• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.54-60
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• 2017

In order to identify the characteristics of the flame transfer function gain, cold-flow transfer function was introduced, which is the part of the combustion instability research. Nitrogen and carbon dioxide was used to obtain the cold-flow transfer function and input/output variables was measured by hot wire anemometry. Density and fluid flow rate affect the cold-flow transfer function gain and peak frequency. In addition, acoustic resonance frequency affects the peak frequency of gain in the fuel feeding line.

• Journal of ILASS-Korea
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• v.20 no.3
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• pp.135-140
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• 2015

Flame transfer function is used to determine the relationship between flow fluctuations and heat release perturbations in a lean premixed gas turbine combustor. The characteristics of flame transfer function are known to depend greatly on flame geometries in addition to other various flow conditions. However, it is not easy to experimentally measure the flame transfer function under various actual combustor operating conditions in terms of time and cost. The current research tries to model the flame transfer function using CFD(Computational Fluid Dynamics). From the results, it is shown that the calculated steady flame geometry can be exactly captured with consideration of the wall heat transfer and radiations. Also, unsteady analysis results show the close characteristics of the flame transfer function to the measured one in both gain and phase.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.1172-1177
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• 1993

Dynamic characteristics of a hydraulic power supply are studied theoretically and computationally. The transfer function between the supply pressure and the load flow is derived considering relief valve dynamics, accumulator dynamics, and flow line dynamics. Frequency responses and time responses are obtained in many conditions using the transfer function and nonlinear mathematical model respectively.

• 대한공업교육학회지
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• v.34 no.1
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• pp.238-251
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• 2009

The noise itself that affects the sensor array is defined as the noise which happens in the place where the system is installed and the circumference noise which comes from the ocean. The array structure for detecting acoustic signal in the underwater effected turbulent layer flow noise. In this paper to design the conformal array spectral density function was introduced and several cases of flow induced noise which affect transfer function were simulated. Modified Corcos wall pressure model was used as turbulent boundary layer flow noise. The effect of noise has been reduced as integrated sum of transfer function has been reduced by decreasing elastomer thickness and density when kx is in low wave number area. Also the characteristics of transfer function by Corcos wall pressure displayed the product of frequency density function. This simulation results can be applied to the conformal array design in unmmaned underwater vehicle in the near future.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.53-54
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• 2012

In an IGCC plant, one of the most important issues on fuel flexibility in the lean premixed combustor is combustion instabilities. They are characterized by large amplitude pressure oscillations which are caused by unsteady heat release from the flames. The relationship between the unsteady heat release and flow oscillation can be qualitatively and quantitatively explained by flame transfer function. This paper introduces combustion instability modeling methods based on the flame transfer function approach.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2384-2389
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• 2007

The 2nd order response surface method (RSM) has been carried out to get optimum thermal design for enhanced heat transfer on square channel with bleed holes. The RSM was used as an optimization technique with Reynolds-averaged navier-stokes equation. Turbulence model for heat transfer analysis used RNG k-epsilon model. The wall function used enhanced wall function. Numerical local heat transfer coefficients were similar to the experimental tendency. Two design variables such as attack angle of rib (${\alpha}$), rib pitch-to-rib height ratio (p/e) were chosen. Operation condition considered bleeding ratio per bleed hole ($BR_{hole}$). A response surface were constructed by the design variables and operation condition. As a result, adjusted $R^2$ was more than 0.9. Optimization results of various objective function were similar to heat transfer in channel with and without bleed flow. But friction factor was lower than channel without bleed flow.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.7
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• pp.667-673
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• 2000

In order to understand the laminar flow heat transfer enhancement by the swirl flow, the effects of heat transfer in a circular pipe with a twisted tape insert were investigated experimentally. In the present study, the uniform heat flux condition was considered. The laminar heat transfer correlations were developed using the least-square-fit from the surface temperature distribution of an electrically-heated pipe and flow property data. Average Nusselt number correlations with the twisted tape insert were expressed as a function of swirl parameter, Reynolds number and Prandtl number. In the case of the twisted ratio y = 6.05, the mean Nusselt number increased approximately 500% and the friction factor increased approximately 300%, compared to the case of the empty pipe, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.10
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• pp.2586-2594
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• 1995

Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.8-19
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• 2016

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ${\omega}RSM$ turbulence model. Additionally, the RNG $k-{\varepsilon}$, SSG RSM, and $SST_+{\gamma}-Re_{\theta}$ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ${\omega}RSM$ results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The $SST_+{\gamma}-Re_{\theta}$ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1351-1359
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• 2003

This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.