Numerical Analysis of Cavitation Instabilities Arising in the Three-Blade Cascade

2004 ◽  
Vol 126 (3) ◽  
pp. 419-429 ◽  
Author(s):  
Yuka Iga ◽  
Motohiko Nohml ◽  
Akira Goto ◽  
Toshiaki Ikohagi
Keyword(s):  
Numerical Method ◽  
High Speed ◽  
Homogeneous Model ◽  
Rotating Stall ◽  
Two Phase ◽  
Wide Range ◽  
Phase Medium ◽  
Long Time ◽  
Entire Flow ◽  
Locally Homogeneous

Three types of cavitation instabilities through flat plate cascades, which are similar to “forward rotating cavitation,” “rotating-stall cavitation” and “cavitation surge” occurring in high-speed rotating fluid machinery, are represented numerically under the three-blade cyclic condition. A numerical method employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to solve the above flow fields, because this permits the entire flow field inside and outside the cavity to be treated through only one system of governing equations. In addition, the numerical method suites to analyze unsteady cavitating flow with a long time evolution. From the calculated results of the present numerical simulation with wide range of cavitation number and flow rate, we obtain a cavitation performance curve of the present three-blade cyclic cascade, analyze the aspects of unsteady cavitation, and discuss the characteristics and mechanisms of cavitation.

A Pressure-Base One-Fluid Compressible Formulation for High Speed Two-Phase Flows With Heat and Mass Transfer

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Yan Luo ◽  
Jianqiu Zhou ◽  
Xia Yang ◽  
Zhanxiang Jiang
Keyword(s):  
Numerical Method ◽  
High Speed ◽  
Immiscible Fluids ◽  
Numerical Results ◽  
Cavitating Flows ◽  
Two Phase Flows ◽  
Two Phase ◽  
Two Phases ◽  
Locally Homogeneous ◽  
Homogeneous Media

This paper presents a numerical method for high-speed compressible cavitating flows. The method is derived from one-fluid formulation in a sense that the two phases are well mixed and the mixture is considered as a locally homogeneous media. Energy equation is solved to predict the temperature evolution which is then used together with pressure to update the density field. A volume of fluid (VOF) phase-fraction based interface capturing approach is used to capture the phase front between the two immiscible fluids. The derived formulations have been implemented into a pressure-based, segregated algebraic semi-implicit compressible solver in Openfoam, which can be used to solve for high-speed compressible two-phase flows involving phase changing. Numerical examples include the cavitating flows induced by an ultrasonic oscillating horn with and without a counter sample. The numerical results by the proposed method are validated against the published experimental data as well as numerical results and good agreements have been obtained. Our calculation demonstrates that the proposed numerical method is applicable to the study of high-speed two phase flows with phase transition and wave propagation, such as shock waves induced by the collapse of the cavitation bubbles.

scholarly journals Numerical Study of Sheet Cavitation Breakoff Phenomenon on a Cascade Hydrofoil

2003 ◽  
Vol 125 (4) ◽  
pp. 643-651 ◽  
Author(s):  
Yuka Iga ◽  
Motohiko Nohmi ◽  
Akira Goto ◽  
Byeong Rog Shin ◽  
Toshiaki Ikohagi
Keyword(s):  
Numerical Study ◽  
Dominant Role ◽  
Homogeneous Model ◽  
Cavity Surface ◽  
Cavity Flows ◽  
Two Phase ◽  
Sheet Cavitation ◽  
Phase Medium ◽  
Flow Through ◽  
Locally Homogeneous

Two-dimensional unsteady cavity flow through a cascade of hydrofoils is numerically calculated. Particular attention is focused on instability phenomena of a sheet cavity in the transient cavitation condition, and the mechanism of the breakoff phenomenon is examined. TVD-MacCormack’s scheme employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to analyze the cavity flows. The present method permits us to treat the entire cavitating/noncavitating unsteady flowfield. By analyzing the numerical results in detail, it becomes clear that there are at least two mechanisms in the breakoff phenomenon of the sheet cavity: one is that re-entrant jets play a dominant role in such a breakoff phenomenon, and the other is that pressure waves propagating inside the cavity bring about another type of breakoff phenomenon accompanying with cavity surface waves.

