• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.25-30
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• 2012

Renewable energy has been interested because of fluctuation of oil price, depletion of fossil fuel resources and environmental impact. Amongst renewable energy resources, hydropower is most reliable and cost effective way. In this study, to develop a new type of micro hydro turbine which can be operated in the range of very low specific speed, a cross-flow hydro turbine with simple structure is proposed. The turbine is designed to be used at the very low specific speed range of hydropower resources, such as very high-head and considerably small-flow rate water resources. CFD analysis on the performance and internal flow characteristics of the turbine is conducted to obtain a practical data for the new design method of the turbine. Results show that optimized arrangement of guide vane angle and inner guide angle can give contribution to the turbine performance improvement.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.21-28
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• 2007

The ratio of disk friction loss in a centrifugal pump is very large for the total pump loss in the range of very low specific speed. Therefore, impeller radius should be shortened to increase the pump efficiency because the disk friction loss is proportional to the fifth power of impeller radius. In order to compensate the decreased head by the shortened impeller radius, vane angle at impeller outlet should be increased. However, as the vane angle at impeller outlet becomes larger, performance instability occurs at low flow rate regions. In this study, J-Groove is adopted to suppress the performance instability and detailed examination is performed for the influence of the J-Groove on the pump performance. The results show that J-Groove gives good effect on the suppression of performance instability. Moreover, as J-Groove increases pump head considerably, the pump size can be smaller for head requirements.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.3
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• pp.404-412
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• 2008

As a suitable volute configuration in the range of low specific speed, circular casing is suggested in this study. The internal flows in a centrifugal pump with the circular and spiral casings are measured by PIV and analyzed by CFD. The results show that the head and efficiency of the pump by a circular casing of very small radius are almost same as those by the spiral casing. Even at the best efficiency point, the internal flow of the pump by circular casing is asymmetric, and vortex and strong secondary flow occurs in the impeller passage. The radial velocity becomes higher remarkably only near the region of the discharge throat. The flow in the impeller outlet is strongly controlled by the circular casing because the velocity distribution almost does not affected by the position of the impeller blades.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.2
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• pp.284-290
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• 2006

For the case of high head and critical low flow rate range of micro hydropower resources, it requires very low specific speed turbines which are lower than conventional impulse turbine's specific speed. In order to satisfy the request for very low specific speed turbine with high efficiency, a new positive displacement turbine is developed. The performance characteristics of the new turbine is tested and compared with a conventional impulse turbine, which is used for automatic water faucet system. The purpose of present study is to develop an high performance turbine that can be used to extract micro hydropower potential of a water supply system. The test results show that the positive displacement turbine is much more efficient than the conventional turbine and it can sustain high efficiency under the wide range of operating conditions. The pressure pulsations at the inlet and outlet of the positive displacement turbine can be considerably minimized by using simple pressure damper.

• New & Renewable Energy
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• v.20 no.2
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• pp.35-43
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• 2024

A pump turbine is a technically matured option for energy production and storage systems. At the off-design operating range, the pump turbine succumbed to flow instabilities, which correlated with the pump turbine geometry. A low specific speed pump turbine was designed and modified according to the impeller blade angle. Reynolds-Average Navier-Stokes is carried out with a shear stress transport turbulence model to evaluate the detailed flow characteristics in the pump turbine. The impeller blade inlet angle (𝛽₁) and outlet angle (𝛽₂) are used to evaluate hydraulic loss in the pump turbine. When 𝛽₁ changed from low to high value, the maximum efficiency is increased by 4.75% in turbine mode. The S-Curve inclination is reduced by 8% and 42% for changes in 𝛽₁ and 𝛽₂ from low to high values, respectively. At α = 21°, the shock loss coefficient (𝜁_s) is reduced by 16% and 19% with increases of 𝛽₁ and 𝛽₂ from low to high values, respectively. When 𝛽₁ and 𝛽₂ values increased from low to high, the impeller friction coefficient (𝜁_f) increased and decreased by 20% and 8%, respectively. Hence, the high 𝛽₂ effectively reduced the loss coefficient and S-Curve inclination.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.237-243
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• 2002

