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.

Development and Validation of a Three-Dimensional Multiphase Flow CFD Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines

2012 ◽  
Author(s):  
Stephan Uhkoetter ◽  
Stefan aus der Wiesche ◽  
Michael Kursch ◽  
Christian Beck
Keyword(s):  
Experimental Data ◽  
Multiphase Flow ◽  
Gas Turbines ◽  
High Speed ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Journal Bearings ◽  
Heavy Duty ◽  
Present Contribution ◽  
Two Phase

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach including cavitation and air entrainment for high-speed turbo-machinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty type gas turbine journal bearings.

Analysis of the Variable Cross-Section Duct and Straightening Device Geometry Effects on the Hydrogen Combustion Process

2021 ◽  
pp. 62-71
Author(s):  
O.V. Guskov ◽  
V.S. Zakharov ◽  
Minko
Keyword(s):  
Combustion Chamber ◽  
Cross Section ◽  
High Speed ◽  
Power Plants ◽  
Combustion Process ◽  
Variable Cross Section ◽  
Hydrogen Combustion ◽  
Variable Cross ◽  
Calculation Methods ◽  
Transition Channel

The development and research of high-speed aircrafts and their individual parts is an urgent scientific task. In the scientific literature there is information about the integral characteristics of aircrafts of this type, but there is no detailed consideration of such an important part as the transition channel between the air intake and the combustion chamber. The article considers several flow path configurations. The numerical simulation results of hydrogen combustion in the channels of variable cross section using a detailed kinetic mechanism are presented. Based on the analysis of the data obtained, the models of the transition channel and the combustion chamber showing the best characteristics were selected. The impulse and the fuel combustion efficiency are used as criteria for comparing the flow paths. The difference in the application of two calculation methods is described. The presented results and calculation methods can be used at the stage of computational research of the working processes in advanced power plants.

scholarly journals Calculations of the pressure drop in the natural circulation boiler evaporator

2018 ◽  
Vol 240 ◽  
pp. 05009 ◽  
Author(s):  
Slawomir Grądziel ◽  
Karol Majewski
Keyword(s):  
Pressure Drop ◽  
Power Plants ◽  
Graphical Method ◽  
Natural Circulation ◽  
Homogeneous Model ◽  
Phase Slip ◽  
Two Phase Flows ◽  
Two Phase ◽  
Pressure Losses

The paper presents different models used to determine pressure losses in two-phase flows: the homogeneous model, the Lockhart-Martinelli, the Friedel and the Chisholm phase-slip models and the Martinelli-Nelson graphical method. The pressure losses are calculated for the evaporator of an OP-210 boiler with the output of 210×103 kg/h operating in one of the Polish power plants. The results obtained by means of the presented models are compared to each other.

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.

Numerical and experimental study of heat transfer in gas-solid flow: Particle cooling

2012 ◽  
Vol 3 (1) ◽  
pp. 21-29
Author(s):  
S. M. El-Behery ◽  
W. A. El-Askary ◽  
M. H. Hamed ◽  
K. A. Ibrahim
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Experimental Study ◽  
High Speed ◽  
Solid Phase ◽  
Ideal Gas ◽  
Particle Rotation ◽  
Two Phase ◽  
Solid Flow ◽  
Speed Flow

Abstract Heat transfer in gas-solid two-phase flow is investigated numerically and experimentally. The numerical computations are carried out using four-way coupling Eulerian-Lagrangian approach. The effects of particle rotation and lift forces are included in the model. The gas-phase turbulence is modeled via low Reynolds number k-ε turbulence models. The SIMPLE algorithm is extended to take the effect of compressibility into account. The experimental study is performed using crushed limestone to simulate the solid phase. The effects of Reynolds numbers, particles size and temperature on the pressure drop and the temperature of the phases are investigated. The model predictions are found to be in a good agreement with available experimental data for high speed gas-solid flow and present experimental data for low speed flow. The present results indicate that heat transfer in gas solid flow can be modeled using ideal gas incompressible flow model at low conveying speed, while for high speed flow, a full compressible model should be used.

Numerical Analysis of Super-Cavitating Flow Around a Two-Dimensional Cavitator Geometry

2011 ◽  
Author(s):  
Sunho Park ◽  
Shin Hyung Rhee
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Cavity Length ◽  
Stokes Equations ◽  
Cavitating Flow ◽  
The Body ◽  
Computational Method ◽  
Computational Results ◽  
Two Dimensional ◽  
Cell Counts

Mostly for military purposes, which require high speed and low drag, super-cavitating flows around under-water bodies have been an interesting, yet difficult research subject for many years. In the present study, high speed super-cavitating flow around a two-dimensional symmetric wedge-shaped cavitator was studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To verify the computational method, flow over a hemispherical head-form body was simulated and validated against existing experimental data. Through the verification tests, the appropriate selection of domain extents, cell counts, numerical schemes, turbulence models, and cavitation models was studied carefully. A cavitation model based on the two-phase mixture flow modeling was selected with the standard k-epsilon model for turbulence closure. The cavity length, surface pressure distribution, and the flow velocity at the interface were compared with experimental data and analytic solutions. Various computational conditions, such as different wedge angles and caviation numbers, were considered for super-cavitating flow around the wedge-shaped cavitator. Super-cavitation begins to form in the low pressure region and propagates downstream. The computed cavity length and drag on the body were compared with analytic solution and computational results using a potential flow solver. Fairly good agreement was observed in the three-way comparison. The computed velocity on the cavity interface was also predicted quite closely to that derived from the Bernoulli equation. Finally, comparison was made between the computational results and cavitation tunnel test data, along with suggestions for cavitator designs.

