• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.186-191
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• 2004

The reactive flowfield of the transverse injecting combustor has been studied using Euler-Lagrange method in order to develop an efficient solution procedure for the understanding of liquid spray combustion in the transverse injecting combustor which has been widely used in ramjets and turbojet afterburners. The unsteady two-dimensional gas-phase equations have been represented in Eulerian coordinates and the liquid-phase equations have been formulated in Lagrangian coordinates. The gas-phase equations based on the conservation of mass, momentum, and energy have been supplemented by combustion. The vaporization model takes into account the transient effects associated with the droplet heating and the liquid-phase internal circulation. The droplet trajectories have been determined by the integration of the Lagrangian equation in the flow field obtained from the separate calculation without considering the iterative effect between liquid and gas phases. The reported droplet trajectories had been found to deviate from the initial conical path toward the flow direction in the very end of its lifetime when the droplet size had become small due to evaporation. The integration scheme has been based on the TEACH algorithm for gas-phase equation, the second order Runge-Kutta method for liquid-phase equations and the linear interpolation between the two coordinate systems. The calculation results has shown that the characteristics of the droplet penetration and recirculation have been strongly influenced by the interaction between gas and liquid phases in such a way that most of the vaporization process has been confined to the wake region of the injector, thereby improving the flame stabilization properties of the flowfield.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권3호
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• pp.715-722
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• 2014

Three twisted rudders fit for large container ships have been developed; 1) the Z-twisted rudder that is an asymmetry type taking into consideration incoming flow angles of the propeller slipstream, 2) the ZB-twisted rudder with a rudder bulb added onto the Z-twisted rudder, and 3) the ZB-F twisted rudder with a rudder fin attached to the ZB-twisted rudder. The twisted rudders have been designed computationally with the hydrodynamic characteristics in a self-propulsion condition in mind. The governing equation is the Navier-Stokes equations in an unsteady turbulent flow. The turbulence model applied is the Reynolds stress. The calculation was carried out in towing and self-propulsion conditions. The sliding mesh technique was employed to simulate the flow around the propeller. The speed performances of the ship with the twisted rudders were verified through model tests in a towing tank. The twisted versions showed greater performance driven by increased hull efficiency from less thrust deduction fraction and more effective wake fraction and decreased propeller rotating speed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.264-269
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• 2001

Axial fans are widely used in household electrical appliances due to their easy usage and high flow rate for cooling capacity. At the same time, the noise generated by these fans causes one of serious problems. In order to calculate the noise of a fan, we develop the software IFD - Intranet Fans Design. With this software we can design, analysis the performance and predict the noise of fan. The prediction model, which allowed the calculation of acoustic pressure at the blade passing frequency and it's higher harmonic frequencies, has been developed by Lowson's equation. To calculate the unsteady resultant force of the blade, time-marching free-wake method is used. The objective of this study is to calculate the effects of number of blades, rotating velocity, and sweep angle on the noise of fan..

• International Journal of Aeronautical and Space Sciences
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• 제15권4호
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• pp.345-355
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• 2014

This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제36권8호
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• pp.728-733
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• 2008

Unsteady aerodynamic analysis of an air-pressure-levitated high-speed ground vehicle moving over the nonplanar ground surface are performed using the boundary-element method. The potential flow solution is included in a time-stepping loop and the wake is captured as part of the solution. When the vehicle moving inside the channel, the lift coefficient and the pitching moment coefficient of the vehicle are increased further because the air trapped by the channel increases the ground effect. In other words, the nonplanar ground surface such as the channel decreases further the longitudinal stability of the vehicle. On the other hand, there is little difference between the ground and the channel in the lateral stability of the vehicle because the lift increment due to the nonplanar ground surface such as the channel takes place on both sides of the wing with the same rate of increase.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.413-418
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• 2000

The noise sources from a rotating cylinder were identified to describe the blunt trailing edge noise. Firstly, LES formulation was applied to a non-orthogonal grid system and was tested with three-dimensional cross-flow over a cylinder with a yaw angle. The computed far-field noise showed peaks at Strouhal numbers ranging from 0.135 to 0.165 for the yawed cylinder flow with end-plates placed at both extremes under the yaw angle of $30^{\circ}$ and Reynolds number of $1.15{\times}10^4$. It was observed that the slantwise shedding at angles other than the cylinder yaw angle is intrinsic to inclined cylinder, with the result of shedding angles between $15^{\circ}$ and $31^{\circ}$. To study the trailing-edge wake thickness and unsteady lift-coefficient distribution in the span-wise direction of a rotating fan blade, the flows around rotating cylinder with 1,000 rpm were simulated and the far-field noise was exactly computed using the Ffowcs-Williams and Hawkings equation with quadrupole source term. The incoming velocities and stagnant zones were continuously distributed along the cylinder, and their changes made the Strouhal sheddings to occur at different phases even at almost same Strouhal number.

