• Journal of the Korean Society of Combustion
• /
• v.9 no.4
• /
• pp.1-8
• /
• 2004

Zone conditional formulation for the Reynolds average reaction progress variable is used to derive an asymptotic expression for turbulent burning velocity. New DNS runs are performed for validation in a statistically one dimensional steady state configuration. Parametric study is performed with respect to turbulent intensity, integral length scale, density ratio and laminar flame speed. Results show good agreement between DNS results and the asymptotic expression in terms of measured maximum flame surface density and estimated turbulent diffusivity in unburned gas.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.7
• /
• pp.2337-2346
• /
• 1996

One of the most useful method for increasing combustion loading of premixed flame is to strengthen the turbulent intensity of unburned mixture. It produces an important information to a design of efficient combustion equipment that analysing microstructure of strong turbulence premixed flame. The flame structure and characteristics are depend on the turbulence of unburned mixture. Therefore, to strengthen the turbulent intensity of unburned mixture make flame scale small and accomplish efficient combustion. We measured the velocity of local flame front movements, local eddy radius and local reaction zone thickness quantitatively with increasing turbulent intensity of unburned mixture. We researched the microstructure of flame using ion currents that react sensitively in the reaction zone. Consequently, the velocity of local flame front movements is depend on the velocity of unburned mixture and local eddy scale is to be small with increasing turbulent intensity. But there is no change in local reaction zone thickness with turbulence.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.8
• /
• pp.1191-1200
• /
• 2002

The measurements of velocity vectors are made in the near wake(X/d=5.0) of a circular cylinder with serrated fins. Velocity of fluid which flow through fins decreases as increasing fin height and freestream velocity and decreasing fin pitch. Therefore the velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. The discontinuity of the streamwise velocity gradient is observed near the fin edge and causes significant changes in V-component velocity distribution in the near wake. This change attributes to the differences in Strouhal number and entraintment flow behavior. Increased turbulent intensity around a circular cylinder due to the serrated fins and entrainment flow are important factors for the recovery of velocity defect. The widths of velocity and turbulent intensity distribution of fin tubes are wider than those of a circular cylinder. The normalized velocity and turbulent intensity distributions with a hydraulic diameter which is proposed in this paper are in closer agreement with those of a circular cylinder.

• 한국연소학회:학술대회논문집
• /
• 2004.11a
• /
• pp.62-69
• /
• 2004

Zone conditional formulations for the Reynolds average reaction progress variable are used to derive an asymptotic expression for turbulent burning velocity. New DNS runs are performed for validation in a statistically one dimensional steady state configuration. Parametric study is performed with respect to turbulent intensity, integral length scale, density ratio and laminar flame speed. Results show good agreement between DNS results and the asymptotic expression in terms of measured maximum flame surface density and estimated turbulent diffusivity in unburned gas.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2001.05a
• /
• pp.28-33
• /
• 2001

Animation understanding and time-resolved analysis of the wake characteristic of 2-D sharp plane flows were executed by applying the multi-vision PIV to a sharp plane(three angle of attacks : $15^{\circ}, \; 30^{\circ}, \; 45^{\circ}$) submerged within a circulating water channel($Re = 2{\times}10^4$). The macroscopic shedding patterns were discussed in terms of instantaneous velocity, vorticity, velocity profile, kinetic energy, turbulent intensity, frequency analysis. Particularly, the time-averaged distribution of turbulent intensity in each experimental cases revealed separate island-like small regions magnitude of turbulent intensity was always strengthened.

• 한국연소학회:학술대회논문집
• /
• 2006.04a
• /
• pp.128-134
• /
• 2006

A characterization of turbulent reacting flows has proved difficult owing to the complex interaction between turbulence, mixing, and combustion chemistry. There are many types of time scales in turbulent flame which can determine flame structure. This counter jet type premixed burner produces high intensity turbulence. The goal is to gain better insights into the flame structures at high turbulence. 6 propane/air flames gave been studied with high velocity fluctuation in bundle type nozzle and in one hole type nozzle. By measuring velocity fluctuation, turbulent intensity and integral length scale are obtained. And sets of OH LIF images were processed to see flame structure of the mean flame curvatures and flame lengths for comparison with turbulence intensity and turbulent length scales. The results show that the decrease in nozzle size generates smaller flow eddy and mean curvatures of the flame fronts, and a decrease in Damkohler number estimated from flow time scale measurement.

