• The KSFM Journal of Fluid Machinery
• /
• v.13 no.2
• /
• pp.41-47
• /
• 2010

The effect of incidence angle on the three-dimensional flow and aerodynamic loss in the tip leakage flow region downstream of a turbine rotor cascade has been investigated for two tip gap-to-chord ratios of h/c=0.0% (no tip gap) and 2.0%. The incidence angle is changed to be $i=-10^{\circ}$, $0^{\circ}$, and $5^{\circ}$. The results show that for $i=5^{\circ}$, secondary flows including the passage vortex are intensified noticeably, and there is a strong interaction between the passage and tip leakage vortices. For $i=-10^{\circ}$, however, the passage vortex is weakened significantly, so that there exists only a strong leakage-jet-like secondary flows near the casing wall. For h/c=0.0% and 2.0%, aerodynamic loss tends to increase with increasing i from $-10^{\circ}$ to $5^{\circ}$. A small increment of i in its positive incidence range results in a remarkable aerodynamic loss increase, while increasing i in the negative incidence range leads to a small change in the aerodynamic loss generation.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.13 no.1
• /
• pp.628-640
• /
• 2021

To investigate the supercavity geometry and gas flow structure for the supercavities with two closure types under the different flow conditions, an inhomogeneous multiphase model with the SST turbulence model was established, and validated by experimental results. The results show that two distinct regions exist inside the supercavity, which include the downstream flow region along the gas-water interface and the reverse flow region. For the twin-vortex supercavity, the internal gas leaks from the supercavity boundary by two paths: the supercavity surface and the two-vortex tubes. Increasing Froude number leads to more internal gas stripped from the supercavity surface. Two types of gas loss exist for the re-entrant jet supercavity with high Froude number, one type is the steady process of gas loss, and the major gas-leaking path is the supercavity surface rather than supercavity closure region. The other type is the unsteady periodic ejection, and the gas cluster of periodic ejection is merely a small part of the gas stored inside the supercavity.

• The Journal of the Acoustical Society of Korea
• /
• v.43 no.1
• /
• pp.103-111
• /
• 2024

Axial-flow fans are used to transport fluids in relatively low-pressure flow regimes, and a variety of design variables are employed. The tip geometry of an axial fan plays a dominant role in its flow and noise performance, and two of the most prominent flow phenomena are the tip vortex and the tip leakage vortex that occur at the tip of the blade. Various studies have been conducted to control these three-dimensional flow structures, and winglet geometries have been developed in the aircraft field to suppress wingtip vortices and increase efficiency. In this study, a numerical and experimental study was conducted to analyze the effect of winglet geometry applied to an axial fan blade for an air conditioner outdoor unit. The unsteady Reynolds-Averaged Navier-Stokes (RANS) equation and the FfocwsWilliams and Hawkings (FW-H) equation were numerically solved based on computational fluid dynamics techniques to analyze the three-dimensional flow structure and flow noise numerically, and the validity of the numerical method was verified by comparison with experimental results. The differences in the formation of tip vortex and tip leakage vortex depending on the winglet geometry were compared through a three-dimensional flow field, and the resulting aerodynamic performance was quantitatively compared. In addition, the effect of winglet geometry on flow noise was evaluated by numerically simulating noise based on the predicted flow field. A prototype of the target fan model was built, and flow and noise experiments were conducted to evaluate the actual performance quantitatively.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.10 no.3
• /
• pp.307-317
• /
• 2018

In this study, numerical investigations of the tip clearance flow characteristics of a pumpjet propulsor based on Computational Fluid Dynamics (CFD) method have been presented. The Zwart-Gerber-Belamri (Z-G-B) cavitation model based on Reynolds Averaged Navier-Stokes (RANS) method is employed. The structured gird is applied. The formation and development of the tip clearance flows has been investigated and presented. The structure of the tip leakage vortex has been shown. The radial distributions of different velocity components with different Span along the axial direction have been carried out to present the influence of the tip clearance flow on the main flow. In addition, the influences of the tip clearance size on the pumpjet propulsor performance, including the impact on the velocity flow fields and the cavitation characteristic, have been presented.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.3
• /
• pp.963-969
• /
• 1991

본 연구에서는 누설와류는 유동에 영향을 미치며 에너지 손실로 된다. 누설 와류에 의한 손실은 다른 원인에 의한 손실에 비교하여 그 비중이 크다. 따라서 누 설와류 특성을 이해하기 위해 설계영각(.alpha.=10.7˚)에서 절현비를 t/C=0.90와 2.71로 바꾸고, 또 절현비가 설계절현비 t/C=0.90일 경우에 영각을 설계 영각 .alpha.=10.7˚와 실 속점의 영각 .alpha.=18.9˚사이에서 바꾸어 회전익 후방의 회전유동장을 측정하여 누설와 류의 거동을 연구하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.13-13
• /
• 1998

