• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.229-234
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• 2017

In this study, TiAl alloy was fabricated by a centrifugal casting method for turbo charge of automotive. Optimum conditions for defectless morphology using various ceramic mold were investigated. The crystal structure, microstructure, and chemical composition of the TiAl prepared by centrifugal casting were studied by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS), microvickers hardness analyzer (HV). Two kinds of dendrite structures were observed with 4-fold and 6-fold symmetries. The FE-SEM, EDS and HV examinations of the as-cast TiAl showed that the thickness of the oxide layer (${\alpha}$-case) was typically less than $50{\mu}m$.

• International Journal of Fluid Machinery and Systems
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• v.5 no.2
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• pp.65-71
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• 2012

The objective of the present investigation is to explore the possibility of improving the performance of a centrifugal fan at low Reynolds numbers using a simple passive means, namely Gurney flap (GF). GFs of 1/$8^{th}$ inch brass angle (3.175 mm) corresponding to 15.9% of blade exit height or 5.1% of blade spacing at the impeller tip are attached to the impeller blade tip on the pressure surface. Performance tests are carried out on the centrifugal fan with vaneless diffuser at five Reynolds numbers (viz., 0.30, 0.41, 0.55, 0.69, $0.82{\times}10^5$, i.e., at five speeds respectively at 1,100, 1,500, 2,000, 2,500 and 3,000 rpm) without and with GF. Static pressures on the vaneless diffuser hub and shroud are also measured for each speed at four flow coefficients [${\phi}$=0.23 (below design flow coefficient), ${\phi}$=0.34 (design flow coefficient), ${\phi}$=0.45 (above design flow coefficient) and ${\phi}$=0.60 (above design flow coefficient)] with and without GF. From the performance curves it is found that the performance of the fan improves considerably with GFs at lower Reynolds numbers and improves marginally at higher Reynolds number. Similar improvements are observed for the static pressures on the diffuser hub and shroud. The effect of Reynolds number on the performance and static pressures is considerable. However the effect is reduced with GFs.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.103-109
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• 2016

With the rapid increase in the number of patients with cardiopulmonary diseases, more cardiopulmonary circulatory assist devices are also needed. These devices can be employed when heart and/or lung function poorly. Due to the critical role they take, these devices have to be designed optimally from both mechanical and biomechanical aspects. This paper presents the CFD results of a baseline model of a centrifugal blood pump for the ECMO condition. The details of flow characteristics of the baseline model together with the performance curves and the modified index of hemolysis(MIH) are investigated. Then, the geometry of baseline impeller and the volute are modified in order to improve the biomechanical performance and reduce the MIH value. The numerical simulations of two cases represent that when impeller radius and prime volume decrease the MIH value also decreases. In addition, the modified geometry shows more uniform pressure distribution inside the volute. The findings provide valuable information for further modification and improvement of centrifugal blood pumps from both mechanical and biomechanical aspects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.321-327
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• 2016

This paper presents the application of airfoil impeller for enhancement of aerodynamic performance of a high speed centrifugal fan. Three airfoil impellers are proposed, considering the maximum thickness and the location of maximum thickness of the airfoil. C4 airfoil thickness distribution is applied to the three airfoil impellers. The impellers are evaluated using CFD (computational fluid dynamics) and suction power test. From the results, it is confirmed that flow separations on the pressure side of the impeller blades and the pressure side of diffuser blades are reduced when airfoil blade is applied to the impellers. It is also confirmed that with the centrifugal fan having airfoil impellers, there is an increase in fan efficiency by approximately 3% and reduction in specific sound level by approximately 1.3 dB(A).

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.185-192
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• 2004

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB (A) and the 2$\^$nd/ BPF is reduced about 20 dB (A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.357-363
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• 2016

In this study, we perform a series of aero-thermo-mechanical analyses to predict the running-tip clearance and the effects of impeller deformation on the performance using a centrifugal compressor. During operation, the impeller deformation due to a combination of the centrifugal force, aerodynamic pressure and the thermal load results in a non-uniform tip clearance profile. For the prediction, we employ the one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The predicted running tip clearance shows a non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height occurred at the leading and trailing edges of the impeller. Because of the reduction of the tip clearance, the tip leakage flow decreased by 19.4%. In addition, the polytrophic efficiency under operating conditions increased by 0.72%. These findings confirm that the prediction of the running tip clearance and its impact on compressor performance is an important area that requires further investigation.

