• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.33-39
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• 2008

To improve the mixing efficiency and to reduce the pressure loss, it is needed to develope a new mixing device for supersonic combustion. The vent mixer is introduced as the new supersonic fuel-air mixer. Computational analyses, that include pressure profile, density contour, and streamline tracing, have been carried out. The expansion wave generates at the end of the extended upper wall of the mixer. And it reduces the shock wave from the hole. Incoming air flow through the hole makes several recirculation regions which increase the mixing efficiency, and the separation region at the downward wall expends the boundary layer which reduces the pressure loss.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.381-386
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• 2007

Jet-A spray, evaporation and combustion were numerically analyzed in annular type model combustor using KIVA-3V. Liquid fuel's atomizing was affected by flow field near droplet. When cooling flow was not optimized, SMD was increased, and equivalence ratio was horizontally distributed in combustor's downstream. Flame spread out horizontally and separated in combustors downstream. Flame center was separated by cooling flow. Flame separation made local high temperature in downstream that caused NO increase.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.363-366
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• 2011

Mixing and combustion experiments with a vent slot mixer were performed in Mach 2 supersonic wind tunnel. Helium and hydrogen gases each were used for the mixing and the combustion experiment with a plasma jet (PJ) torch. The vent slot mixer holds plenty of fuel in the downstream mixing region, even though the fuel is transversely injected. In case of the combustion, the injected fuel is ignited by the PJ torch, and then unburned mixture is burned by shock-induced combustion downstream. Thermal choking in the combustor leads to shock trains in the isolator, causing the unstable combustion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.7
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• pp.469-478
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• 2019

Multirotor configurations such as VTOL and urban air mobility have been focused on today due to the high maneuverability. Aerodynamic and aeroacoustic characteristics of multirotor have much difference to those of a single rotor. In this study, a numerical analysis based on the free wake vortex lattice method is used for identifying the wake interaction effect. In order to compare the various configurations and operating conditions, the effects of the spacing between the rotors in hovering flight and the effects of the advancing ratio and the formation in forward flight are discussed. In the hovering flight, the unsteady loading of multirotor changes periodically and loading fluctuation increases as decreasing the spacing. It causes the variation in unsteady loading noise and the noise directivity pattern. In the forward flight, the difference in loading fluctuation and noise characteristics are observed according to the diamond and square formation of rotors. By comparing with results of single rotor analysis, multirotor configurations have different directivity pattern and amplitude of loading noise according to the location of each rotor. As a result, wake interaction effect becomes a highly important factor for aerodynamic and aeroacoustic analysis according to multirotor configurations and operating conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1218-1225
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• 2002

Large-scale vortical structure of a turbulent separation bubble affected by unsteady wake is essential to understand flow mechanisms in various fluid devices. A spoked-wheel type of wake generator provides unsteady wake, which modifies the turbulent separation bubble significantly by changing rotation directions and passing frequencies. A detailed mechanism of vortex shedding from the separation bubble with unsteady wake is analyzed by taking a conditional average with spatial box filtering, which spatially integrates measured signals at pre-determined wavelength. A convecting nature of the large-scale vortical structure is analyzed carefully. Spatial evolution of the large-scale vortical structure with frequency variance is also exemplified.

• Journal of Energy Engineering
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• v.10 no.3
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• pp.223-232
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• 2001