A simple model of the tip leakage flow models of the rotor downstream flow is developed, based on Lakshminarayana's theoretical concept on the tip clearance flow and the experimental data published in open literature. And new spanwise distribution models of deviation angle and pressure loss coefficient due to the tip leakage flow are formulated for use in association with the streamline curvature method as a through flow analysis. Combining these new models and previous deviation and loss models due to secondary flow, a robust streamline curvature method is established for flow analysis of single-stage, subsonic axial turbines with wide ranges of turning angle, aspect ratio and blading type. At the exit from rotor rows, the flow variables are mixed radially according to a spanwise transport equation. The proposed streamline curvature method is tested against a forced vortex type turbine as well as a free vortex type one. The results show that the spanwise variations of flow angle, axial velocity and loss coefficients at rotor exit are predicted with good accuracy, being comparable to a steady three-dimensional Navier-Stokes analysis. This simple and fast flow analysis is found to be very useful for the turbine design at the initial design phase.

• Nuclear Engineering and Technology
• /
• v.52 no.8
• /
• pp.1677-1688
• /
• 2020

In the sodium-cooled fast reactor, the steam generator is a heat exchange device between sodium and water, which may cause leakage, resulting in a sodium-water reaction accident, which in turn affects the safe operation of the entire nuclear reactor. To this end, the electromagnetic vortex flowmeter is used to detect leakage of the steam generator and its signal processing method is studied in this paper. The hydraulic experiment was carried out by using water instead of liquid sodium, and the sensor output signal of the electromagnetic vortex flowmeter under different gas injection volumes was collected. The bubble noise signal is reflected by the base line of the sensor output signal. According to the relationship between the proportion of the bubble noise signal in the sensor output signal and the gas injection volume, a signal processing method based on the energy ratio calculation is proposed to detect whether the water contains bubbles. The gas injection experiment of liquid sodium was conducted to verify the effectiveness of the signal processing method in the detection of bubbles in sodium, and the minimum detectable leak rate of water in the steam generator was detected to be 0.2 g/s.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.3 no.2
• /
• pp.18-24
• /
• 2000

A two-dimensional numerical method for inviscid two-fluid flows with a significant entrainment into both directions is established, and the oil leakage from a non-pressurized underwater pipe is studied. The interface between two fluids is modeled at a vortex sheet. The flow field and the subsequent interface evolution are solved by using the vortex-in-cell method. For longer flow simulation with a realistic two fluids interaction, an efficient merging scheme is introduced. In the Boussinesq limit, the speed of the external fluid intrusion into the pipe is very close to the existing mathematical models, and the lock exchange is observed in spite of a significant roll-up of the interface and entrainments. It is believed that the developed method can be utilized effectively for further detailed studies on various two-fluid flows which are encountered in many different marine oil spill problems.

• International Journal of Aeronautical and Space Sciences
• /
• v.16 no.2
• /
• pp.157-164
• /
• 2015

The present work performs three-dimensional flow calculations based on Reynolds Averaged Navier-Stokes (RANS) and Delayed Detached Eddy Simulation (DDES) to investigate the flow field of a transonic rotor (NASA Rotor 37) at near-stall condition. It is found that the DES approach is likely to predict well the complex flow characteristics such as secondary vortex or turbulent flow phenomenon than RANS approach, which is useful to describe the flow mechanism of a transonic compressor. Especially, the DES results show improvement of predicting the flow field in the wake region and the model captures reasonably well separated regions compared to the RANS model. Besides, it is discovered that the three-dimensional vortical flows after the vortex breakdown from the rotor tip region are widely distributed and its vortex structures are clearly present. Near the rotor leading edge, a part of the tip leakage flows in DES solution spill over into next passage of the blade owing to the separation vortex flow and the backflow is clearly seen around the trailing edge of rotor tip. Furthermore, the DES solution shows strong turbulent eddies especially in the rotor hub, rotor tip section and the downstream of rotor trailing edge compared to the RANS solution.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.8
• /
• pp.1015-1022
• /
• 2003

Flows in a regenerative pump were calculated for several flow-rates, using the CFX-Tascflow. The calculated results show the vortex structure in the impeller and side channel. The predicted performance shows considerable discrepancy from the measured values for low flow rates. Main source of the difference is the leakage flow of pump strongly affecting the performance of pump. A simple correlation was proposed using calculated leakage flows through the simplified passage. One dimensional analysis were made for the recirculating flow and angular momentum transfer using calculated three dimensional data base.