A centrifugal compressor of 50HP for reverse brayton cryocooler using neon as a coolent has been developed. It has relatively low total-to-total pressure ratio but mass flow rate is very small and the voting gas, neon, has greater specific heat ratio than air. It was essential to have very high rotational speed of 100,000 RPM. The efficiency of compressor has great effects on overall system and the COP of cryocooler. To meet the design requirement of the compressor efficiency and to minimized the required rotational speed, highly efficiency impeller having low specific speed was designed. To maintain the overall system efficient high, gas bearing of bump type and high speed permanent magnet synchronus motor was developed and adopted. In this paper, design and performance prediction results of the compressor impeller is presented.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1607-1613
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• 2008

The present investigate is a base investigate required in development of DMT wagon train. And it deduced that follows by developing trail analysis model about Modalohr wagon train and examining traveling movement specific using analysis model developed. Vibration acceleration of all direction was increased with addition of travel speed and first suspension. But in case of right and left vibration acceleration, that could influenced by nonlinear specific of first suspension. Therefore checking about those is needed. Frequency of $2{\sim}3\;Hz$ and $7{\sim}8\;Hz$ generated in Right and left, up, down vibration of vehicle. And right and left vibration of bogie generated $25{\sim}35\;Hz$ in low speed section and frequency of $40{\sim}50\;Hz$ in high speed section, $25{\sim}35\;Hz$ in low speed section, $10{\sim}15$ or $40{\sim}50\;Hz$ in high speed section.

• The KSFM Journal of Fluid Machinery
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• v.9 no.1 s.34
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• pp.9-18
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• 2006

In the range of very low specific speed ($n_s<0.25$, non-dimensional), the performance of a centrifugal pump is much different from that of a centrifugal pump of normal ns and the efficiency of the pump drops rapidly with the decrease of $n_s$. In order to examine the reason of unstable performance characteristics of the very low $n_s$- centrifugal pump, the internal flow of the pump with a semi-open impeller is measured by a PTV(Particle Tracking Velocimetry) system. The purpose of this study is to make clear the internal flow characteristics and to obtain basic knowledge of the pump performance. The results show that the leakage flow through tip clearance give a strong effect on the flow pattern of impeller passage. A large vortex in the impeller passage and a strong reverse flow at impeller outlet are formed in the range of small flow rates, and the vortex and the reverse flow together reduce the absolute tangential velocity at the impeller outlet and cause the performance instability.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.181-191
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• 2006

The most common kind of vehicular accident is the low-speed rear-end impact that result in high portion of insurance claims and Whiplash Associated Disorders(WAD). The low-speed collisions have specific characteristics that differ from high speed collisions and must be treated differently This paper presents a simple continuous contact force model for the low-speed rear-end impact to simulate the accelerations, velocities and the contact force as functions of time. A smoothed Coulomb friction force is used to represent the effect of braking, which was found to be significant in simulating low-speed rear end impact. The intervehicular contact force is modeled using nonlinear damping and spring elements with coefficients and exponents. This paper presents how to estimate analytically stiffness and damping coefficients. The exponent of the nonlinear contact force model was determined to match the overall acceleration pulse shape and magnitude. The model can be used to determine ${\Delta}Vs$ and peak accelerations for the purpose of accident reconstruction and for injury biomechanics studies.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.1-10
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• 2006

An optimization study on a small turbopump impeller operating at the low specific speed is conducted to obtain high output head at the impeller exit. Its specific speed in SI unit (RPM, m3/sec, m) is 4.0, and the outer diameter is 56mm. On the optimization, the outer diameter of the impeller is maintained constant to restrict the pump size, and an objective function of pressure head is maximized with eight design variables, which are related with designing an impeller shape. The response surface method is used to the optimization scheme, and the commercial code CFX-10 is applied for numerical analysis. The pressure head of the objective function obtained with an optimized impeller is increased by 9.7% compared with that obtained on an impeller designed with typically recommended design parameters. This increment is caused by reducing the recirculation region within the impeller passage.