• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.295-310
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• 2015

In the present study, an unstructured mixed mesh flow solver was used to conduct a numerical prediction of the aerodynamic performance of the S-76 rotor in hover. For the present mixed mesh methodology, the near-body flow domain was modeled by using body-fitted prismatic/tetrahedral cells while Cartesian mesh cells were filled in the off-body region. A high-order accurate weighted essentially non-oscillatory (WENO) scheme was employed to better resolve the flow characteristics in the off-body flow region. An overset mesh technique was adopted to transfer the flow variables between the two different mesh regions, and computations were carried out for three different blade configurations including swept-taper, rectangular, and swept-taper-anhedral tip shapes. The results of the simulation were compared against experimental data, and the computations were also made to investigate the effect of the blade tip Mach number. The detailed flow characteristics were also examined, including the tip-vortex trajectory, vortex core size, and first-passing tip vortex position that depended on the tip shape.

• 한국전산유체공학회지
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• 제21권2호
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• pp.62-69
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• 2016

It has been highly demanded to improve the accuracy of CFD(Computational Fluid Dynamics) methods for the assessment of the hydrodynamic performance of marine propellers in cavitating and non-cavitating flows. This paper presents a validation study on the numerical simulation of the tip vortex flow of a non-cavitating marine propeller SVA VP1304. The calculations are carried out by using the Reynolds averaged Navier-Stokes(RANS) approach, where the Reynolds Stress Model(RSM) is used for turbulence closure. The present paper contains a grid dependence test for the propeller open water simulations and a special emphasis is placed on conducting a local grid adaptation on the blade tip and in the tip vortex to reasonably reproduce the velocity and the pressure in the tip vortex flow field. The numerical results are compared with the experimental validation data, which are published in the second International Symposium on Marine Propulsors 2011(SMP'11). The present numerical results show a reasonable agreement with the experiments.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.291-292
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• 2006

Currently A demand of high precision workpiece is increasing in industry. At present, roundness measuring machine using Air bearing, coordinate measuring machine that are used from measurement station. but these machines will not be able to apply to In-line process. because of like these machine's price are very expensive and measurement time is long. also, the complexity of conventional roundness measurement method based on fourier transform, it makes difficult to development analysis program. This work present new architecture of a Out-diameter measuring system fur analysis of roundness of product. In this system, the influence of table motion errors is minimize by using two LVDT sensor and knife edge contact tip. We are produce a test machine and make an experimenter on Out-diameter of test bearing. The measurement result compared with roundness measuring machine.

• 대한조선학회논문집
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• 제46권6호
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• pp.569-577
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• 2009

As the scale factor of model propellers utilized in cavitation test is about 40, it is difficult to find out practical countermeasures against the small area erosions on the blade tip region throughout model erosion tests. In this study, a partial propeller blade model was used for the observation of cavitation pattern for the eroded propeller. A partial propeller blade model was manufactured from 0.7R to tip with expanded profile and with adjustable device of angle of attack. Reynold's number of a partial propeller blade model is 7 times larger than that of a model propeller. Also, anti-singing edge and application of countermeasures to partial propeller blade model which produced in large scale can be more practical than a model propeller. For the observation of cavitation at high Reynold's number, high speed cavitation tunnel was used. To find out the most severe erosive blade position during a revolution, cavitation observation tests were carried out at 5 blade angle positions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.639-644
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• 2002

In this paper, a successful noise reduction of an axial flow fan for a refrigerator is presented. The vortex sheet generated at the blade tip of fan was suppressed by changing the shape of the tip. The structure of vortex sheet and detailed flow pattern around the fan were studied by two-dimensional LDV(Laser-Doppler Velocimetry). Effective ways to work out the result as mentioned above are to make the tip of the blade varied in thickness and to have elliptical shapes. To seek the optimal value fur the shape of new fan, several cases were examined. Through the application of the methods, the refrigerator became less noisy by 3.8 dB(A) in terms of air-borne noise produced only by the axial flow fan compared to the current one.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.85-91
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• 2012

