High Reynolds Number, Unsteady, Multiphase CFD Modeling of Cavitating Flows

2002 ◽  
Vol 124 (3) ◽  
pp. 607-616 ◽  
Author(s):  
Jules W. Lindau ◽  
Robert F. Kunz ◽  
David A. Boger ◽  
David R. Stinebring ◽  
Howard J. Gibeling
Keyword(s):  
Density Ratio ◽  
Three Dimensional ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Cavitating Flows ◽  
Good Convergence ◽  
Noncondensable Gas ◽  
Flow Features ◽  
Unsteady Rans ◽  
High Reynolds

A preconditioned, homogeneous, multiphase, Reynolds Averaged Navier-Stokes model with mass transfer is presented. The model is preconditioned in order to obtain good convergence and accuracy regardless of phasic density ratio or flow velocity. Engineering relevant validative unsteady two and three-dimensional results are given. A demonstrative three-dimensional, three-field (liquid, vapor, noncondensable gas) transient is also presented. In modeling axisymmetric cavitators at zero angle-of-attack with 3-D unsteady RANS, significant asymmetric flow features are obtained. In comparison with axisymmetric unsteady RANS, capture of these features leads to improved agreement with experimental data.

How Turbulence Models Perform in Simulating Pipeflow Response to Targeted Wall-Shapes?

2021 ◽  
Author(s):  
Mehran Masoumifar ◽  
Suyash Verma ◽  
Arman Hemmati
Keyword(s):  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Flow Response ◽  
High Reynolds Numbers ◽  
Flow Features ◽  
Rans Models ◽  
Response And Recovery ◽  
High Reynolds

Abstract This study evaluates how Reynolds-Averaged-Navier-Stokes (RANS) models perform in simulating the characteristics of mean three-dimensional perturbed flows in pipes with targeted wall-shapes. Capturing such flow features using turbulence models is still challenging at high Reynolds numbers. The principal objective of this investigation is to evaluate which of the well-established RANS models can best predict the flow response and recovery characteristics in perturbed pipes at moderate and high Reynolds numbers (10000-158000). First, the flow profiles at various axial locations are compared between simulations and experiments. This is followed by assessing the well-known mean pipeflow scaling relations. The good agreement between our computationally predicted data using Standard k-epsilon model and those of experiments indicated that this model can accurately capture the pipeflow characteristics in response to introduced perturbation with smooth sinusoidal axial variations.

scholarly journals Numerical Calculations of a Turbine Volute Using a 3-D Navier-Stokes Solver

1996 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
K. R. Pullen ◽  
F. Shi
Keyword(s):  
Three Dimensional ◽  
Circular Cross Section ◽  
Staggered Grid ◽  
Navier Stokes ◽  
Complex Flow ◽  
Numerical Predictions ◽  
Flow Features ◽  
Simplec Algorithm ◽  
Complicated Geometry ◽  
High Reynolds

The turbine volute is a complex flow device, about which a few papers on both measurements and CFD predictions have appeared. The main reasons for the difficulties being the complicated geometry which hinders measurements to be taken by both intrusive and non-intrusive techniques, and makes the numerical predictions difficult. In this paper, the complex three-dimensional flow through a turbine volute with non-symmetric circular cross-section is studied by using a 3-D Navier-Stokes solver which has been developed by the authors. In this solver, the fully 3-D Reynolds averaged N-S equations coupled with high Reynolds number k-ε turbulence model together with the wall function under arbitrary curvilinear coordinate system are solved. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLEC algorithm) with the non-staggered grid arrangement is used. In order to eliminate the decoupling between the velocity and pressure under non-staggered grid system, the physical covariant velocity component is selected as dependent variable in momentum equations and a momentum interpolation approach is employed. The validity of the free-vortex assumption is reviewed. The computation results are compared with a set of experiments performed previously by one of the authors. The flow features in the volute are discussed.

