Computational Analysis of Scroll Tongue Shapes to Compressor Performance by Using Different Turbulence Models

2007 ◽  
Author(s):  
Cheng Xu ◽  
R. S. Amano
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Equation Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Operating Range ◽  
Performance Predictions ◽  
Compressor Performance ◽  
Compressor Efficiency

A scroll is used to collect and transport swirling fluid produced by impeller or diffuser. Scroll or volute is one of the key components of centrifugal compressors. Design of the scroll not only impacts compressor efficiency but also influences operating range of the compressor. In this study, navier-stokes equations combined with both an zero-equation turbulence model and the k-ε turbulence model were used to simulate the flows inside a single stage compressor. Detailed flow simulations for a large cut back tongue scroll were presented and discussed. Studies showed that a large cut back rounded tongue scroll provided good operating range without dropping compressor peak efficiency dramatically. The turbulence model influences to the calculation were discussed and some suggestions for scroll flow modeling were made. The numerical results obtained using two turbulence models were compared and showed agreement reasonably well with experiments. Although the k-ε model behaves well inside the boundary layer, it was not decisively better than the zero-equation model for the performance predictions.

Analyses of Centrifugal Compressor Performance Impacts on Volute and Scroll

2010 ◽  
Author(s):  
C. Xu ◽  
R. S. Amano
Keyword(s):  
Static Pressure ◽  
Stokes Equations ◽  
Single Stage ◽  
Navier Stokes ◽  
Performance Tests ◽  
Peak Efficiency ◽  
Navier Stokes Equations ◽  
Flow Simulations ◽  
Compressor Performance ◽  
Compressor Efficiency

Volute is used to collect and transport swirling gas produced by impeller or diffuser. Design of the volute not only impacts compressor efficiency but also influences the operating ranges of the compressor. In this study, Navier-Stokes equations combined with an algebra turbulence model were used to simulate flows inside a single stage compressor. Detailed flow simulations for a large cut back tongue volute are presented and discussed. A rounded tongue volute was tested in a single stage test rig. The compressor stage performance tests were conducted in the test lab and static pressure taps were used to measure static pressures at volute internal walls at locations of θ = 240° and 360°. Thermal couples and other static pressure probes were instrumented at inlet and outlet of the compressor for performance tests. The numerical results were compared with experiments and good agreements are found. Studies showed that a large cut back rounded tongue volute provided good operating range without dramatically dropping compressor peak efficiency.

Reynolds-Averaged Navier–Stokes Equations for Turbulence Modeling

2009 ◽  
Vol 62 (4) ◽  
Author(s):  
Giancarlo Alfonsi
Keyword(s):  
Turbulent Flows ◽  
Incompressible Flows ◽  
Stokes Equations ◽  
Nonlinear Models ◽  
Turbulence Models ◽  
Equation Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Linear And Nonlinear ◽  
Reynolds Averaged Navier Stokes

The approach of Reynolds-averaged Navier–Stokes equations (RANS) for the modeling of turbulent flows is reviewed. The subject is mainly considered in the limit of incompressible flows with constant properties. After the introduction of the concept of Reynolds decomposition and averaging, different classes of RANS turbulence models are presented, and, in particular, zero-equation models, one-equation models (besides a half-equation model), two-equation models (with reference to the tensor representation used for a model, both linear and nonlinear models are considered), stress-equation models (with reference to the pressure-strain correlation, both linear and nonlinear models are considered) and algebraic-stress models. For each of the abovementioned class of models, the most widely-used modeling techniques and closures are reported. The unsteady RANS approach is also discussed and a section is devoted to hybrid RANS/large methods.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

Modeling of the Vortex-Structure in a Particle-Laden Mixing-Layer

2005 ◽  
Author(s):  
Jens A. Melheim ◽  
Stefan Horender ◽  
Martin Sommerfeld
Keyword(s):  
Vortex Structure ◽  
Stokes Equations ◽  
Fluid Velocity ◽  
Mixing Layer ◽  
Equation Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Calculated Concentration ◽  
Langevin Model ◽  
Particle Velocities

Numerical calculations of a particle-laden turbulent horizontal mixing-layer based on the Eulerian-Lagrangian approach are presented. Emphasis is given to the determination of the stochastic fluctuating fluid velocity seen by the particles in anisotropic turbulence. The stochastic process for the fluctuating velocity is a “Particle Langevin equation Model”, based on the Simplified Langevin Model. The Reynolds averaged Navier-Stokes equations are closed by the standard k-epsilon turbulence model. The calculated concentration profile and the mean, the root-mean-square (rms) and the cross-correlation terms of the particle velocities are compared with particle image velocimetry (PIV) measurements. The numerical results agree reasonably well with the PIV data for all of the mentioned quantities. The importance of the modeled vortex structure “seen” by the particles is discussed.

scholarly journals Off-Design Performance Prediction for Radial-Flow Impellers

1988 ◽  
Author(s):  
Shen C. Lee ◽  
Daying Chen
Keyword(s):  
Stokes Equations ◽  
Mechanical Energy ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Pump Impeller ◽  
Navier Stokes Equations ◽  
Measured Velocity ◽  
Production Water ◽  
Performance Predictions ◽  
Stream Functions

