Numerical Study of Deterministic Fluxes in Compressor Passages

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Feng Wang ◽  
Mauro Carnevale ◽  
Luca di Mare
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Navier Stokes ◽  
Design Stage ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Radial Profiles ◽  
And Performance ◽  
Stage Matching ◽  
Unsteady Effects

Computational fluid dynamics (CFD) has been widely adopted in the compressor design process, but it remains a challenge to predict the flow details, performance, and stage matching for multistage, high-speed machines accurately. The Reynolds Averaged Navier-Stokes (RANS) simulation with mixing plane for bladerow coupling is still the workhorse in the industry and the unsteady bladerow interaction is discarded. This paper examines these discarded unsteady effects via deterministic fluxes using semi-analytical and unsteady RANS (URANS) calculations. The study starts from a planar duct under periodic perturbations. The study shows that under large perturbations, the mixing plane produces dubious values of flow quantities (e.g., whirl angle). The performance of the mixing plane can be considerably improved by including deterministic fluxes into the mixing plane formulation. This demonstrates the effect of deterministic fluxes at the bladerow interface. Furthermore, the front stages of a 19-blade row compressor are investigated and URANS solutions are compared with RANS mixing plane solutions. The magnitudes of divergence of Reynolds stresses (RS) and deterministic stresses (DS) are compared. The effect of deterministic fluxes is demonstrated on whirl angle and radial profiles of total pressure and so on. The enhanced spanwise mixing due to deterministic fluxes is also observed. The effect of deterministic fluxes is confirmed via the nonlinear harmonic (NLH) method which includes the deterministic fluxes in the mean flow, and the study of multistage compressor shows that unsteady effects, which are quantified by deterministic fluxes, are indispensable to have credible predictions of the flow details and performance of compressor even at its design stage.

Numerical Study of Deterministic Fluxes in Compressor Passages

2018 ◽  
Author(s):  
Feng Wang ◽  
Mauro Carnevale ◽  
Luca di Mare
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Navier Stokes ◽  
Design Stage ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Multi Stage ◽  
Radial Profiles ◽  
Stage Matching ◽  
Unsteady Effects

Computational Fluid Dynamics (CFD) has been widely adopted at the compressor design process, but it remains a challenge to predict the flow details, performance and stage matching for multi-stage, high-speed machines accurately. The Reynolds Averaged Navier-Stokes (RANS) simulation with mixing plane for bladerow coupling is still the workhorse in the industry and the unsteady bladerow interaction is discarded. This paper examines these discarded unsteady effects via deterministic fluxes using semi-analytical and URANS calculations. The study starts from a planar duct under periodic perturbations. The study shows that under large perturbations, the mixing plane produces dubious mixed-out variables, e.g. whirl angle. The performance of the mixing plane can be considerably improved by including deterministic fluxes into the mixing plane formulation. This demonstrates the effect of deterministic fluxes at the bladerow interface. Furthermore the front stages of a 19-blade row compressor are investigated and URANS solutions are compared with RANS solutions. The magnitude of divergence of Reynolds stresses and deterministic stresses are compared. The effect of deterministic fluxes are demonstrated on whirl angle and radial profiles of total pressure and so on. The enhanced spanwise mixing due to deterministic fluxes are also observed. The effect of deterministic fluxes are confirmed via the non-linear harmonic method which includes the deterministic fluxes in the mean flow and the study of multistage compressor shows that unsteady effects, which are quantified by deterministic fluxes, are indispensable to have credible predictions of the flow details and performance of compressor even at its design stage.

scholarly journals Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing

2019 ◽  
Vol 475 (2225) ◽  
pp. 20190018
Author(s):  
E. Yim ◽  
P. Meliga ◽  
F. Gallaire
Keyword(s):  
Turbulent Flow ◽  
Finite Amplitude ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Backward Facing Step ◽  
Eddy Viscosity Model ◽  
Coherent Interaction ◽  
Self Consistent ◽  
The Mean

We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent–incoherent interaction is lumped into a Reynolds averaged Navier–Stokes (RANS) eddy viscosity model, and the mean–coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantič-Lugo & Gallaire (2016 J. Fluid Mech. 793 , 777–797. ( doi:10.1017/jfm.2016.109 )). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.

