• Wind and Structures
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• v.5 no.1
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• pp.49-60
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• 2002

This paper describes a simple method for evaluating the design wind loads for the structural frames of circular flat roofs with long spans. The dynamic response of several roof models were numerically analyzed in the time domain as well as in the frequency domain by using wind pressure data obtained from a wind tunnel experiment. The instantaneous displacement and bending moment of the roof were computed, and the maximum load effects were evaluated. The results indicate that the wind-induced oscillation of the roof is generally dominated by the first mode and the gust effect factor approach can be applied to the evaluation of the maximum load effects. That is, the design wind load can be represented by the time-averaged wind pressure multiplied by the gust effect factor for the first mode. Based on the experimental results for the first modal force, an empirical formula for the gust effect factor is provided as a function of the geometric and structural parameters of the roof and the turbulence intensity of the approach flow. The equivalent design pressure coefficients, which reproduce the maximum load effects, are also discussed. A simplified model of the pressure coefficient distribution is presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1371-1378
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• 1999

Flow through turbomachinery has a very complex structure and Is Intrinsically unsteady. In addition, trend to highly loaded turbomachinery makes the flow extremely complex due to the interaction between rotor and stator. In this study, flows through UTRC LSRR turbine are numerically analyzed using 2 dimensional Navier-Stokes equations. The convective terms of the governing equations are discretized using the Van-Leer's FVS(Flux vector splitting) with an upwind TVD scheme. The conventional central differencing is used to discretize the diffusion terms on the finite volume. The accurate unsteady motion is achieved by using a 2nd order accurate, 3-point Euler implicit scheme. The quasi-conservative zonal scheme is used for calculating the flow variables on the zonal interface between the rotor and stator. The axial gap between stator and rotor has been configured in two variations, 15% and 65% of average chord length. The analysis program is validated using experimental results and the effect of axial gap is examined. The numerical analysis results are presented by time averaged pressure coefficient and pressure magnitude coefficient and compared with experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.685-694
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• 2002

Effects of wake-passing orientation and frequency on the wake-induced boundary layer transition on a NACA0012 airfoil are investigated. The wakes are generated by rotating cylinders clockwise (CW) and counterclockwise (CCW) around the airfoil. Time- and phase-averaged streamwise mean velocities and turbulent fluctuations are measured with a single hot-wire probe. Wall skin frictions are estimated by the Computational Preston Tube Method (CPM). The pressure distribution on the airfoil is different according to the wake-passing orientation and frequency. Turbulent patches are generated in the laminar boundary layer due to the passing wake and the boundary layer becomes temporarily transitional. The transition process is significantly affected by the pressure gradient and the turbulent patches. For the receding wake, the turbulent patches propagate more rapidly than those for the approaching wake because adverse pressure gradient becomes larger. As the frequency increases, onset location of transition moles upstream and the boundary layer near the trailing edge becomes more transitional.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.619-629
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• 1998

An experimental work was conducted to investigate a feasibility of simultaneous measurement of gas-liquid two-phase flowrates with double orifice plates using air and water. The tests were carried out under the atmospheric pressure and at the ambient temperature using two different tube sizes. Qualities of an air-water flow in the present study have values less than 0.1 and thus the mixed flow showed bubbly, plug, slug flow regimes. The probability density function (PDF) and the power spectral density function (PSDF) of the instantaneous pressure drop traces for the flow regimes were obtained. It is found that some distinctive features exist in the distribution of these functions, depending upon the two-phase flow pattern. The time-averaged value of the instantaneous pressure drop increases with increasing gas and liquid flowrates, showing a single-valued function for the total mass flowrate and the quality. It is also found that the two-phase discharge coefficient exhibits a consistent trend for variation of dimensionless parameters such as the superficial velocity ratio and the gas Reynolds number. The results indicate that simultaneous measurement of two-phase flowrate may be possible based upon a statistical analysis of the instantaneous pressure drop curves monitored using double orifice plates.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.21-24
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• 2005

Numerical analysis were made for the unsteady flow fields of the rotor system of a Tilt-Rotor aircraft in cruise mode. The Reynolds-averaged thin-layer Wavier-Stokes equations were discretized by Roe's upwind differencing scheme and integrated in time by the LU-SGS algorithm. The computational domain of the rotor system was constructed by seven multi-block Chimera grids. Comparison of pressure coefficient on the surface of the main wing and blades were made for 3cases of advance ratio(0.325, 0.350, 0.375) and thrust and power coefficients for the rotor were compared with experimental data.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.2
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• pp.200-209
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• 1998

Experiments have been conducted to determine heat transfer characteristics for a two-dimen-sional turbulent wall attaching offset jet at different oblique angles to a flat surface. The local Nusselt number distributions were measured using liquid crystal as a temperature sensor. Wall static pressure coefficient profiles were measured at the Reynolds number Re 53200(based on the nozzle width, D) the offset ratio H/D from 2.5 to 10 and the oblique angle a from $0^{\circ}$, to $40^{\circ}$ It is observed that the maximum Nusselt number point occurs slightly upstream of time-averaged reattachment point for all oblique angles. The correlations between the maximum Nusselt number and Reynolds number offset ration and oblique angle are presented.