• Particle and aerosol research
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• 제17권4호
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• pp.81-89
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• 2021

Understanding particle-laden flow around cylindrical bodies is essential for the better design of various applications such as filters. In this study, laminar flows around two tandem cylinders and the motions of particles in the flow are numerically investigated at low Reynolds numbers. We aim to reveal the effects of the spacing between cylinders, Reynolds number and particle Stokes number on the characteristics of particle trajectories. When the cylinders are placed close, the unsteady flow inside the inter-cylinder gap at Re = 100 shows a considerable modification. However, the steady recirculation flow in the wake at Re = 10 and 40 shows an insignificant change. The change in the flow structure leads to the variation of particle dispersion pattern, particularly of small Stokes number particles. However, the dispersion of particles with a large Stokes number is hardly affected by the flow structure. As a result, few particles are observed in the cylinder gap regardless of the cylinder spacing and the Reynolds number. The deposition efficiency of the upstream cylinder shows no difference from that of a single cylinder, increasing as the Stokes number increases. However, the deposition on the downstream cylinder is found only at Re = 100 with large spacing. At this time, the deposition efficiency is generally small compared to that of an upstream cylinder, and the deposition location is also changed with no deposited particles near the stagnation point.

• Journal of the Society of Naval Architects of Korea
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• 제43권4호
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• pp.422-430
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• 2006

The horn and movable parts around the gap of the conventional semi-spade rudder are visualized by high speed CCD camera with the frame rate of 4000 fps (frame per second) to study the unsteady cavity pattern on the rudder surface and gap. In addition, the pressure measurements are conducted on the rudder surface and inside the gap to find out the characteristics of the flow behavior. The rudder without propeller wake is tested at the range of $1.0{\leq}{\sigma}_v\;1.6$ and at the rudder deflection angle of $-8{\leq}{\theta}{\leq}10^{\circ}$. The time resolved cavity images are captured and show strong cavitation around the rudder gap in all deflection angles. As the deflection angle gets larger, the flow separated from the horn surface increases the strength of cavitation. The accelerated flow along the horn decreases its pressure and the separated flow from the horn increases the pressure abruptly. The pressure distribution inside the gap reveals the flow moving from the pressure to suction side. In the negative deflection angle, the turning area on the movable part initiates the flow separation and cavitation on it.

• Journal of Advanced Marine Engineering and Technology
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• 제35권2호
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• pp.264-270
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• 2011

The Characteristics of the flowfield around three circular cylinders in tandem arrangement was investigated by PIV. Strouhal numbers, vorticity, velocity vectors and velocity profiles were observed at centre-to-centre space ratios of P/D=1.25~3.75, and Reynolds number of Re=$3.0{\times}10^3{\sim}5.0{\times}10^3$. As the results the Strouhal numbers measured in the rear region of 3rd the cylinder were distinguished three kind of regions with the space ratios and The flow pattern in the wake of each cylinder was different according to these regions. The time averaged flow at region of each cylinder was almost stagnated and the size of the stagnated region was small in order of 1st, 2nd and 3rd cylinder. The direction of vortex at the front and rear region of 2nd cylinder was opposed each other with the small difference(${\alpha}= {\pm}5^{\circ}$) of the attack angle ${\alpha}$.

• Journal of Advanced Marine Engineering and Technology
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• 제37권2호
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• pp.156-162
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• 2013

The characteristics of the unsteady flowfield of a square prism having a detached splitter plate at the wake side were investigated by advanced vortex method. The instantaneous and average velocity field and pressure field around a square prism without and having splitter plate were calculated by forcing the gap ratio having the maximum drag reduction rate, at Reynolds number $Re=1.0{\times}10^4$ and the width ratio H/B=1.0 of splitter to the prism width. The drag and lift coefficients on the square prism were also obtained. The calculated results agree with the measured drag coefficients and pressure distributions on the square prism. The vortices of the opposite direction at upside and down side of the splitter plate were generated by installing of the plate. And the drag on the square prism was decreased by increasing of the pressure of back face of the prism with the vortices.