• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.202-212
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• 2008

A three-dimensional computation was conducted to understand effects of the low Reynolds number on the loss characteristics in a transonic axial compressor, Rotor67. As a gas turbine becomes smaller in size and it is operated at high altitude, the operating condition frequently lies at low Reynolds number. It is generally known that wall boundary layers are thickened and a large separation occurs on the blade surface in axial turbomachinery as the Reynolds number decreases. In this study, it was found that the large viscosity did not affect on the bow shock at the leading edge but significantly did on the location and the intensity of the passage shock. The passage shock moved upstream towards leading edge and its intensity decreased at the low Reynolds number. This change had large effects on the performance as well as the internal flows such as the pressure distribution on the blade surface, tip leakage flow and separation. The total pressure rise and the adiabatic efficiency decreased about 3% individually at the same normalized mass flow rate at the low Reynolds number. In order to analyze this performance drop caused by the low Reynolds number, the total pressure loss was scrutinized through major loss categories such as profile loss, tip leakage loss, endwall loss and shock loss.

• The KSFM Journal of Fluid Machinery
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• v.5 no.2 s.15
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• pp.7-14
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• 2002

The effect of tip clearance is important part for turbomachinery performance. Tip leakage flow due to tip clearance is mixed with passage vortex. Large amount of loss is generated at the mixing region and overall performance of turbomachinery is reduced. Numerical calculation of the 1st stage rotor of GE7FA gas turbine is carried out to investigate tip clearance effect on performance, pitchwise variations of velocity profiles, pressure distributions and loss coefficients. A commercial code, CFX-TascFlow is validated in this study.

• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.36-42
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• 2004

The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

• The KSFM Journal of Fluid Machinery
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• v.5 no.3 s.16
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• pp.15-24
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• 2002

This paper presents an experimental study on the unsteady flow phenomena such as leakage flow and rotating stall which have influences on the performance and stability of an axial flow fan. For this study, unsteady pressure were measured using high frequency pressure transducers mounted on the easing wall of rotor passage and analyzed by Double Phase-Locked Averaging Technique. As the flow rate was reduced to near stall point, the pressure difference between the pressure and the suction side of the blade was increased especially new the leading edge and the lowest pressure zone of suction side was gradually developed. From the result of unsteady pressure field on the casing wall, one period of rotating stall was divided into three zones and the flow characteristics on each zone were described in detail.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.399-406
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• 2014

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a turbine blade equipped with both a pressure-side winglet and a suction-side squealer have been measured for the tip gap-to-span ratio of h/s = 1.36%. The suction-side squealer has a fixed height-to-span ratio of $h_s/s$ = 3.75% and the pressure-side winglet has width-to-pitch ratios of w/p = 2.64%, 5.28%, 7.92% and 10.55%. The results are compared with those for a plane tip and for a cavity squealer tip of $h_{ps}/s$ = 3.75%. The present tip delivers lower loss in the passage vortex region but higher loss in the tip-leakage vortex region, compared to the plane tip. With increasing w/p, its mass-averaged loss tends to be reduced. Regardless of w/p, the present tip provides lower loss than the plane tip but higher loss than the cavity squealer tip.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.243-249
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• 2001

Steady state flow calculations are executed for turbo-pump inducers of modem design to validate the performance of Tascflow code. Hydrodynamic performance is evaluated and structure of the passage flow and leading edge recirculation are also investigated. Calculated results show good coincidence with experimental data of static pressure performance and velocity profiles over the leading edge. Upstream recirculation, tip leakage and vortex flow at the blade tip and near leading edge are main source of pressure loss. Amount of pressure loss from the upstream to the leading edge corresponds to that of pressure loss through the whole blade. The total viscous loss is considerably large due to the strong secondary flow.

• The KSFM Journal of Fluid Machinery
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• v.5 no.2 s.15
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• pp.22-28
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• 2002

Steady state flow calculations are conducted for the newly-designed turbo-pump inducers to validate the performance of Tascflow code. Hydrodynamic performance is evaluated, and structures of the passage flow and leading edge recirculation are also investigated. The calculated results show good coincidence with the experimental data of the static pressure performance and velocity profiles near the leading edge. Upstream recirculation, tip leakage and vortex flow at the blade tip and near leading edge are main sources of pressure losses. Amount of pressure losses from the upstream to the leading edge corresponds to that of pressure losses through the whole blade. The total viscous losses are considerably large due to the strong secondary flow.

• International Journal of Fluid Machinery and Systems
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• v.8 no.3
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• pp.193-201
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• 2015

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up.

• International Journal of Fluid Machinery and Systems
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• v.8 no.4
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• pp.274-282
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• 2015

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up.