• pp.238-244
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• 2019

In this study, the ignition characteristics of petroleum-based aviation fuel (Jet A-1), bio aviation fuel (Bio-6308), and blended aviation fuel (50:50, v:v) were analyzed in accordance with change of temperature and pressure. The ignition delay time of each aviation fuel was measured by combustion research unit (CRU) and the compositions of the fuels were analyzed by GC/MS and GC/FID for qualitative and quantitative results. From the results, it was confirmed that the ignition delay times of all aviation fuels were shortened with increasing temperature and pressure. In particular, the effect of temperature was larger than the effect of pressure. Also, the ignition delay time of Jet A-1 was the longest at all measurement conditions, and it was judged that this result is because of the structurally stable characteristics of the benzyl radical generated during the oxidation reaction of the aromatic compound (about 22.48%) in Jet A-1. Also, it was confirmed that Jet A-1 had no section where the degree of shortening of ignition delay time was decreased by increasing temperature, which was because the benzyl radical inhibits the response that can affect the negative temperature coefficient (NTC). The ignition characteristics of blended aviation fuel (50:50, v:v) showed a similar tendency to those of Jet A-1, rather than to those of Bio-6308, so that the blended aviation fuel (50:50, v:v) can be applied to the existing system without any change.

• Journal of The Korean Astronomical Society
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• v.47 no.4
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• pp.159-161
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• 2014

The jet production efficiency of radio galaxies can be quantified by comparison of their kinetic jet powers $P_{jet}$ and Bondi accretion powers $P_B$. These two parameters are known to be related linearly, with the jet power resulting from the Bondi power by multiplication with an efficiency factor of order 1%. Using a recently published (Nemmen & Tchekhovskoy 2014) high-quality sample of 27 radio galaxies, I construct a $P_B$ - $P_{jet}$ diagram that includes information on optical AGN types as far as available. This diagram indicates that the jet production efficiency is a function of AGN type: Seyfert 2 galaxies seem to be systematically (with a false alarm probability of $4.3{\times}10^{-4}$) less efficient, by about one order of magnitude, in powering jets than Seyfert 1 galaxies, LINERs, or the remaining radio galaxies. This suggests an evolutionary sequence from Sy 2s to Sy 1s and LINERs, controlled by an interplay of jets on the one hand and dust and gas in galactic nuclei on the other hand. When taking this effect into account, the $P_B$ - $P_{jet}$ relation is probably much tighter intrinsically than currently assumed.