• Advances in aircraft and spacecraft science
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• v.7 no.4
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• pp.371-385
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• 2020

A forward-facing aerospike attached to a payload fairing of a satellite launch vehicle significantly alters its flowfield and decreases the aerodynamic drag in transonic and low supersonic speeds. The present payload fairing is an axisymmetric configuration and consists of a blunt-nosed body along with a conical section, payload shroud, boat tail and followed by a booster. The main purpose of the present numerical simulations is to evaluate flowfield and assess the performance of aerodynamic drag coefficient with and without aerospike attached to a payload fairing of a typical satellite launch vehicle in freestream Mach number range 0.8 ≤ M_∞ ≤ 3.0 and freestream Reynolds number range 33.35 × 10⁶/m ≤ Re_∞ ≤ 46.75 × 10⁶/m whichincludes the maximum aerodynamic drag and maximum dynamic conditions during ascent flight trajectory of the satellite launch vehicle. A numerical simulation has been carried out to solve time-dependent compressible turbulent axisymmetric Reynolds-averaged Navier-Stokes equations. The closure of the system of equations is achieved using the Baldwin-Lomax turbulence model. The aerodynamic drag reduction mechanism is analysed employing numerical results such as velocity vector plots, density and Mach contours in conjunction with the experimental flow visualization pictures. The variations of wall pressure coefficient over the payload fairing with and without aerospike are exhibiting different kind of flowfield characteristics in the transonic and low supersonic speeds. The numerically computed results are compared with schlieren pictures, oil flow patterns and measured wall pressure distributions and exhibit good agreement between them.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1649-1660
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• 1996

The flow around a circular cylinder was controlled by an acoustic excitation issued from a thin slit along the cylinder axis. The static pressure distributions around the cylinder wall and flow characteristics in the near wake have been measured. Experiments were performed under three cases of Reynolds number, 7.8 * 10$\^$4/, 2.3 * 10$\^$5/ and 3.8 * 10$\^$5/. The effects of excitation frequency, sound pressure level and the location of the slit were examined. Data indicate that the excitation frequency and the slit location are the key parameters for controlling the separated flow. At Re$\_$d/, = 7.8 * 10$\^$4/, the drag is reduced and the lift is generated to upward direction, however, at Re$\_$d/, =2.3 * 10$\^$5/ and 3.8 * 10$\_$5/, the drag is increased and lift is generated to downward direction inversely. It is thought that the lift switching phenomenon is due to the different separation point of upper surface and lower surface on circular cylinder with respect to the flow regime which depends on the Reynolds number. Vortex shedding frequencies are different at upper side and lower side. Time-averaged velocity field shows that mean velocity vector and the points of maximum intensities are inclined to downward direction at Re$\_$d/ = 7.8 * 10$\^$4/, but are inclined to upward direction at Re$\_$d/ = 2.3 * 10$\^$5/.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.567-576
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• 1999

An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.1
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• pp.93-103
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• 2008

This study was conducted to optimize a unidirectional flushing program in distribution pipes by analysis of water pressure, velocity, quality, and other parameters during flushing. As a result, correlation coefficient between flushed pipe length and the flushing duration was obtained $R^2=0.83$ and the equation $Y_{Time}=0.0571{\cdot}X_{Pipe\;length}+4.7648$ for 10 pipes. The averaged flushing velocity in the pipes, 1.1 m/s, was enough to remove loose deposits on the inner wall of the pipes. 3 of 92 water samples taken during flushing met the National Drinking Water Quality Standard for Fe and Mn, but not for Al. Turbidity less than 1 NTU is suggested for the appropriate criteria to finish flushing in pipes. The coefficient of determination ($R^2$) between turbidity and TSS was 0.95 and the equation was induced as $Y_{TSS}=1.2068{\cdot}X_{Turbidity}$. The amount of removed deposits could be estimated from the turbidity data of discharged water in field because turbidity and TSS in the discharged water is highly correlated.