• Journal of the Korean Society of Visualization
• /
• v.3 no.1
• /
• pp.78-89
• /
• 2005

An experimental study was carried out to investigate the effect of local ultrasonic forcing on a turbulent boundary layer. Stereoscopic particle image velocimetry (SPIV) was used to probe the characteristics of the flow. A ultrasonic forcing system was made by adhering six ultrasonic transducers to the local flat plate. Cavitation which generates uncountable minute air-bubbles having fast wall normal velocity occurs when ultrasonic was projected into water. The SPIV results showed that the wall normal mean velocity is increased in a boundary layer dramatically and the streamwise mean velocity is reduced. The skin friction coefficient (C$_{f}$) decreases 60$\%$and gradually recovers at the downstream. The ultrasonic forcing reduces wall-region streamwise turbulent intensity, however, streamwise turbulent intensity is increased away from the wall. Wall-normal turbulent intensity is almost the same near the wall but it increases away from the wall. In the vicinity of the wall, Reynold shear stress, sweep strength and production of turbulent kinetic energy were decreased. This suggests that the streamwise vortical structures are lifted by ultrasonic forcing and then skin friction is reduced.

• 한국연소학회:학술대회논문집
• /
• 2007.05a
• /
• pp.7-12
• /
• 2007

To reveal the newly found liftoff height behavior of hydrogen jet, we have experimentally studied the stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition. The objectives of the present research are to report the phenomenon of a liftoff height decreasing as increasing fuel velocity, to analyse the flame structure and behavior of the lifted jet, and to explain the mechanisms of flame stability in hydrogen turbulent non-premixed jet flames. The velocity of hydrogen was varied from 100 to 300m/s and a coaxial air velocity was fixed at 16m/s with a coflow air less than 0.1m/s. For the simultaneous measurement of velocity field and reaction zone. PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. As results, it has been found that the stabilization of lifted hydrogen diffusion flames is related with a turbulent intensity, which means that combustion occurs where the local flow velocity is valanced with the turbulent flame propagation velocity.

• Proceedings of the KSME Conference
• /
• 2000.11b
• /
• pp.267-271
• /
• 2000

The local heat transfer rate of an axisymmetric submerged air jet impinging on normal to a heated flat plate was investigated experimentally with varying solidity of mesh screen. The mean velocity and turbulent Intensity profiles of streamwise velocity component were measured using a hot-wire anemometry. The temperature distribution on the heated flat surface was measured with thermocouples. The screen installed in front of the nozzle exit(behind of 35mm) modify the jet flow structure and local heat transfer characteristics. For higher solidity screen, turbulence intensity at core lesion is high and increases the local heat transfer rate at nozzle-to-plate spacings(L/D<6). For larger nozzle-to-plate spacings(L/D>6), however, the turbulent Intensities of all screens tested in this study approach to an asymptotic curve, but the small mean velocity at the core region reduces the local heat transfer rate for high solidity screens.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.2 no.3
• /
• pp.188-198
• /
• 1990

Turbulent characteristics of turbulent pulsating flows were studied experimentally in a square duct. Velocity waveforms, velocity profiles, and turbulent intensity of turbulent pulsating flow were investigated by using a hot-wire anemometer with data acquisition and a processing system in a square duct with a ratio of 1 ($40mm{\times}40mm$) to 4,000mm long. Turbulent components were shown to be larger in decelerating than in accelerating regions and also larger for a large phase of velocity and U'rms distribution of turbulent flow. The effect of velocity amplitude ratio does not exist for specified time [${\theta}(z^{\prime})$], amplitude ratio (${\mid}U^{\prime}_{rms.os.1}{\mid}/{\mid}U_{m.os.1}{\mid}$), and phase difference (${\Delta}U^{\prime}_{rms.os.1}-{\Delta}U_{m.os.1}$) in either turbulent oscillating or cross-sectional mean velocity components. The effect of dimensionless angular frequency for specified time [${\theta}(z^{\prime})$] can be disregarded because the dimensionless angular frequency does not affect the specified time. The velocity distributions of turbulent pulsating flows for various time-averaged Reynolds numbers are in approximate agreement with the velocity distributions for equivalent Reynolds numbers and 1/7th power law of steady flow.