• Steel and Composite Structures
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• v.35 no.1
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• pp.61-76
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• 2020

In this paper, the dynamic behaviour of an inclined functionally graded material (FGM) beam with different boundary conditions under a moving mass is investigated based on the first-order shear deformation theory (FSDT). The material properties vary continuously along the beam thickness based on the power-law distribution. The system of motion equations is derived by using Hamilton's principle. The finite element method (FEM) is adopted to develop a general solution procedure. The moving mass is considered on the top surface of the beam instead of supposing it on the mid-plane. In order to consider the Coriolis, centrifugal accelerations and the friction force, the contact force method is used. Moreover, the effects of boundary conditions, the moving mass velocity and various material distributions are studied. For verification of the present results, a comparative fundamental frequency analysis of an FGM beam is conducted and the dynamic transverse displacements of the homogeneous and FGM beams traversed by a moving mass are compared with those in the existing literature. There is a good accord in all compared cases. In this study for the first time in dynamic analysis of the inclined FGM beams, the Coriolis and centrifugal accelerations of the moving mass are taken into account, and it is observed that these accelerations can be ignored for the low-speeds of the moving mass. The new provided results for dynamics of the inclined FGM beams traversed by a moving mass can be significant for the scientific and engineering community in the area of FGM structures.

• Particle and aerosol research
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• v.15 no.4
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• pp.139-148
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• 2019

This study was performed for the application of a high-speed centrifugal cyclone to shale gas mining process. This device uses the centrifugal force to control particles similar to typical cyclones, and the disk located inside the cyclone is forced to rotate using a motor. The pressure difference occurred during the rotating of disk. Hence, inflow rate was generated without a blower fan. In addition, flow rate increased with elevating rpm of motor. The installing the disk in multiple stages on the inner rotor increased the instantaneous disk outlet flow. Hence, the control efficiency of oil particle increased from 1.05% to 31.2%. By modifying the structure of the disk so that the air flow to the opposite direction of the cyclone, the control efficiency of oil particles increased to 81.5%. By increasing the capacity of the motor and the size of the disk, the flow rate was increased to 2.5 ㎥/min because the rpm of motor and pressure difference increased. As rpm of motor increased, the cut-off diameter (d_pc) became smaller. Unlike the Lapple's equation, d_pc was inversely proportional to the effective number of rotations (N_e). The control efficiency was maintained even if the concentration of oil particles increased, for this reason, the higher the oil concentration, the more particles were accumulated and controlled.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.159-169
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• 2002

The present study investigates in detail the combined effects of the Coriolis and centrifugal farce on the development of laminar flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a rotating curved region, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal farce due to the curvature of U-bend. When the values of Rossby number and curvature ratio are large, the flow field in a rotating U-bend can be represented by two dimensionless parameters ; the Dean number K$\_$LC/=Re/√λ and a body ratio F=λ/Po. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards, the directions of the two secondary flows are the same. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct with a larger f7c. On the other hand, in case of negative rotation, where two farces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.5
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• pp.424-432
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• 2011

Shape parameters and design variables for a centrifugal compressor impeller were investigated for optimizing a centrifugal compressor. In order to compare the performance of an optimized impeller with the performance of the original impeller, an already tested impeller was chosen and design variables for optimization were selected. The meridional shapes at the shroud and at the hub were re-designed using the Bezier curve. The camber-lines of the impeller blade at the hub and at the tip were also expressed by the Bezier curve. The shape curves for impeller could be expressed using 6-8 control points. Among them, eight control points which have strong effect to the shape can be selected as design variables for optimization. Therefore, any impeller which is expressed by data points for its shape can be optimized using few design variables.