Numerical Modeling of Hydrodynamic Impact and Local Slamming Effects

2015 ◽  
Author(s):  
Ali Mohtat ◽  
Ravi Challa ◽  
Solomon C. Yim ◽  
Carolyn Q. Judge
Keyword(s):  
Numerical Method ◽  
Impact Velocity ◽  
High Speed ◽  
Impact Behavior ◽  
Analytical Prediction ◽  
Arbitrary Lagrangian Eulerian ◽  
Hydrodynamic Impact ◽  
Ale Formulation ◽  
Wide Range ◽  
The Impact

Numerical simulation and prediction of short duration hydrodynamic impact loading on a generic wedge impacting a water free-surface is investigated. The fluid field is modeled using a finite element (FE) based arbitrary Lagrangian-Eulerian (ALE) formulation and the structure is modeled using a standard Lagrangian FE approximation. Validation of the numerical method against experimental test data and closed form analytical solutions shows that the ALE-FE/FE continuum approach captures the impact behavior accurately. A detailed sensitivity analysis is conducted to study the role of air compressibility, deadrise angle, and impact velocity in estimation of maximum impact pressures. The pressure field is found to be insensitive to air compressibility effect for a wide range of impact velocities and deadrise angles. A semi-analytical prediction model is developed for estimation of maximum impact pressures that correlates deadrise angle, impact velocity, and a nonlinear interaction term that couples hydrodynamic effects between these parameters. The numerical method is also used to examine the intrinsic physics of water impact on a high-speed planing hull with the goal of predicting slamming loads and resulting motions.

Experimental Adiabatic Two-Phase Pressure Drops of R134a, R236fa and R245fa in Small Horizontal Circular Channels

2011 ◽  
Author(s):  
Chin L. Ong ◽  
John R. Thome
Keyword(s):  
Pressure Drop ◽  
Flow Boiling ◽  
Homogeneous Model ◽  
Prediction Methods ◽  
Two Phase ◽  
Pressure Drops ◽  
Wide Range ◽  
Small Channels ◽  
Experimental Pressure ◽  
Phase Pressure

Experimental adiabatic two-phase pressure drops data for refrigerants R134a, R236fa and R245fa during flow boiling in small channels with internal diameters of 1.03, 2.20 and 3.04 mm are presented. The main purpose was to investigate the effects of channel confinement on adiabatic two-phase pressure drops. Thus, the two-phase pressure drop trends were systematically investigated over a wide range of test conditions for all three refrigerants and channel sizes. Statistical comparisons have also been made by comparing the experimental pressure drop data database with various macroscale and microscale prediction methods from the literature. The comparison showed relatively moderate accuracy for three prediction methods developed for macroscale flows, i.e. Baroczy and Chisholm, Friedel and the homogeneous model with the Cicchitti et al. viscosity relation. As for microscale prediction methods, the Cioncolini et al. annular flow model worked best with 68.5% of the data within ± 30%, followed by the Sun and Mishima and the Zhang et al. methods. Combining this database with the LTCM lab’s earlier database for 0.509 and 0.790 mm channels, there appears to be no evidence of a macro-to-microscale transition, at least with respect to two-phase pressure drops.

Study of Thermodynamic Effect On the Mechanism of Flashing Flow Under Pressurized Hot Water by a Homogeneous Model

2021 ◽  
Author(s):  
Anh Dinh Le
Keyword(s):  
Numerical Method ◽  
Saturated Vapor ◽  
Homogeneous Model ◽  
Temperature Drop ◽  
Numerical Data ◽  
Hot Water ◽  
Two Phase ◽  
Suppression Effect ◽  
Flow Parameters ◽  
Thermodynamic Effect

Abstract The flashing flow in a Moby_Dick converging-diverging nozzle under pressurized hot water from 460.5 K to 483.5 K is simulated using a homogeneous compressible water-vapor two-phase flow model. The kinematic and thermodynamic mass transfer are accessed using the cavitation model based on the Hertz-Knudsen-Langmuir equation. Our simplified thermodynamic model is coupled with the governing equations to capture the phase-change heat transfer. This numerical method proved its reliability through a comparison with available experimental data of flow parameters inside the nozzle. Consequently, the present numerical method shows good potential for simulating the flashing flow under pressurized hot water conditions. The satisfying prediction of averaged flow parameters with a slight improvement compared to reference numerical data is reproduced. The results confirm a noticeable impact of the thermodynamic effect on the mechanism of flashing flow, resulting in a considerable decrease in the flow temperature and the saturated vapor pressure. The flashing non-equilibrium is significantly decreased, forcing the flashing flow to be classified as the usual cavitation behavior and better suited to homogeneous model. While the temperature drop is highly dependent on evaporation, the thermodynamic suppression is influenced by the condensation. The suppression effect, unobserved in water at a lower temperature in previous studies, is noticeable for the pressurized hot water flow characterized by the cavitation mechanism. The vapor void fraction decreased considerably in the radial and axial directions as the water temperature rose to 483.5 K in this study.

