• The Journal of the Acoustical Society of Korea
• /
• v.15 no.6
• /
• pp.52-58
• /
• 1996

Using the acoustic resonances and oscillatory pulsations considered as the branch of wave technologies, the concept of the acoustic resonance diffusers for waste water treatment which maximize the oxygen transfer efficiency in gas-liquid two phase medium have been proposed, and studies for the principles and performance tests were accomplished. Besides, the design concepts for the low pressure Helmholtz resonator, cylinder and annular type reflection resonator and combined type resonance system have been implemented. The acoustic resonance energy which can speed up the mass transfer process increase the oxygen transfer efficiency, and periodic pulsations generated from the instability of air jet from nozzle make very small air bubbles. Then, the annular type jet resonator(AJR) applying these two principles successfully was evalulated as the most promising device and also the efficiency showing $20{\sim}30%$ better than conventional diffusers has been verified experimentally.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.6
• /
• pp.1-10
• /
• 2018

An experimental study was performed for the behavior of the burner flame which results from burning of the liquid hydrocarbon fuel atomized by an ultrasonic transducer. Configurations of the flame and combustion-field were caught by both high-speed camera and thermo-graphic camera, and those images were analyzed in detail through a image post-processing. As a result, the combustion-field grew and reaction-temperature rose due to the strengthening of combustion reaction with the increasing flow-rate of carrier-gas. In addition, a phenomenon of flame flickering was discussed through the comparative analysis of the variational behavior between the visible flame and IR (Infrared) flame-field. Also, the flickering frequency of the flame was confirmed through FFT (Fast Fourier Transform) analysis employing the flame area.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.4
• /
• pp.293-301
• /
• 2017

A Sub-kWe small-scale experimental test loop was manufactured to investigate characteristics of the supercritical carbon dioxide power cycle. A high-speed turbo-generator was also designed and manufactured. The designed rotational speed of this turbo-generator was 200,000 rpm. Because of the low expansion ratio through the turbine and low mass flowrate, the rotational speed of the turbo-generator was high. Therefore, it was difficult to select the rotating parts and design the turbine wheel, axial force balance and rotor dynamics in the lab-scale experimental test loop. Using only one channel of the nozzle, the partial admission method was adapted to reduce the rotational speed of the rotor. This was the world's first approach to the supercritical carbon dioxide turbo-generator. A cold-run test using nitrogen gas under an atmospheric condition was conducted to observe the effect of the partial admission nozzle on the rotor dynamics. The vibration level of the rotor was obtained using a gap sensor, and the results showed that the effect of the partial admission nozzle on the rotor dynamics was allowable.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.20 no.1
• /
• pp.43-49
• /
• 2016

An experimental study was performed to investigate the combustion characteristics of the liquid hydrocarbon fuel atomized by an ultrasonic oscillator. Configuration of the flame was caught by the DSLR camera, and images were analyzed in detail through a post-processing. Temperature of the flame zone was measured using thermocouple. It is resulted that the flame area is proportional to the mass flow rate of carrier gas as well as the voltage applied to the ultrasonic oscillator. Temperature of the flame zone is measured and analyzed according to variation in the operating condition of the burner, too.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.20 no.11
• /
• pp.1025-1032
• /
• 2010

Gas turbine compressor blades used in a combined cycle power plant are possibly damaged and fractured during their operation. There are two possible causes of the failure of compressor blades; one is a defect of material quality which can be detected through some microscopic inspections for the fracture section, the other is high cycle fatigue problem caused by vibration and can be diagnosed by carrying out dynamic characteristics analysis for the blades. In this paper, in order to determine the cause of the failure of compressor blades in a combined cycle power plant, examination of the fracture section and the propagation mechanism of the crack via stress analysis are performed. Dynamic characteristics analysis via FRF estimation is also performed to identify the cause of failure.

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

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.9
• /
• pp.1229-1237
• /
• 1998

Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.11a
• /
• pp.200-203
• /
• 2000

The application of the ultrasonic nozzle has been extended because it is possible atomization of liquid material. In this study, the characteristics of the ultrasonic nozzle and ceramic oscillator were investigated. The oscillator for the ultrasonic nozzle were made piezoelectric ceramic of Pb[($Sb_{1/2}$ $Nb_{1/2}$)$_{0.035}$-($Mn_{1/3}$$Nb_{2/3}$)$_{0.065}$-($Zr_{0.49}$$Ti_{0.51}$)$_{0.90}$]$O_3$. The electromechanical coupling factor($k_p$) and mechanical quality factor(Qm) showed the values of 0.555, 1, 214 respectively when the Zr/Ti ratio was 49/51. Moreover, this oscillator will have the temperature stability because it's curie temperature is 322[$^{\circ}C$]. The driving current of ultrasonic nozzle showed the value of 80[mA] when the driving time was lO[min.]. Also, The surface temperature of ceramic oscillator showed 80[$^{\circ}C$] at driving time lO[min.] We knew that the ultrasonic nozzle had stabile driving above 10[min.].

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.3
• /
• pp.31-40
• /
• 2020

The structure and dynamics of multiple shock waves are studied numerically using a finite volume solver for a model with nozzle exit Mach number of 1.75. At first, the shock variation based on images were analyzed using a Matlab program then later to the wall static pressure variation. The amplitude and frequency variation for multiple shock waves are analyzed. The cross-correlation between the shock location suggests that the first and the second shocks are well correlated while the other shocks show a phase lag in the oscillation characteristics. The rms values of pressure fluctuations are maximum at the shock locations while the other parts in the flow exhibit a lower value os standard deviation.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.3
• /
• pp.309-319
• /
• 2011

We experimentally investigated lifted propane jet flames diluted with nitrogen to obtain flame-stability maps based on heat-loss-induced self-excitation. We found that heat-loss-induced self-excitations are caused by conductive heat loss from premixed flame branches to trailing diffusion flames as well as soot radiation. The conductive-heat-loss-induced self-excitation at frequencies less than 0.1 Hz is explained well by a suggested mechanism, whereas the oscillation of the soot region induces a self-excitation of lift-off height of the order of 0.1 Hz. The suggested mechanism is also verified from additive experiments in a room at constant temperature and humidity. The heat-loss-induced self-excitation is explained by the Strouhal numbers as a function of the relevant parameters.