A numerical method was developed to consider the two-dimensional flowfield between impeller blades of a given geometry. Solution of the laminar Navier-Stokes equations in geometry-oriented coordinates was obtained for stream functions and vorticities. Velocities and pressures were calculated to determine the output fluid-energy head. The circumferential components of the normal and shear stresses along the blade were evaluated to give the input mechanical-energy head. Performance predictions were obtained for different load conditions. Comparisons were made with the measured velocity vectors of the flowfield of an air-pump impeller and with the measured performance of a production water pump, good agreements were reached.

scholarly journals Three-Dimensional Turbulent Vortex Shedding From a Surface-Mounted Square Cylinder: Predictions With Large-Eddy Simulations and URANS

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
B. A. Younis ◽  
A. Abrishamchi
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Large Eddy

The paper reports on the prediction of the turbulent flow field around a three-dimensional, surface mounted, square-sectioned cylinder at Reynolds numbers in the range 104–105. The effects of turbulence are accounted for in two different ways: by performing large-eddy simulations (LES) with a Smagorinsky model for the subgrid-scale motions and by solving the unsteady form of the Reynolds-averaged Navier–Stokes equations (URANS) together with a turbulence model to determine the resulting Reynolds stresses. The turbulence model used is a two-equation, eddy-viscosity closure that incorporates a term designed to account for the interactions between the organized mean-flow periodicity and the random turbulent motions. Comparisons with experimental data show that the two approaches yield results that are generally comparable and in good accord with the experimental data. The main conclusion of this work is that the URANS approach, which is considerably less demanding in terms of computer resources than LES, can reliably be used for the prediction of unsteady separated flows provided that the effects of organized mean-flow unsteadiness on the turbulence are properly accounted for in the turbulence model.

Turbulent Flow Velocity Between Rotating Co-Axial Disks of Finite Radius

1989 ◽  
Vol 111 (3) ◽  
pp. 333-340 ◽  
Author(s):  
J. F. Louis ◽  
A. Salhi
Keyword(s):  
Turbulent Flow ◽  
Turbulence Model ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Finite Radius ◽  
Navier Stokes Equations ◽  
Rotating Cavity ◽  
Tangential Wall ◽  
Frictional Forces

The turbulent flow between two rotating co-axial disks is driven by frictional forces. The prediction of the velocity field can be expected to be very sensitive to the turbulence model used to describe the viscosity close to the walls. Numerical solutions of the Navier–Stokes equations, using a k–ε turbulence model derived from Lam and Bremhorst, are presented and compared with experimental results obtained in two different configurations: a rotating cavity and the outflow between a rotating and stationary disk. The comparison shows good overall agreement with the experimental data and substantial improvements over the results of other analyses using the k–ε models. Based on this validation, the model is applied to the flow between counterrotating disks and it gives the dependence of the radial variation of the tangential wall shear stress on Rossby number.

A Numerical Study on Performances of Centrifugal Compressor Stages With Different Radial Gaps

2000 ◽  
Author(s):  
K. Sato ◽  
L. He
Keyword(s):  
Centrifugal Compressor ◽  
Stokes Equations ◽  
Numerical Study ◽  
Axial Compressor ◽  
Navier Stokes ◽  
Centrifugal Impeller ◽  
Vaned Diffuser ◽  
Navier Stokes Equations ◽  
Performance Predictions ◽  
Radial Gap

A numerical study of 3D unsteady flows in centrifugal compressor stages solving the Navier-Stokes equations is presented. The emphasis is on the effect of the radial gap between blade rows on the aerodynamic performance. In the numerical tests, Krain’s centrifugal impeller was combined with a DCA (Double Circular Arc) type radial vaned diffuser. The compressor stages with three settings of radial gap ranging from 5 to 15 percent of the impeller trailing edge radius are configured and unsteady flow simulations are carried out to compare the time-averaged efficiencies. The performance predictions show that the efficiency is deteriorated if the radial gap between blade rows is reduced with intensified blade row interaction, which is in contradiction to the general trend for axial compressor stages. In the centrifugal compressors tested, wake chopping by diffuser vanes, which usually benefits efficiency in axial compressor stages, causes unfavourable wake compression through the diffuser passages to deteriorate the efficiency.

A Reynolds-Averaged Navier-Stokes Solver in a Turbomachinery Design System

2007 ◽  
Author(s):  
Fahua Gu ◽  
Mark R. Anderson
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Integrated Design ◽  
Navier Stokes ◽  
Design System ◽  
Navier Stokes Equations ◽  
Wall Functions ◽  
Machine Performance ◽  
Reynolds Averaged Navier Stokes

The design of turbomachinery has been focusing on the improvement of the machine efficiency and the reduction of the design cost. This paper presents an integrated design system to create the machine geometry and to predict the machine performance at different levels of approximation, including one-dimensional design and analysis, quasi-three-dimensional-(blade-to-blade, throughflow) and full-three-dimensional-steady-state CFD analysis. One of the most important components, the Reynolds-averaged Navier-Stokes solver, is described in detail. It originated from the Dawes solver with numerous enhancements. They include the use of the low speed pre-conditioned full Navier-Stokes equations, the addition of the Spalart-Allmaras turbulence model and an improvement of wall functions related with the turbulence model. The latest upwind scheme, AUSM, has been implemented too. The Dawes code has been rewritten into a multi-block solver for O, C, and H grids. This paper provides some examples to evaluate the effect of grid topology on the machine performance prediction.

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