Numerical Analysis of 2-D Unsteady Cavitating Flow Around Hydrofoils in Cascade.

Trans. Japan Soc. Aero. S Sci.

Yoshida

2011

Self Cite

Cavitation is an inevitable phenomenon that occurs when improvements such as performance enhancement and weight reduction are made to the turbopump in liquid-propellant rocket engines. Unsteady cavitation may cause oscillations (cavitation instabilities) in the turbopump. Accurate prediction and efficient suppression of cavitation instabilities are important for designing turbopumps. We performed a numerical simulation of the unsteady cavitation in tandem cascades and compared the results with those obtained for a single-stage cascade. The type of cavitation instability could be controlled by changing the front-and rear-blade chord lengths. When the clearance gap between the front and rear blades was located near the cascade throat entrance, rotating-stall conditions could be easily achieved, even at high flow rates. Cavitation surge and super-synchronous and sub-synchronous rotating cavitations were suppressed when the clearance gap was located at 40% of the total chord length. When the clearance gap was located inside the cascade throat, cavitation reached a steady state at the ' value where the cavity length equaled the front-blade length; then, cavitation instabilities and unsteady cavitation were suppressed in the low-' region. When the clearance gap was located at 80% of the total chord length, cavitation surge was completely suppressed, although rotating cavitation occurred over a larger region.

Section: Cavitation Modelmentioning

confidence: 99%

Section: Cavitation Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Numerical Analysis of Controlling Cavitation Instabilities in Tandem Cascades

Trans. Japan Soc. Aero. S Sci.

Yoshida

2011

Self Cite

“…3, No. 2, 2008 have developed numerical method for cavitation which is suitable for unsteady calculation [4], reproduced frequency characteristics and clarified two kinds of mechanisms of break-off phenomenon of sheet cavitation in cascade [5]. And the authors have succeeded in reproduction of three kinds of cavitation instabilities simultaneously by numerical analysis of three blades cascade without adding a model or boundary condition for individual phenomena [6].…”

Section: Journal Of Environment and Engineeringmentioning

confidence: 99%

Numerical Analysis of Cavitation Instabilities and the Suppression in Cascade

Hiranuma

Yoshida³

et al. 2008

JEE

Self Cite

In this study, unsteady cavitation and cavitation instabilities are numerically analyzed around flat-plate cascade with three blades cyclic condition in water / air working fluid. The numerical method employing an original model "locally homogeneous model of compressible gas-liquid two-phase medium" is applied to numerical simulation. The method can simply treat the entire flow field inside and outside the cavity by one system equations. As a result of numerical analysis, occurrence and oscillation characteristics of three types of cavitation instabilities are reproduced, which are "cavitation surge", "super-synchronous rotating cavitation" and "rotating-stall cavitation". Additionally, flow fields around flat-plate cascade with slits on blades are analyzed in the conditions where the cavitation instabilities arise in the cascade without slit. Consequently, the suppression effect of the slit on the cavitation instabilities is confirmed.

“…In the previous study, the present authors developed a numerical method for simulating cavitation that is suitable for unsteady calculation (4) . In addition, we have reproduced the frequency characteristics of the break-off phenomenon of sheet cavitation and have clarified two mechanisms of the break-off phenomenon in the cascade (5) .…”

Section: Introductionmentioning

confidence: 99%

Occurrence Mechanism and Oscillation Characteristics of Pulsation Phenomenon Arising in Cavitation Surge in Cascade

Hashizume

Yoshida

et al. 2009

JEE

Self Cite

In this study, numerical analysis of cavitating three-blade cyclic flat-plate cascade is performed with paying attention to cavitation surge which is a type of cavitation instabilities. A numerical method employing "locally homogeneous model for compressible gas-liquid two-phase medium" is applied to solve the unsteady cavitating flowfield. From results of numerical analysis, few typical tendency of cavitation surge which is well known in experiments was reproduced numericaly, that frequency of cavitation surge decreases with lowering σ, and that cavitation surge is easy to occur at low flow rate condition. Additionaly, mechanism of pulsation phenomenon of cavitation surge in flat-plate cascade was clarified, that collapse pressure of cloud cavity in downstream of cascade propagates upstream on contact with re-entrant jet which is flowing backward inside a sheet cavity and causes oscillation in upstream pressure, also that negative angle of attack and choking of cascade throat are considered to cause of oscillation in flow rate. About dynamic transfer function of cavitation, certain degree of possibility is confirmed in quasi-steady mass flow gain factor M quasi and cavitation compliance K quasi for prediction of occurrence limit of cavitation instabilities. Additionally, for prediction of frequency of cavitation surge, it was confirmed that local cavitation compliance K local is more available than quasi-steady one.