Investigation of the Flow Structures in Supersonic Free and Impinging Jet Flows

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
C. Chin ◽  
M. Li ◽  
C. Harkin ◽  
T. Rochwerger ◽  
L. Chan ◽  
...  
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Experimental Studies ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Optical Methods ◽  
Navier Stokes ◽  
Jet Flows ◽  
Shock Cell ◽  
Rans Turbulence Models

A numerical study of compressible jet flows is carried out using Reynolds averaged Navier–Stokes (RANS) turbulence models such as k-ɛ and k-ω-SST. An experimental investigation is performed concurrently using high-speed optical methods such as Schlieren photography and shadowgraphy. Numerical and experimental studies are carried out for the compressible impinging at various impinging angles and nozzle-to-wall distances. The results from both investigations converge remarkably well and agree with experimental data from the open literature. From the flow visualizations of the velocity fields, the RANS simulations accurately model the shock structures within the core jet region. The first shock cell is found to be constraint due to the interaction with the bow-shock structure for nozzle-to-wall distance less than 1.5 nozzle diameter. The results from the current study show that the RANS models utilized are suitable to simulate compressible free jets and impinging jet flows with varying impinging angles.

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.

Numerical Study of Air Gap Response and Wave Impact Load on a Moored Semi-Submersible Platform in Predetermined Irregular Wave Train

2010 ◽  
Author(s):  
Xiufeng Liang ◽  
Jianmin Yang ◽  
Longfei Xiao ◽  
Xin Li ◽  
Jun Li
Keyword(s):  
Impact Load ◽  
Numerical Study ◽  
Wave Train ◽  
Air Gap ◽  
Navier Stokes ◽  
Design Stage ◽  
Wave Impact ◽  
Irregular Wave ◽  
Run Up ◽  
Steep Waves

The importance of understanding air gap response and potential deck impact is well-known in the design stage of semi-submersible platform. The highly non-linear nature of wave elevation around large structures in steep waves makes it difficult to accurately predict wave field under the deck and wave run up along the columns. Present engineering tools for the prediction of air gap response generally based on simplified models. Even the models accounting for nonlinear wave diffraction is not free of uncertainties. A method adopted here couples a Navier-Stokes solver, VOF technique capturing violent free surface and DNV/Seasam predicting motions of moored semi-submersible platform. Air gap response at different locations of the hull was evaluated in predetermined irregular wave train. Wave run up was also measured by wave probes near the columns. Load cells were mounted under the deck of the platform to trace potential deck impact. The predetermined irregular wave train was simulated in a numerical wave tank and verified against physical tank results. Analysis of the air gap response, wave run up and impact loads on the semi-submersible platform were conducted.

scholarly journals RIP CURRENTS ON A BARRED BEACH

2012 ◽  
Vol 1 (33) ◽  
pp. 38
Author(s):  
Andrea Ruju ◽  
Pablo Higuera ◽  
Javier L. Lara ◽  
Inigo J. Losada ◽  
Giovanni Coco
Keyword(s):  
Boundary Conditions ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Wave Generation ◽  
Dimensional Structure ◽  
Navier Stokes ◽  
Rip Currents ◽  
Mean Flow ◽  
Forcing Mechanisms

This work presents the numerical study of rip current circulation on a barred beach. The numerical simulations have been carried out with the IH-FOAM model which is based on the three dimensional Reynolds Averaged Navier-Stokes equations. The new boundary conditions implemented in IH-FOAM have been used, including three dimensional wave generation as well as active wave absorption at the boundary. Applying the specific wave generation boundary conditions, the model is validated to simulate rip circulation on a barred beach. Moreover, this study addresses the identification of the forcing mechanisms and the three dimensional structure of the mean flow.