Investigation of Rod Vibrations in Droplet Two-Phase Flows

2011 ◽  
Author(s):  
Yoshiteru Komuro ◽  
Zensaku Kawara ◽  
Tomoaki Kunugi
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Nuclear Power ◽  
Power Plants ◽  
Motion Tracking ◽  
High Speed Camera ◽  
Two Phase Flows ◽  
Two Phase ◽  
Wet Condition ◽  
Flow Induced Vibrations

Flow-induced vibrations are important problems in nuclear power plants from the view point of reactor safety. In the investigations of these vibrations especially those induced by two-phase flows, a numerical simulation plays a significant role, so it is necessary to obtain the experimental datasets that can validate the results of the numerical simulation. This paper deals with the experimental data of one-end-supported rod vibration, and focuses on the differences between the rod vibrations induced by single-phase air flows and those induced by droplet two-phase flows. In the experiments, the displacement of the non-supported end of the test rod was visualized by the high speed camera with high spatial and temporal resolutions, namely 9.5 μm and 500 μsec. Using an image analyzing software, the rod vibration displacements were measured by the motion tracking method. The curved surface of the rod was observed by another high speed camera and the relationship between the rod vibrations and the wet condition on the surface of the rod was investigated. In addition, the vibrations measured by the strain gages and those by the high speed camera were compared to discuss the differences in these two ways of the measurements.

scholarly journals Prediction of Flow Regimes and Thermal Hydraulic Parameters in Two-Phase Natural Circulation by RELAP5 and TRACE Codes

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Viet-Anh Phung ◽  
Pavel Kudinov
Keyword(s):  
Experimental Data ◽  
Flow Regime ◽  
High Speed ◽  
Single Channel ◽  
Flow Instability ◽  
Natural Circulation ◽  
Flow Regimes ◽  
Base Case ◽  
Hydraulic Parameters ◽  
Two Phase

In earlier study we have demonstrated that RELAP5 can predict flow instability parameters (flow rate, oscillation period, temperature, and pressure) in single channel tests in CIRCUS-IV facility. The main goals of this work are to (i) validate RELAP5 and TRACE capabilities in prediction of two-phase flow instability and flow regimes and (ii) assess the effect of improvement in flow regime identification on code predictions. Most of the results of RELAP5 and TRACE calculation are in reasonable agreement with experimental data from CIRCUS-IV. However, both codes misidentified instantaneous flow regimes which were observed in the test with high speed camera. One of the reasons for the incorrect identification of the flow regimes is the small tube flow regime transition model in RELAP5 and the combined bubbly-slug flow regime in TRACE. We found that calculation results are sensitive to flow regime boundaries of RELAP5 which were modified in order to match the experimental data on flow regimes. Although the flow regime became closer to the experimental one, other predicted thermal hydraulic parameters showed larger discrepancy with the experimental data than with the base case calculations where flow regimes were misidentified.

scholarly journals CFD Modeling of Wall Steam Condensation: Two-Phase Flow Approach versus Homogeneous Flow Approach

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
S. Mimouni ◽  
N. Mechitoua ◽  
A. Foissac ◽  
M. Hassanaly ◽  
M. Ouraou
Keyword(s):  
Experimental Data ◽  
Liquid Film ◽  
Dominant Role ◽  
Droplet Diameter ◽  
Homogeneous Model ◽  
Surface Tension Force ◽  
Vapor Condensation ◽  
Cfd Modeling ◽  
Two Phase ◽  
Gravitational Forces

The present work is focused on the condensation heat transfer that plays a dominant role in many accident scenarios postulated to occur in the containment of nuclear reactors. The study compares a general multiphase approach implemented in NEPTUNE_CFD with a homogeneous model, of widespread use for engineering studies, implemented inCode_Saturne. The model implemented in NEPTUNE_CFD assumes that liquid droplets form along the wall within nucleation sites. Vapor condensation on droplets makes them grow. Once the droplet diameter reaches a critical value, gravitational forces compensate surface tension force and then droplets slide over the wall and form a liquid film. This approach allows taking into account simultaneously the mechanical drift between the droplet and the gas, the heat and mass transfer on droplets in the core of the flow and the condensation/evaporation phenomena on the walls. As concern the homogeneous approach, the motion of the liquid film due to the gravitational forces is neglected, as well as the volume occupied by the liquid. Both condensation models and compressible procedures are validated and compared to experimental data provided by the TOSQAN ISP47 experiment (IRSN Saclay). Computational results compare favorably with experimental data, particularly for the Helium and steam volume fractions.

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