• Proceedings of the KSME Conference
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• 2001.11b
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• pp.462-467
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• 2001

The present study addresses a computational work of the weak shock wave propagatings inside a silencer system of automobile exhaust pipe. Four different types of the silencer systems and the initial shock wave Mach number $M_s$ of $1.01\sim1.30$ are applied to investigate their effects on the noise reduction and the flow field in a silencer system. The results obtained from the present computational work are compared with the experimental results. The second order total variation diminishing (TVD) scheme is employed to solve the two dimensional, compressible, unsteady, Euler equations. The present computational results predict the experimental results with a quite good accuracy. Of the four silencer systems applied, the most desirable silencer system to reduce the peak pressure at the exit of the exhaust pipe is discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.19-22
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• 2003

Ejector-diffuser system is one of fluid machinery which can entrain the fluid in low pressure part and transport it to the higher pressure part. The conventional ejector-diffuser system has been pointed out that its overall efficiency is quite low compared with other fluid machinery since it is derived by only the pure shear stresses. In the present study, 4, 6, and 8 lobed petal nozzles with a design Mach number of 1.7 are adopted as a primary nozzle to improve the performance, and are compared with a conventional circular nozzle.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.67-71
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• 2003

The propagation characteristics of the impulse wave discharged from the exit of a perforated pipe is investigated through a simple shock tube facility. The pressure histories and directivities of the impulse wave propagating outside from the exit of pipe with several different configurations are analyzed for the range of the incident weak shock wave Mach number between 1.02 and 1.2. In the shock tube experiments, the impulse wave are visualized by a Schlieren optical system for the purpose of understanding its propagation characteristics. The experimental results show that for the near sound field the impulse noise strongly propagates toward to the pipe axis, but for the far sound field the impulse noise uniformly propagates toward to the omnidirections, indicating that the directivity pattern is almost same regardless of the pipe type. Especially, it is shown that the perforated pipe has a little performance to reduce the impulse noise only for the near sound field

• Advances in aircraft and spacecraft science
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• v.2 no.4
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• pp.367-389
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• 2015

Simple solutions are obtained for the fuel required by internal combustion engine airplanes on trajectories with a constant rate of climb or descent. Three modes of flight are considered: constant speed, constant Mach number and constant angle of attack. Starting from the exact solutions of the equations of motion for the modes of motion considered, approximate solutions are obtained that are much easier to compute while still being quite precise. Simpler formulas are derived for the weight of fuel, speed, altitude, horizontal distance, time to climb, and power required. These formulas represent a new important contribution since they are fundamental for the analysis of aircraft dynamics and thus have direct applications for the analysis of aircraft performances and mission planning.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.437-448
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• 2017

The problem of flow through the vent is formulated as an unsteady, nonlinear, ordinary differential equation and solved using Runge-Kutta method to obtain pressure inside payload faring. An inverse problem for prediction of the discharge coefficient is presented employing measured internal pressure of the payload fairing during the ascent phase of a satellite launch vehicle. A controlled random search method is used to estimate the discharge coefficient from the measured transient pressure history during the ascent period of the launch vehicle. The algorithm predicts the discharge coefficient stepwise with function of Mach number. The estimated values of the discharge coefficients are in good agreement with differential pressure measured during the flight of typical satellite launch vehicle.

• Solar Energy
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• v.18 no.2
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• pp.115-121
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• 1998

In this study a channel cavity flow was performed. The channel has small size in the upper cavity region. At the gap is supplied by driven flow for Reynolds number. The experimental study was carried out in a channel cavity with square heat surface by visualization equipment with Mach-Zehnder interferometer and laser apparatus. Heat source was uniform heat flux($0.4W/cm^2,\;0.8W/cm^2,\;1.2W/cm^2$). When the bottom wall is heated, the tendency of natural convection flows are vigorous increasing heat flux.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.75.2-75.2
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• 2010

We have studied the statistical properties of turbulence in molecular clouds identified in the Boston University - Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS). Toward this end, the probability density function (PDF) and velocity distribution were measured for about 50 molecular clouds. We found there exists a good correlation between the PDF width and the velocity dispersion for these molecular clouds. In order to investigate how general properties of astrophysical turbulence depends on the plasma parameters such as magnetic field strength and sonic Mach number, we performed three-dimensional MHD simulations. We then examined if the observed characteristics of interstellar turbulence are consistent with theoretical results from MHD simulations.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.85-94
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• 1999

Transient aerodynamic response of an airfoil to a moving plane-flap is numerically investigated using two-dimensional Euler equations with conservative Chimera grid method. A body moving relative to a stationary grid is treated by an overset grid bounded by a 'dynamic domain-dividing line' the concept of which is developed in this study. A conservative Chimera grid method with a dynamic domain-dividing line technique is applied and validated by solving the flowfield around circular cylinder moving supersonic speed. The unsteady and transient characteristics of the flow solver is also examined by computations of a oscillating airfoil and a ramp pitching airfoil respectively. The transient aerodynamic behavior of an airfoil with a moving plane-flap is analyzed for various flow conditions such as deflecting rate of flap and free stream Mach number.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.71-76
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• 1999

The base flow regions of a three-body sounding rocket containing multiple exhaust plumes were numerically investigated in three dimensions for a free stream Mach number of 2.7 at flight altitude 18.5 km. The flowfields were calculated using the full compressible Navier-Stokes equations with an one-equation turbulence model of Baldwin-Earth. The present calculations were executed based upon a chemically frozen, single perfect gas model assumption. Due to the symmetry of the three-body rocket of each single nozzle, only one fourth of the computational domain was considered for the analysis. The results indicate that a babe heating effect is not considerable due to the small expansion of the plumes. In the base, however, a low speed recirculating flow dominates the region.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.17-22
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• 1999

Convergence characteristics and efficiency of three implicit approximate factorization schemes(ADI, DDADI and MAF) are examined using 2-Dimensional compressible upwind Navier-Stokes code. Second-order CSCM(Conservative Supra Characteristic Method) upwind flux difference splitting method with Fromm scheme is used for the right-hand side residual evaluation, while generally first-order upwind differencing is used for the implicit operator on the left-hand side. Convergence studies are performed using an example of the flow past a NACA0012 airfoil at steady transonic flow condition, i. e. Mach number 0.8 at $1.25^{\circ}$ angle of attack. The results were compared with other computational results in order to validate the current numerical analysis. The results from the implicit AF algorithms were compared well in low surface with the other computational results; however, not well in upper surface. It might be due to lack of the grid around the shock position. Because the algorithm minimizes the errors of the approximate decomposition, the improved convergence rate with MAF were observed.