To study the stabilization characteristics of diffusion flame formed in the wake of a cylindrical bluff body with fuel injection, the flame stability limits, length and temperature of recirculation zone of flame, turbulence intensity distribution near the recirculation zone of flame were measured and analyzed. The length of recirculation zone is independent on main fuel injection quantity, but it is dependent on fuel injection angles, air stream velocity, and auxiliary fuel injection into recirculation zone. For diffusion flame, in general, the flame stabilization is deteriorated with increase of he length of recirculation zone, but if the turbulence generator is installed, the flame stabilization is improved with increase of the length of recirculation zone. The temperature of recirculation zone is dependent on fuel injection angles, auxiliary fuel injection into recirculation zone, turbulence generators, and it dependent on fuel injection angles, auxiliary fuel injection into recirculation zone, turbulence generators, and it has a maximum value at the condition of each theoretical mixture. In general, the more temperature of recirculation zone is low, the more flame is stable. But when the turbulence generator is installed, the more temperature of recirculation zone is low, the more flame is unstable. The turbulence intensity in the wake of bluff body is increased with increase of diameter or blockage ratio of grid. The more turbulence intensity is increased by installation of turbulence generator, the more flame is unstable. Finally, It is clear that the stabilization characteristics of diffuser flame can be controlled by some parameters such as fuel injection angles, auxiliary fuel injection into recirculation zone, turbulence generators.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1171-1179
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• 2008

LES analysis was conducted with in-house CFD code to investigate the turbulence evolution and interaction due to turbulence ring and splash plate in the gas generator. The calculation results show that the installation of turbulence ring can introduce additional turbulences and significantly improve turbulent mixing in the downstream flow. However, the addition of splash plate in the downstream of TR(Turbulence Ring) brings totally different shape of perturbation energy and enstrophy distribution into turbulent mixing. This enhancement can be done by the formation of the intensively strong vorticity and mixing behind the plate. Pressure drop was found to be a reasonable level of about 1% or less of initial pressure in all calculation cases. Also, calculation results revealed that the variation of shape and intrusion length of TR did not greatly affect the characteristics of turbulent mixing in the chamber. Even though the effect of installation location of splash plate on the turbulent mixing was not investigated yet, calculation results conclude the addition of splash plate leads to the increase in turbulent mixing with an acceptable pressure drop.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.615-626
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• 2009

The objective of this study is to investigate the interference effects due to tandem rotor's overlap in the forward flight. To resolve the instabilities caused by close proximity of the wake to the blade surface, the field velocity approach is implemented to the existing unsteady panel code coupled with a time-marching free wake model. The modified code is then used to investigate the effects of the selected parameters on the forward flight performance of the tandem rotor. The calculated results for rotor separation effect indicate that stagger(d/D) appears to have little effects on the forward flight performance at high advance ratio and the square of gap(H/D) is inversely proportional to overlap induced power factor. In addition, it is also shown that the overlap induced power factor increases to a certain extent and decrease back as the advance ratio increases.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.209-215
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• 2017

A large floating offshore wind-wave hybrid power generation system with an area of 150 m2 and four 3 MW class wind turbine generators was installed at each column top. In accordance with the wind turbine arrangement, the wake generated from upstream turbines can adversely affect the power performance and load characteristics of downstream turbines. Therefore, an optimal arrangement design, obtained through a detailed flow analysis focusing on wake interference, is necessary. In this study, to determine the power characteristics and annual energy production (AEP) of individual wind turbines, transient computational fluid dynamics, considering wind velocity variation (8 m/s, 11.7 m/s, 19 m/s, and 25 m/s), was conducted under different platform conditions ($0^{\circ}$, $22.5^{\circ}$, and $45^{\circ}$). The AEP was calculated using a Rayleigh distribution, depending on the wind turbine arrangement. In addition, we suggested an optimal arrangement design to minimize wake losses, based on the AEP.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.97-103
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• 2003

Numerical research has been done for the transverse jet behind a rearward-facings step in turbulent supersonic flow without chemical reaction. Purpose of transverse jet is to enhance mixing of the fuel in the combustor. Two-dimensional unsteady flowfields generated by slot injection into supersonic flow are numerically simulated with the Navier-Stokes equations with two-equation k-$\varepsilon$ turbulence model. Numerical method is used high-order upwind TVD scheme. Eight cases are computed for different slot momentum flux ratios and slot position at downstream of the step. The flow is very similar to the cavity flow, because the jet acts as an obstacle. The numerical results thus show the periodic phenomenon.