The three-dimensional structure of confined swirling flows with vortex breakdown

2001 ◽  
Vol 426 ◽  
pp. 155-175 ◽  
Author(s):  
FOTIS SOTIROPOULOS ◽  
YIANNIS VENTIKOS
Keyword(s):  
Stokes Equations ◽  
Vortex Breakdown ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Dimensional Structure ◽  
Navier Stokes ◽  
Recent Experimental Study ◽  
Flow Features ◽  
Stationary Vortex ◽  
High Reynolds

In a recent experimental study, Spohn, Mory & Hopfinger (1998) investigated in detail the flow in a closed cylindrical container with a rotating bottom for Reynolds numbers in the steady and unsteady regimes. Their visualization photographs revealed that the stationary vortex breakdown bubbles, which form along the container axis within a range of governing parameters, are open, with inflow and outflow, and asymmetric at their downstream end. For Reynolds numbers within the unsteady regime, visualizations of the limiting streamlines on the cylindrical wall showed that the Stewartson layer separates asymmetrically along stationary spiral convergence lines that form below the top cover. We study numerically the container flow, by solving the unsteady, three-dimensional Navier–Stokes equations, in order to clarify the origin and elucidate the underlying physics of these complex, three-dimensional flow features. The stationary vortex breakdown bubbles we simulate exhibit all the asymmetries observed in the laboratory. By analysing the Lagrangian characteristics of the calculated flow fields, we explain the origin of these asymmetries, clarify the experimentally documented filling and emptying mechanisms, and show that the flow in the interior of stationary vortex breakdown bubbles exhibits chaotic particle paths. We also show that the spiral separation lines observed by Spohn et al. (1998) inside the Stewartson layer at high Reynolds numbers are due to the growth of pairs of counter-rotating, spiral vortices and the interaction of these vortices with the stationary-cover boundary layer.

Vortex Suppression Efficiency of Discontinuous Helicoidal Fins

2007 ◽  
Author(s):  
Antonio Pinto ◽  
Riccardo Broglia ◽  
Elena Ciappi ◽  
Andrea Di Mascio ◽  
Emilio F. Campana ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Computational Time ◽  
Reynolds Number Flow ◽  
Flow Past A Cylinder ◽  
Helical Strakes ◽  
Unsteady Rans ◽  
Number Flow ◽  
Offshore Industry ◽  
Good Trade ◽  
High Reynolds

Vortex-Induced Vibration (VIV) is one of the most demanding areas in the offshore industry, and detailed investigation of the fluid-structure interaction is becoming fundamental for designing new structures able to reduce VIV phenomenon. To carry on such analysis, and get reliable results in term of global coefficients, the correct modelling of turbulence, boundary layer, and separated flows is required. Nonetheless, the more accurate is the simulation, the more costly is the computation. Unsteady RANS simulations provide a good trade-off between numerical accuracy and computational time. This paper presents the analysis of the flow past a cylinder with several three-dimensional helical fins at high Reynolds number. Flow field, vortical structures, and response frequency patterns are analysed. Spectral analysis of data is performed to identify carrier frequencies, deemed to be critical due to the induced vibration of the whole structure. Finally, helical strakes efficiency in reducing the riser vibrations is also addressed, through direct consideration on the carrier shedding frequency.

Three-Dimensional/One-Dimensional Combined Simulation of Deep Surge Loop in a Turbocharger Compressor With Vaned Diffuser

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ghislaine Ngo Boum ◽  
Rodolfo Bontempo ◽  
Isabelle Trébinjac
Keyword(s):  
System Modeling ◽  
Air Flow ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vaned Diffuser ◽  
One Dimensional ◽  
Compressor Surge ◽  
Important Challenge ◽  
Unsteady Rans ◽  
Combined Simulation

High accuracy simulation of compressor surge origin and growth is an important challenge for designers of systems using compressors likely to develop that severe instability. Indeed, understanding its driving phenomena, which can be system dependent, is necessary to build an adequate strategy to avoid or control surge emergence. Computational fluid dynamics (CFD) simulations, commonly used to explore flow in the compressor, need then to be extended beyond the compressor as surge is a system scale instability. To get an insight on the path to surge and through surge cycles, a reliable alternative to full three-dimensional (3D) system modeling is used for a turbocharger compressor inserted in an experimental test rig. The air flow in the whole circuit, is modeled with a one-dimensional (1D) Navier Stokes approach which is coupled with a 3D unsteady RANS modeling of the 360 deg air flow in the centrifugal compressor including the volute. Starting from an initial stable flow solution in the system, the back-pressure valve is progressively closed to reduce the massflow and trigger the instability. An entire deep surge loop is simulated and compared with good agreement with the experimental data. The existence of a system-induced convective wave is revealed, and its major role on surge inception at diffuser inlet demonstrated.

scholarly journals Numerical Study of the Internal Flow Field of a Centrifugal Impeller

1994 ◽  
Author(s):  
Mou-jin Zhang ◽  
Chuan-gang Gu ◽  
Yong-miao Miao
Keyword(s):  
Flow Field ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Simple Algorithm ◽  
Internal Flow ◽  
Staggered Grid ◽  
Navier Stokes ◽  
Centrifugal Impeller ◽  
High Reynolds

The complex three-dimensional flow field in a centrifugal impeller with low speed is studied in this paper. Coupled with high–Reynolds–number k–ε turbulence model, the fully three–dimensional Reynolds averaged Navier–Stokes equations are solved. The Semi–Implicit Method for Pressure–Linked Equations (SIMPLE) algorithm is used. And the non–staggered grid arrangement is also used. The computed results are compared with the available experimental data. The comparison shows good agreement.