A Numerical Study of Vortex Breakdown in Turbulent Swirling Flows

1999 ◽  
Vol 122 (1) ◽  
pp. 179-183 ◽  
Author(s):  
Robert E. Spall ◽  
Blake M. Ashby
Keyword(s):  
Reynolds Stress ◽  
Stokes Equations ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Stress Model ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
The Mean

Solutions to the incompressible Reynolds-averaged Navier–Stokes equations have been obtained for turbulent vortex breakdown within a slightly diverging tube. Inlet boundary conditions were derived from available experimental data for the mean flow and turbulence kinetic energy. The performance of both two-equation and full differential Reynolds stress models was evaluated. Axisymmetric results revealed that the initiation of vortex breakdown was reasonably well predicted by the differential Reynolds stress model. However, the standard K-ε model failed to predict the occurrence of breakdown. The differential Reynolds stress model also predicted satisfactorily the mean azimuthal and axial velocity profiles downstream of the breakdown, whereas results using the K-ε model were unsatisfactory. [S0098-2202(00)01601-1]

Validation of Particle-Laden Turbulent Flow Simulations Including Turbulence Modulation

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Yvonne Reinhardt ◽  
Leonhard Kleiser
Keyword(s):  
Numerical Study ◽  
Density Ratio ◽  
Particle Diameter ◽  
Stokes Number ◽  
Navier Stokes ◽  
Mean Flow ◽  
Turbulent Length Scale ◽  
Turbulence Modulation ◽  
Flow Simulations ◽  
Wide Range

The objective of the present numerical study is the validation of wall-bounded, turbulent particle-laden air flow simulations for a wide range of flow and particle parameters (i.e., flow and particle Reynolds numbers, Stokes number, particle-to-fluid density ratio, ratio of particle diameter to turbulent length scale) covering the one-, two- and four-way coupling regimes. The applied computational fluid dynamics (CFD) model follows the Eulerian two-fluid approach in a Reynolds-Averaged Navier–Stokes (RANS) context and is based on the kinetic theory of granular flow (KTGF) for closures concerning the particulate phase. The fluid turbulence is modeled applying a low-Reynolds-number k–epsilon turbulence model. The main focus is put on the modeling of turbulence coupling between the fluid and the particle phase. Different from common practice, the choice of a model accounting for turbulence modulation is made dependent on the prevailing coupling regime. For the case of four-way coupling, a new modulation model is suggested that well predicts turbulence augmentation and attenuation. The predictive capabilities of the present approach are evaluated by comparing simulation results to experimental benchmark data of various pipe and channel flows. Very good agreement with reference data is obtained for the mean flow and turbulence profiles of both phases.

Experimental and Numerical Investigation on Windage Power Losses in High Speed Gears

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Daniele Massini ◽  
Tommaso Fondelli ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
Lorenzo Tarchi ◽  
...  
Keyword(s):  
High Speed ◽  
Spur Gear ◽  
Relative Magnitude ◽  
Navier Stokes ◽  
Power Losses ◽  
Test Rig ◽  
Viscosity Models ◽  
Image Velocimetry ◽  
And Performance ◽  
Aero Engines

Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. An evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Mechanical power losses are usually distinguished into two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid dynamics of the environment, which surrounds the gears. The relative magnitude of these phenomena is dependent on the operative conditions of the transmission: load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. A new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry (PIV) measurements for investigating the flow field surrounding the rotating gear. The experiment has been computationally replicated, performing Reynolds-averaged Navier–Stokes (RANS) simulations in the context of conventional eddy viscosity models, achieving good agreement for all of the speed of rotations.

scholarly journals Effect of Rotor–Stator Interaction on Impeller Performance in Centrifugal Compressors

1999 ◽  
Vol 5 (2) ◽  
pp. 135-146 ◽  
Author(s):  
K. Sato ◽  
L. He
Keyword(s):  
Navier Stokes ◽  
Test Case ◽  
Steady Flows ◽  
Centrifugal Compressors ◽  
Vaned Diffuser ◽  
Rotor Stator Interaction ◽  
Flow Through ◽  
And Performance ◽  
Unsteady Effects ◽  
Blade Row Interaction

A 3-D unsteady thin-layer Navier-Stokes code has been used to calculate the flow through a centrifugal compressor stage. The validation of the code for steady flows in centrifugal compressors was conducted for the Krain’s impeller with a vaneless diffuser as a test case and the numerical results were compared with the experimental results. The predicted flow field and performance agreed well with the experimental data. An unsteady stage solution was then conducted with this impeller followed by a generic low-solidity vaned-diffuser to examine the unsteady effects on the impeller performance. The computational results showed a stabilising effect of the blade row interaction.

Sign in / Sign up

Export Citation Format

Share Document