• International Journal of Fluid Machinery and Systems
• /
• v.2 no.2
• /
• pp.165-171
• /
• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.22 no.3
• /
• pp.465-471
• /
• 2013

Flow rate control is the uppermost concern for a trochoid hydraulic pump. Cavitation within the flow field of the pump has the greatest effect on the flow control during high-speed pump rotation of approximately 3500~4000 RPM. In this paper, based on AMESim$^{(R)}$ and Solid Works$^{(R)}$, we will present a method to simulate cavitation by analyzing the control factors of a trochoid pump, including the hydraulic pressure change at the outlet, flow rate based on the rotation speed of the inner rotor, leakage through the gap between the outer and inner rotors, and discharging angle of the outlet. The proposed methodology of the [cavitation simulation will enable field engineers to more easily design trochoid pumps, and will allow more concrete control over the flow rate of the pump by realizing an analysis model similar to the actual product model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.648-654
• /
• 2011

The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.169-177
• /
• 2005

A high resolution scheme for solving gas-liquid two-phase flows with cavitation is described. This scheme uses the curvilinear coordinate grid and solves the density based momentum equations for mixture of gas-liquid medium with a preconditioning method to treat both compressible and incompressible flow characteristics. The present preconditioned method is based on the Runge-Kutta explicit finite-difference scheme, and is improved by using the diagonalization, the flux difference splitting and the MUSCL-TVD schemes to save computational effort and to increase stability and resolvability, especially at gas-liquid contact surfaces. A homogeneous equilibrium cavitation model is used to treat the gas-liquid two-phase medium in cavitating flow as a locally homogeneous pseudo-single-phase medium. Therefore, it is easy to solve cavitating flow, including wave propagation, large density changes and incompressible flow characteristic at low Mach number. Some numerical results obtained by the present scheme are shown.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2483-2488
• /
• 2008

To mitigate the effects of cavitation and flashing, several types of orifices have been installed in the pipeline of new nuclear power plants. To review the effects of wall thinning caused by flow-accelerated corrosion by the types of orifices, which are cone and plate, and the relation between flow behavior and local wall thinning, experiments and numerical analyses for the downstream pipe of two types of orifices were performed. The experimental results in terms of static pressure obtained for the experimental facilities were compared with those of three-dimensional (3D) numerical analyses using the FLUENT code. As the results of review of flow-accelerated corrosion effects based on the experiment and numerical analysis, it was identified that the orifice of cone-type can be comparatively mitigated the effects of cavitation and flashing, but can not be mitigated the effect of flow-accelerated corrosion.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.569-572
• /
• 2002

In the present study, flow simulations of a solution pump fer an absorption chiller are performed. The results are compared to the experimental data. Since the cavitation is more likely to occur in a solution pump due to Its operation under vacuum condition, and the cavitation was not considered in the present computations, the computed and experimental results show large discrepancies. For more accurate performance prediction of a solution pump, a cavitation model is required in the flow simulation. Flows through an inducer are also studied to see the effect of design parameters on performance characteristics. It is shown from the results that, if not properly designed, recirculation legion may exist near the hub region of the Inducer, and the suction surface may experience higher pressure than the pressure surface of the inducer, which may deteriorate the performance.

• Journal of computational fluids engineering
• /
• v.16 no.1
• /
• pp.60-66
• /
• 2011

Engineering interests of submerged bodies and turbomachinery has led researchers to study various cavitation models for decades. The governing equations used for the present work are the two-phase Navier-Stokes equations with homogeneous mixture model. The solver employed on implicit dual time preconditioning algorithm in curvilinear coordinates. Three different cavitation models were applied to two axisymmetric cylinders and compared with experiments. It is concluded that the Merkle's new cavitation model has successfully accounted for cavitating flows and well captured the re-entrant jet phenomenon over the 0-caliber cylinder.

• The KSFM Journal of Fluid Machinery
• /
• v.7 no.1 s.22
• /
• pp.45-50
• /
• 2004

Two phenomena often encountered in liquid flow, which were completely absent in gas or vapor flow, were cavitation and flashing. These phenomena were of significant interest in any comprehensive discussion of control valves or contracted devices since their occurrence would affect the device sizing procedures, might introduce noise and vibration, and also may limit the life expectancy of device components and the immediate downstream piping. Thus, this study aimed to find the reduction method of occurred cavitation in system by the computer simulation. A derivative six model with different dimensions of cavity were adopted. From the results, it was found that the length of the cavity was mote important factor to reduce the pressure drop over the control valves or contracted devices than the depth of the cavity. And the pressures along the centerline of the contracted devices were dropped two times in the case of haying the large length (Lc=1.5D) of cavity.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.1
• /
• pp.130-137
• /
• 2019

In this study, a centrifugal seawater cooling pump was analyzed to investigate its cavitation behavior over different operating flow rates. 3D two-phase simulations were carried out with ANSYS-CFX commercial code. The $k-{\varepsilon}$ turbulence and Rayleigh-Plesset cavitation models were employed in the simulations. A head drop characteristics curves for three discharge rates was built based on numerical predictions. At higher flow rates, the impeller was more vulnerable to bubble cavitation. The 3 % head drop points of the pump working at 0.7Q, Q, and 1.3Q (Q: design flow rate) corresponded with NPSHa 1.21 m, 1.83 m, and 3.45 m, respectively. The volume of vapor bubbles was estimated and cavitation locations were anticipated to visualize the development of the cavity within the impeller. Moreover, the distribution of pressure coefficient and a blade loading chart are specifically presented, bringing out the harmful impacts of cavitation on the pump operation.

• Journal of computational fluids engineering
• /
• v.19 no.2
• /
• pp.17-23
• /
• 2014

Cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency in devices, such as propellers, pump impellers, nozzles, injectors, torpedoes, etc. Thus, the cavitating flow simulation is of practical importance for many engineering systems. In the present work, a two-phase flow solver based on the homogeneous mixture model has been developed. The solver employs an implicit preconditioning, dual time stepping algorithm in curvilinear coordinates. The flow characteristics around Clark-Y hydrofoil were calculated and then validated by comparing with the experimental data. The lift and drag coefficients with changes of angle of attack and cavitation number were obtained. The results show that cavity length and lift, drag coefficient increase with increasing angle of attack.