Numerical Investigations of Centrifugal Compressor Flows With Tip Leakage Using a Pressure Correction Method

1993 ◽  
Author(s):  
A. Tourlidakis ◽  
R. L. Elder
Keyword(s):  
Flow Pattern ◽  
High Speed ◽  
Stokes Equations ◽  
Correction Method ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Physical Models ◽  
Wake Flow ◽  
Operating Characteristics ◽  
Pressure Correction

In this paper, a three-dimensional computational model for the solution of the time-averaged Navier-Stokes equations, based on a pressure correction method and the k-ε turbulence model, is presented and implemented for the viscous flow modelling through a series of centrifugal compressors. Theoretical calculations with the current fully elliptic method are carried out and the results are compared critically with available experimental data and with results from other computational models. A radial and two backswept high-speed subsonic compressors with different geometrical and operating characteristics are analysed at design and off-design conditions. In all cases, a wake flow pattern is evident and strong secondary flows are discerned. The tip clearance effects on the relative flow pattern are found to be important and are appropriately simulated. The predictive capability of the current flow model is judged to be encouraging taking into consideration the limitations of the physical models and the numerical schemes involved in the computations.

Quantitative Analysis of Reynolds and Navier–Stokes Based Modeling Approaches for Isothermal Newtonian Elastohydrodynamic Lubrication

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Leoluca Scurria ◽  
Tommaso Tamarozzi ◽  
Oleg Voronkov ◽  
Dieter Fauconnier
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Thickness Distribution ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Low Viscosity ◽  
Fluid Film Thickness

Abstract When simulating elastohydrodynamic lubrication, two main approaches are usually followed to predict the pressure and fluid film thickness distribution throughout the contact. The conventional approach relies on the Reynolds equation to describe the thin lubricant film, which is coupled to a Boussinesq description of the linear elastic deformation of the solids. A more accurate, yet a time-consuming method is the use of computational fluid dynamics in which the Navier–Stokes equations describe the flow of the thin lubricant film, coupled to a finite element solver for the description of the local contact deformation. This investigation aims at assessing both methods for different lubrication conditions in different elastohydrodynamic lubrication (EHL) regimes and quantify their differences to understand advantages and limitations of both methods. This investigation shows how the results from both approaches deviate for three scenarios: (1) inertial contributions (Re > 1), i.e., thick films, high speed, and low viscosity; (2) high shear stresses leading to secondary flows; and (3) large deformations of the solids leading to inaccuracies of the Boussinesq equation.

scholarly journals Modeling of Tip Clearance Flows Through an Improved 3-D Pressure Correction Navier-Stokes Solver

1993 ◽  
Author(s):  
N. Lymberopoulos ◽  
K. Giannakoglou ◽  
I. Nikolaou ◽  
K. D. Papailiou ◽  
A. Tourlidakis ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Special Treatment ◽  
Pressure Correction ◽  
Compressor Rotor ◽  
Numerical Predictions ◽  
Correction Technique

Mechanical constraints dictate the existence of tip clearances in rotating cascades, resulting to a flow leakage through this clearance which considerably influences the efficiency and range of operation of the machine. Three-dimensional Navier-Stokes solvers are often used for the numerical study of compressor and turbine stages with tip-clearance. The quality of numerical predictions depends strongly on how accurately the blade tip region is modelled; in this respect the accurate modelling of tip region was one of the main goals of this work. In the present paper, a 3-D Navier-Stokes solver is suitably adapted so that the flat tip surface of a blade and its sharp edges could be accurately modelled, in order to improve the precision of the calculation in the tip region. The adapted code solves the fully elliptic, steady, Navier-Stokes equations through a space-marching algorithm and a pressure correction technique; the H-type topology is retained, even in cases with thick leading edges where a special treatment is introduced herein. The analysis is applied to two different cases, a linear cascade and a compressor rotor, and comparisons with experimental data are provided.

Velocity characteristics in a multiphase pump under different tip clearances

2020 ◽  
pp. 095765092094653
Author(s):  
Guangtai Shi ◽  
Zongku Liu ◽  
Yexiang Xiao ◽  
Helin Li ◽  
Xiaobing Liu
Keyword(s):  
Velocity Distribution ◽  
Flow Rate ◽  
High Speed ◽  
Stokes Equations ◽  
Design Flow ◽  
Tip Clearance ◽  
High Speed Photography ◽  
Hydraulic Loss ◽  
Impeller Blade ◽  
Multiphase Pump

To investigate the effect of tip clearance on the velocity distribution in a multiphase pump, the internal flow and velocity distribution characteristics in pump under different tip clearances are studied using experimental and numerical methods. Simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS) and the standard k-ε turbulence model are carried out using ANSYS CFX. Under conditions of inlet gas void fraction (IGVF) is 5% at the flow rate of 0.6Q, 0.7Q and 0.8Q (Q is the design flow rate), the accuracy of the numerical method is verified by comparing with the experimental data using high-speed photography. Results show that the leakage flow interacts with the main flow and evolves into the tip leakage vortex (TLV). Due to the TLV, the pressure, velocity, turbulent kinetic energy (TKE), vorticity and streamlines on the S2 stream surface in the impeller and diffuser are changed greatly under different tip clearances. The velocities at the impeller outlet and diffuser inlet along the radial direction are also changed. The axial velocity distribution is similar to the meridional velocity distribution at the impeller blade outlet. While the relative velocity and absolute velocity distribution show the opposite trends. In addition, the vorticity is larger near the tip separated vortex and the hydraulic loss in pump is also increased due to the TLV.

Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor

1999 ◽  
Vol 121 (4) ◽  
pp. 751-762 ◽  
Author(s):  
G. A. Gerolymos ◽  
I. Vallet
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Main Flow ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Computational Method ◽  
Tip Vortex ◽  
Computational Results ◽  
Transonic Compressor ◽  
Compressor Rotor

The purpose of this paper is to investigate tip-clearance and secondary flows numerically in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged three-dimensional compressible Navier–Stokes equations, using the Launder–Sharma near-wall k–ε turbulence closure. In order to describe the flowfield through the tip and its interaction with the main flow accurately, a fine O-grid is used to discretize the tip-clearance gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jetlike flow through the gap and the main flow. An H–O–H grid is used for the computation of the main flow. In order to substantiate the validity of the results, comparisons with experimental measurements are presented for the NASA_37 rotor near peak efficiency using three grids (of 106, 2 X 106, and 3 X 106 points, with 21, 31, and 41 radial stations within the gap, respectively). The Launder–Sharma k–ε model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap, and the mixing downstream of the rotor. The computational results indicate the presence of an important leakage-interaction region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge tip vortex is also clearly visible.

scholarly journals A New Endwall Model for Axial Compressor Throughflow Calculations

1994 ◽  
Author(s):  
John Dunham
Keyword(s):  
High Speed ◽  
Axial Compressor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Major Influence ◽  
Complex Flow ◽  
Flow Angle ◽  
Empirical Estimates ◽  
Wall Boundary Layer ◽  
Surge Margin

It is well recognised that the endwall regions of a compressor — in which the annulus wall flow interacts with the mainstream flow — have a major influence on its efficiency and surge margin. Despite many attempts over the years to predict the very complex flow patterns in the endwall regions, current compressor design methods still rely largely on empirical estimates of the aerodynamic losses and flow angle deviations in these regions. This paper describes a new phenomenological model of the key endwall flow phenomena treated in a circumferentially-averaged way. It starts from Hirsch and de Ruyck’s annulus wall boundary layer approach, but makes some important changes. The secondary vorticities arising from passage secondary flows and from tip clearance flows are calculated. Then the radial interchanges of momentum, energy and entropy arising from both diffusion and convection are estimated The model is incorporated into a streamline curvature program. The empirical blade force defect terms in the boundary layers are selected from cascade data. The effectiveness of the method is illustrated by comparing the predictions with experimental results on both low speed and high speed multistage compressors. It is found that the radial variation of flow parameters is quite well predicted, and so is the overall performance, except when significant endwall stall occurs.

Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor

1998 ◽  
Author(s):  
G. A. Gerolymos ◽  
I. Vallet
Keyword(s):  
Stokes Equations ◽  
Mixing Layer ◽  
Main Flow ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Computational Method ◽  
Tip Vortex ◽  
Computational Results ◽  
Transonic Compressor ◽  
Compressor Rotor

The purpose of this paper is to numerically investigate tip-clearance and secondary flows in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged 3-D compressible Navier-Stokes equations, using the Launder-Sharma near-wall k-ε turbulence closure. In order to accurately describe the flowfield through the tip and its interaction with the main flow, a fine O-grid is used to discretize the tip-clearance-gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jet-like flow through the gap and the main flow. An H-O-H grid is used for the computation of the main flow. In order to substantiate the validity of the results comparisons with experimental measurements are presented for the NASA_37 rotor near peak efficiency using 3 grids (of 106, 2 × 106, and 3 × 106 points, with 21, 31, and 41 radial stations within the gap respectively). The Launder-Sharma k-ε model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap and the mixing downstream of the rotor. The computational results indicate the presence of an important leakage-interaction-region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge-tip-vortex is also clearly visible.

scholarly journals Secondary Flows and Vortex Motion in a High-Efficiency Backswept Impeller at Design and Off-Design Conditions

1989 ◽  
Author(s):  
C. Hah ◽  
H. Krain
Keyword(s):  
Flow Pattern ◽  
High Efficiency ◽  
Pressure Ratio ◽  
Vortex Motion ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Optimum Shape ◽  
Discharge Velocity ◽  
Type Flow

The 3-D viscous flowfield of a 4.7:1 pressure ratio backswept impeller was studied experimentally and numerically by using laser velocimetry and an advanced 3-D viscous code. The impeller was designed by a CAD method, and a maximum rotor efficiency of 94% was achieved. Both the experimental and the theoretical approach revealed comparatively smooth impeller discharge velocity profiles at all three operating conditions (design, choke, and near surge) differing widely from the well-known jet/wake type flow pattern. The 3-D viscous code was used for detailed flowfield studies, i.e., secondary flows; vortex motion and tip-clearance effects were analyzed at design and off-design conditions. The comparison of experimental and numerical results indicates that the tip-clearance effect should be properly modeled to predict the impeller flow pattern properly and that optimum shape of rotor exit flow pattern can be obtained by controlling the swirling vortex motion.

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