Numerical simulations on a single stage transonic compressor which is developed by Korea Aerospace Research Institute are carried out and their results are compared with experimental data for cross validations. Comparisons between experimental data and numerical simulation results show good agreements on a performance curve, static pressure and total pressure distributions. CFD results show that there is a clear interaction between tip leakage flow and normal shock in the rotor passage. Tip leakage flows are almost dissipated after the strong normal shock and it forms a strong recirculation near the blade tip. Also a large separation region grows on the suction surface just after the normal shock. As the pressure ratio and blade loading increase, the normal shock line moves upstream and it starts to deviate from the blade leading edge. Then the tip leakage flow does not overcome the strong adverse pressure gradient and flow blockage originated from the tip recirculation region. As a result, the tip leakage flow heads for the neighboring blade leading edge, which results in a compressor stall.

• 한국생산제조학회지
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• 제20권6호
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• pp.679-684
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• 2011

Recently, STS 301L joints of side panels to frames for stainless steel rolling stock have been made out by using existing welding methods including Resistance Spot Welding, Laser Welding and Arc Welding. Most of the processes were jointed by spot welding because it is faster at welding and comparatively less expensive for investment in welding facilities than other methods. During spot welding, however, indentation of the metal surface was made due to pressure and melting property of welding. Moreover, since the melting metal was forced to periphery of the plate as indentation was made, sheet separation, which cracked apart between jointed sheets, was carried out. A slight deformation which resulted from sheet separation deteriorated the emotional quality of railway vehicles. This paper suggests that by processing conventional spot electrode tip appropriately, melting metal is able to push up around the processed part (Hollow Spot Electrode Tip) and prevent from being dislodged from first place to periphery. Consequently, sheet separation is remarkably decreased. Also, the emotional quality of appearance of stainless steel rolling stock is enhanced considerably.

• 대한기계학회논문집A
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• 제27권2호
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• pp.223-230
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• 2003

Stress patterns are created in the plastic spur gear tooth body by introducing a hole or a steel pin to improve stress distribution. Static analysis using finite element method is carried out to show the effect. The result shows that maximum stress as well as tooth tip displacement is dependent on the size and location of a hole or a steel pin. When a hole located on the tooth center line, the maximum static stress level and the tooth tip deflection is always higher than that of a solid gear. But, a considerable reduction in the maximum stress and tooth tip displacement is achieved by insertion of steel pin.

• 대한조선학회논문집
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• 제51권3호
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• pp.259-264
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• 2014

Tip vortex cavitation (TVC) is important for naval ships and research vessels that require raising the cavitation inception speed to maximum possible values. The concepts for alleviating the tip vortex are summarized by Platzer and Souders (1979), who carried out a thorough literature survey. Active control of TVC involves the injection of a polymer or water from the blade tip. The main effect of such mass injection (both water and polymer solutions) into the vortex core is an increase in the core radius, consequently delaying TVC inception. However, the location of the injection port needs to be selected with great care in order to ensure that the mass injection is effective in delaying TVC inception. In the present study, we propose a semi-active control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semi-active control is that because of its flexibility, the attached thread can be sucked into the low-pressure region closer to the vortex core center. An experimental study using a scale model was carried out in the cavitation tunnel at the Seoul National University. It was found that a flexible thread can effectively suppress the occurrence of TVC under the design condition for a model propeller.

• 대한기계학회논문집B
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• 제27권12호
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• pp.1750-1757
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• 2003

This paper describes the flow measurements inside the blade passage of an axial flow fan by using a rotating hot-wire probe sensor from a relative flame of reference fixed to the rotor blades. The validity of fan rotor designed by a streamline curvature equation was performed by the measurement of the three-dimensional flow upstream and downstream of the fan rotor using a 5-hole pitot tube. The vortical flow structure near the rotor tip can be clearly observed by the measurements of a relative velocity and its fluctuation on quasi-orthogonal planes to a tip leakage vortex. Larger vortical flow, which results in higher blockage in the main flow, is formed according to decrease a flow rate. The vortical flow spreads out to the 30 percent span from the rotor tip at near stall condition. In the design operating condition, the tip leakage vortex is moved downstream while the center of the vortex keeps constant in the spanwise direction. Detailed characteristics of a velocity fluctuation with relation to the vortex were also analyzed.