Spatial Correlation Based Stall Inception Analysis

2007 ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris
Keyword(s):  
Spatial Correlation ◽  
High Speed ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Fourier Decomposition ◽  
Stall Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Wide Range ◽  
Response Pressure

Investigations of stall inception and compressor pre-stall behavior have used a variety of techniques to make inferences about the mechanisms of rotating stall inception. Many of these techniques utilized data from arrays of circumferentially spaced hot-wires or high frequency response pressure transducers. This paper presents results from the application of several typical analysis techniques to the interpretation of unsteady casing pressure measurements recorded during two representative stall event in a high-speed axial compressor stage. Results from visual pressure trace inspection, spatial Fourier decomposition, wavelet filtering, and traveling wave energy techniques are presented and compared. The effects of measurement and analysis parameters are also briefly discussed. A new analysis technique based on windowed two-point spatial correlation between adjacent stall inception sensors is described. The method was found to provide both spatial and temporal information about rotating features in the compressor flow and is insensitive to low pass filtering and parameter selection over a wide range of values. It was also found to be valuable for analysis of both pre-stall and stall inception behavior.

Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes

2004 ◽  
Vol 126 (1) ◽  
pp. 107-118 ◽  
Author(s):  
J. L. Pawloski ◽  
C. Y. Ching ◽  
M. Shoukri
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range ◽  
Flow Regime Maps

The void fractions, flow regimes, and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. A capacitance sensor for instantaneous void fraction measurements was developed. The mean and probability density function of the instantaneous void fraction signal can be used to effectively identify the different flow regimes. The current flow regime data show significant differences in the transitional boundaries of the existing flow regime maps. Property correction factors for the flow regime maps are recommended. The pressure drop measurements were compared to the predictions from four existing two-phase flow pressure drop models. Though some of the models performed better for certain flow regimes, none of the models were found to give accurate results over the entire range of flow regimes.

scholarly journals Synchronized Multiple Drop Impacts into a Deep Pool

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 141 ◽  
Author(s):  
Manfredo Guilizzoni ◽  
Maurizio Santini ◽  
Stephanie Fest-Santini
Keyword(s):  
Fluid Dynamics ◽  
High Speed ◽  
Laboratory Experiments ◽  
Distilled Water ◽  
Single Drop ◽  
Two Phase ◽  
Wide Range ◽  
Computational Fluid Dynamics Cfd ◽  
Drop Impacts ◽  
The Impact

Drop impacts (onto dry or wet surfaces or into deep pools) are important in a wide range of applications, and, consequently, many studies, both experimental and numerical, are available in the literature. However, such works are focused either on statistical analyses of drop populations or on single drops. The literature is heavily lacking in information about the mutual interactions between a few drops during the impact. This work describes a computational fluid dynamics (CFD) study on the impact of two, three, and four synchronized drops into a deep pool. The two-phase finite-volume solver interFoam of the open source CFD package OpenFOAM® was used. After validation with respect to high speed videos, to confirm the performance of the solver in this field, impact conditions and aspects that would have been difficult to obtain and to study in experiments were investigated: namely, the energy conversion during the crater evolution, the effect of varying drop interspace and surface tension, and multiple drop impacts. The results show the very significant effect of these aspects. This implies that an extension of the results of single-drop, distilled-water laboratory experiments to real applications may not be reliable.

Analysis of Cavitating High Speed Liquid Flow Through a Converging-Diverging Nozzle

2015 ◽  
Author(s):  
William E. Asher ◽  
Steven J. Eckels
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Power Plants ◽  
Control Volume ◽  
Homogeneous Model ◽  
Cavitating Flow ◽  
Shear Stresses ◽  
Variable Cross ◽  
Two Phase ◽  
Integral Forms

Cavitation is an important and common phenomena in fluid flow in which a fluid becomes two-phase through pressure variation. In devices such as valves, orifices, and metering devices, as well as loss of coolant situations in power plants, cavitation can be of interest due to erosion, energy efficiency, safety, and other concerns. It is possible for a cavitating flow to become sonic, accelerating and imposing additional energy losses that would not have occurred had the flow remained below the speed of sound. Models of this aspect of two-phase flow have not been fully explored and often have only been developed for the case of constant area. In the present paper, the homogeneous equilibrium model is developed by applying the integral forms of the conservation of mass, momentum, and energy equations to a control volume of variable cross-sectional area with adiabatic walls. The developed model is then applied to experimental data with R-134a as the fluid of interest for an instrumented converging-diverging nozzle for which mass flow, pressure, and temperature are measured. Applying the model to the experimental data yields interesting results in both the relationship between velocity and void fraction and in the predicted shear stresses down the length of the nozzle. The model predicts negative shear stresses near the nozzle’s throat an order of magnitude higher than those seen elsewhere in the nozzle. For this reason, the homogeneous model is likely not sufficient to accurately describe this variant of cavitating flow.

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