Numerical Analysis of the Influence of Acceleration on Cavitation Instabilities that arise in Cascade

Iga, Yuka,Konno, Tasuku Korean Society for Fluid machinery 2012 International journal of fluid machinery and syste Vol.5 No.1

In the turbopump inducer of a liquid propellant rocket engine, cavitation is affected by acceleration that occurs during an actual launch sequence. Since cavitation instabilities such as rotating cavitations and cavitation surges are suppressed during launch, it is difficult to obtain data on the influence of acceleration on cavitation instabilities. Therefore, as a fundamental investigation, in the present study, a three-blade cyclic cascade is simulated numerically in order to investigate the influence of acceleration on time-averaged and unsteady characteristics of cavitation that arise in cascade. Several cases of acceleration in the axial direction of the cascade, including accelerations in the upstream and downstream directions, are considered. The numerical results reveal that cavity volume is suppressed in low cavitation number condition and cavitation performance increases as a result of high acceleration in the axial-downstream direction, also, the inverse tendency is observed in the axial-upstream acceleration. Then, the regions in which the individual cavitation instabilities occur shift slightly to a low-cavitation-number region as the acceleration increases downstream. In addition, in a downstream acceleration field, neither sub-synchronous rotating cavitation nor rotating-stall cavitation are observed. On the other hand, rotating-stall cavitation occurs in a relatively higher-cavitation-number region in an upstream acceleration field. Then, acceleration downstream is robust against cavitation instabilities, whereas cavitation instabilities easily occur in the case of acceleration upstream. Additionally, comparison with the Froude number under the actual launch conditions of a Japanese liquid propellant rocket reveals that the cavitation performance will not be affected by the acceleration under the current launch conditions.

Numerical Analysis of the Influence of Acceleration on Cavitation Instabilities that arise in Cascade

Yuka Iga,Tasuku Konno 한국유체기계학회 2012 International journal of fluid machinery and syste Vol.5 No.1

In the turbopump inducer of a liquid propellant rocket engine, cavitation is affected by acceleration that occurs during an actual launch sequence. Since cavitation instabilities such as rotating cavitations and cavitation surges are suppressed during launch, it is difficult to obtain data on the influence of acceleration on cavitation instabilities. Therefore, as a fundamental investigation, in the present study, a three-blade cyclic cascade is simulated numerically in order to investigate the influence of acceleration on time-averaged and unsteady characteristics of cavitation that arise in cascade. Several cases of acceleration in the axial direction of the cascade, including accelerations in the upstream and downstream directions, are considered. The numerical results reveal that cavity volume is suppressed in low cavitation number condition and cavitation performance increases as a result of high acceleration in the axial-downstream direction, also, the inverse tendency is observed in the axial-upstream acceleration. Then, the regions in which the individual cavitation instabilities occur shift slightly to a low-cavitation-number region as the acceleration increases downstream. In addition, in a downstream acceleration field, neither sub-synchronous rotating cavitation nor rotating-stall cavitation are observed. On the other hand, rotating-stall cavitation occurs in a relatively higher-cavitationnumber region in an upstream acceleration field. Then, acceleration downstream is robust against cavitation instabilities, whereas cavitation instabilities easily occur in the case of acceleration upstream. Additionally, comparison with the Froude number under the actual launch conditions of a Japanese liquid propellant rocket reveals that the cavitation performance will not be affected by the acceleration under the current launch conditions.

Numerical Analysis of Liquid Droplet Impingement on Pitted Material Surface with Water Pool of Various Depth

Hirotoshi Sasaki,Yuka Iga 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4

Liquid droplet impingement erosion occurs at the elbows in steam pipes where droplets impinge at high speed. In the actual pipe wall which numerous droplets always impinge, it is predicted that both a liquid film exists on a pipe wall surface and, on the other hand, this surface is also eroded by repeated droplet impingement. Therefore, the liquid film and roughness on the material surfaces are considered to exist mixed on the actual impinged point of droplets. In this study, by using an in-house fluid/material two-way coupled numerical method that considers reflection and transmission on the fluid/material interface, the numerical analysis of the phenomenon of liquid droplet impingement on a pitted surface with a water pool is conducted. From the analysis results, the impinged pressure at the moment of impingement is reduced by a water pool. However, as the cavitation bubbles are generated in the bottom and top of the droplet after the impingement and then the cavitation bubble of the bottom side collapses, the collapse pressure which greatly exceeds the pressure of the droplet impingement occurs, and the equivalent stress also increases greatly there. Therefore, this analysis result may indicate one reason why the erosion progresses deeply at the pit part in an actual pipe wall thinning.

Erratum : Numerical Analysis of Damping Effect of Liquid Film on Material in High Speed Liquid Droplet Impingement

Sasaki, Hirotoshi,Ochiai, Naoya,Iga, Yuka Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.2

Thermodynamic Effect of Tip-Leakage-Vortex Cavitation on Two-dimensional Hydrofoils with Tip Clearance for Hot Water

Donghyuk Kang,Daichi Nakai,Yuka Iga 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4

Investigation of the thermodynamic effect of tip-leakage-vortex cavitation on a two-dimensional hydrofoil designed with a tip clearance for hot water is reported herein. During unsteady cavitation of water maintained at 90 °C (hereinafter referred to as hot water), the observed decrease in temperature in the tip-leakage region was greater compared to that in the mid-span region. In contrast, during supercavitation of hot water, the situation was reversed (i.e., the temperature decrease in the tip-leakage region was smaller than that in the mid-span region). The cavitation-pattern map for hot water was observed to be largely similar to that for water maintained at 30 °C (hereinafter referred to as tepid water). On the other hand, the amplitude of the dominant frequencies of unsteady cavitation of the hot water was observed to be greater than that of the cavitation of tepid water owing to the sudden collapse of cloud cavitation.

Numerical Analysis of Damping Effect of Liquid Film on Material in High Speed Liquid Droplet Impingement

Sasaki, Hirotoshi,Ochiai, Naoya,Iga, Yuka Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.1

By high speed Liquid Droplet Impingement (LDI) on material, fluid systems are seriously damaged, therefore, it is important for the solution of the erosion problem of fluid systems to consider the effect of material in LDI. In this study, by using an in-house fluid/material two-way coupled method which considers reflection and transmission of pressure, stress and velocity on the fluid/material interface, high-speed LDI on wet/dry material surface is simulated. As a result, in the case of LDI on wet surface, maximum equivalent stress are less than those of dry surface due to damping effect of liquid film. Empirical formula of the damping effect function is formulated with the fluid factors of LDI, which are impingement velocity, droplet diameter and thickness of liquid film on material surface.

Numerical Analysis of Damping Effect of Liquid Film on Material in High Speed Liquid Droplet Impingement

Hirotoshi Sasaki,Naoya Ochiai,Yuka Iga 한국유체기계학회 2016 International journal of fluid machinery and syste Vol.9 No.1

By high speed Liquid Droplet Impingement (LDI) on material, fluid systems are seriously damaged, therefore, it is important for the solution of the erosion problem of fluid systems to consider the effect of material in LDI. In this study, by using an in-house fluid/material two-way coupled method which considers reflection and transmission of pressure, stress and velocity on the fluid/material interface, high-speed LDI on wet/dry material surface is simulated. As a result, in the case of LDI on wet surface, maximum equivalent stress are less than those of dry surface due to damping effect of liquid film. Empirical formula of the damping effect function is formulated with the fluid factors of LDI, which are impingement velocity, droplet diameter and thickness of liquid film on material surface.