Some Aspects of CFD Modeling in the Analysis of a Low-Pressure Steam Turbine

2007 ◽  
Author(s):  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Stefano Cecchi ◽  
Federico Dacca`
Keyword(s):  
Steam Turbine ◽  
Computational Cost ◽  
Three Dimensional ◽  
Low Pressure ◽  
Design Tool ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Sources And Sinks ◽  
Leakage Flows ◽  
Pressure Steam

A three-dimensional, multistage, Navier-Stokes solver is applied to the numerical investigation of a four stage low-pressure steam turbine. The thermodynamic behavior of the wet steam is reproduced by adopting a real-gas model, based on the use of gas property tables. Geometrical features and flow-path details consistent with the actual turbine geometry, such as cavity purge flows, shroud leakage flows and partspan snubbers, are accounted for, and their impact on the turbine performance is discussed. These details are included in the analysis using simple models, which prevent a considerable growth of the computational cost and make the overall procedure attractive as a design tool for industrial purposes. Shroud leakage flows are modeled by means of suitable endwall boundary conditions, based on coupled sources and sinks, while body forces are applied to simulate the presence of the damping wires on the blades. In this work a detailed description of these models is provided, and the results of computations are compared with experimental measurements.

Unsteady RANS Simulation of Turbulent Flow and Heat Transfer in Ribbed Coolant Passages of Different Aspect Ratios

2004 ◽  
Author(s):  
A. K. Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Rotation Number ◽  
Large Scale ◽  
Density Ratio ◽  
Navier Stokes ◽  
Flow Structures ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Unsteady Rans

The flow and heat transfer in ribbed coolant passages of aspect ratios (AR) of 1:1, 4:1, and 1:4 are numerically studied through the solution of the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. The ribs are oriented normal to the flow and arranged in a staggered configuration on the leading and trailing surfaces. The URANS procedure can resolve large-scale bulk unsteadiness, and utilizes a two equation k-ε model for the turbulent stresses. Both Coriolis and centrifugal buoyancy effects are included in the simulations. The computations are carried out for a fixed Reynolds number of 25000 and density ratio of 0.13 while the Rotation number has been varied between 0.12–0.50. The average duct heat transfer is the highest for the 4:1 AR case. For this case, the secondary flow structures consist of multiple roll cells that direct flow both to the trailing and leading surfaces. The 1:4 AR duct shows flow reversal along the leading surface at high rotation numbers with multiple rolls in the secondary flow structures near the leading wall. For this AR, the potential for conduction-limited heat transfer along the leading surface is identified. At high rotation number, both the 1:1 and 4:1 AR cases exhibit loss of axial periodicity over one inter-rib module. The friction factor reveals an increase with the rotation number for all aspect ratio ducts, and shows a sudden jump in its value at a critical rotation number because of either loss of spatial periodicity or the onset of backflow.

An Assessment of Turbulence Models for Predicting the Fluid Flow in Spiral Casing of a Hydraulic Turbomachine Using SUPG-Finite Element Method

2013 ◽  
Author(s):  
N. Parameswara Rao ◽  
K. Arul Prakash
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Spatial Discretisation ◽  
High Reynolds ◽  
Spiral Casing ◽  
Element Method

Numerical simulation of complex three-dimensional flow through the spiral casing has been studied using a finite element method. An explicit Eulerian velocity correction scheme has been employed to solve the Reynolds averaged Navier-stokes equations. The simulation has been performed to describe the flow in high Reynolds number (106) regime and two k-ε turbulence models (standard k-ε and RNG k-ε) have been used for computing the turbulent flow. A streamline upwind Petrov Galerkin technique has been used for spatial discretisation. The velocity field and the pressure distribution inside the spiral casing has been studied. It has been observed that very strong secondary flow is evolved on the cross-stream planes.

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