Chamber Dimension Effects on Induced Flow and Frictional Resistance of Enclosed Rotating Disks

1960 ◽  
Vol 82 (1) ◽  
pp. 217-230 ◽  
Author(s):  
J. W. Daily ◽  
R. E. Nece
Keyword(s):  
Boundary Layers ◽  
Turbulent Flows ◽  
Frictional Resistance ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Pressure Data ◽  
Rotating Disks ◽  
Disk Radius ◽  
Fluid Core ◽  
Axial Clearance

The fundamental fluid mechanics associated with the rotation of a smooth plane disk enclosed within a right-cylindrical chamber have been studied both experimentally and theoretically. In order to acquire further and systematic information pertinent to this problem, which has received much attention in the past, torque data were obtained over a range of disk Reynolds numbers from 103 to 107 for axial clearance-disk radius ratios s/a from 0.0127 to 0.217 for a constant small radial tip clearance and velocity and pressure data were obtained for laminar and turbulent flows. The existence of four basic flow regimes in the axial gap between the disk and casing wall was verified, and these regimes, the existence and extent of which are governed by the Reynolds number-axial spacing combinations, have been delineated. A new approximate theoretical analysis has accounted for axial-clearance effects for the case of separate boundary layers on the disk and end wall; this theory has been checked against test results. Velocity and pressure data have shown that the concept of a fluid “core” rotation in the case of separate boundary layers must be modified because of secondary flows and skewed boundary layers.

Roughness Effects on Frictional Resistance of Enclosed Rotating Disks

1960 ◽  
Vol 82 (3) ◽  
pp. 553-560 ◽  
Author(s):  
R. E. Nece ◽  
J. W. Daily
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Initial Point ◽  
Frictional Resistance ◽  
Reynolds Numbers ◽  
Tip Clearance ◽  
Rotating Disks ◽  
Roughness Effects ◽  
Disk Radius ◽  
Onset Of Turbulence

The effects of surface roughness on the frictional resistance of enclosed rotating disks have been studied experimentally. Torque data were obtained over the range of disk Reynolds numbers 4 × 103 to 6 × 106 for three different relative roughnesses a/k of 1000, 2000, and 3200 at three axial-clearance-to-disk-radius ratios s/a of 0.0227, 0.0609, and 0.112 for a constant, small, radial tip clearance. The existence of four possible basic flow regimes in the axial gap between the disk and casing wall was verified. Empirical expressions have been presented which predict the initial point of onset of turbulence in the flow within the boundary layer on the disk, the point at which the surface roughness becomes fully effective, and the magnitudes of the resistance coefficients in the zone of fully rough turbulent flow. The similarities and differences between smooth and rough-disk torque behavior, and to a limited extent boundary-layer behavior, have been noted.

scholarly journals Calculation of Turbulent Flows Through Linear Turbine Cascades With and Without Tip Clearance

1995 ◽  
Author(s):  
Hun G. Lee ◽  
Jung Y. Yoo ◽  
Jun W. Yun
Keyword(s):  
Turbulent Flows ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Group Method ◽  
Tip Clearance Flow ◽  
Vena Contracta

Three dimensional turbulent incompressible flows through linear cascades of turbine rotor blades with high turning angles have been analyzed numerically by using a generalized k-ε model which is a high Reynolds number form and derived by RNG (renormalized group) method to account for the variation of the rate of strain. A second order upwind scheme is used to suppress numerical diffusion in approximating the convective terms. Boundary-fitted coordinates are adopted to represent the complex blade geometry accurately. For the case without tip clearance, secondary flows and flow losses are shown to be in good agreement with previous experimental results. For the case with tip clearance, the effects of the passage vortex and tip clearance flow on the total pressure loss as well as their interactions are discussed. The flow within the tip clearance has been analyzed to illustrate the existences of the tip clearance vortex and vena contracta.

A New Approach to Predicting Annulus Wall Boundary Layers in Axial Compressors

1993 ◽  
Vol 207 (6) ◽  
pp. 413-425 ◽  
Author(s):  
J Dunham
Keyword(s):  
Boundary Layers ◽  
Phenomenological Approach ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Wall Effects ◽  
Axial Compressors ◽  
Wall Boundary ◽  
Empirical Scheme ◽  
Local Deviation ◽  
End Wall

This paper introduces a new phenomenological approach to modelling the end-wall effects. It is based on explicit calculations of the annulus wall boundary layers by Hirsch and de Ruyck's method, with significant changes to allow tip clearance effects to be represented, together with explicit calculations of the secondary flows outside the boundary layers using Marsh's equations. To achieve this, the secondary vorticity is computed throughout the compressor. A new simple model for the tip clearance vorticity is added. It is shown, by comparison with Salvage's cascade measurements and Inoue's isolated rotor measurements at varying tip clearance, that the method is capable of satisfactory predictions of the pitchwise-average local deviation and loss near the end-walls. The model is only accurate, however, when there is no significant end-wall flow separation. Two examples of complete multistage low-speed compressors are given. It is concluded that a promising foundation has been presented for a more satisfactory and more accurate way of predicting the end-wall effects than any published purely empirical scheme.

Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures

2010 ◽  
Author(s):  
Christian Eichler ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Turbulent Transport ◽  
Wall Friction ◽  
Evaluation Procedure ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Flame Flashback ◽  
Turbulent Wall

Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups have been investigated in the past and thus turbulent flashback limits were only derived for a fully-developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen and air at various mixing ratios. The associated wall friction distributions are determined by RANS computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared to literature values and the critical gradient concept is reviewed in light of the new data.

The Application of Non-Axisymmetric Endwall Contouring in a Single Stage, Rotating Turbine

2009 ◽  
Author(s):  
Glen Snedden ◽  
Dwain Dunn ◽  
Grant Ingram ◽  
David Gregory-Smith
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Full Scale ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Detailed Understanding ◽  
Low Speed ◽  
Endwall Contouring ◽  
Probe Measurements

As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.

Annulus Wall Boundary-Layer Measurements in a Four-Stage Compressor

1986 ◽  
Vol 108 (1) ◽  
pp. 2-6 ◽  
Author(s):  
N. A. Cumpsty
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Layer Thickness ◽  
Boundary Layers ◽  
Boundary Layer Thickness ◽  
Tip Clearance ◽  
The Other ◽  
Wall Boundary Layer ◽  
Multistage Compressors ◽  
Full Design

There are few available measurements of the boundary layers in multistage compressors when the repeating-stage condition is reached. These tests were performed in a small four-stage compressor; the flow was essentially incompressible and the Reynolds number based on blade chord was about 5 • 104. Two series of tests were performed; in one series the full design number of blades were installed, in the other series half the blades were removed to reduce the solidity and double the staggered spacing. Initially it was wished to examine the hypothesis proposed by Smith [1] that staggered spacing is a particularly important scaling parameter for boundary layer thickness; the results of these tests and those of Hunter and Cumpsty [2] tend to suggest that it is tip clearance which is most potent in determining boundary-layer integral thicknesses. The integral thicknesses agree quite well with those published by Smith.

Large-eddy simulations of tip leakage and secondary flows in an axial compressor cascade using a near-wall turbulence model

2009 ◽  
Vol 223 (6) ◽  
pp. 645-655 ◽  
Author(s):  
D Borello ◽  
G Delibra ◽  
K Hanjalić ◽  
F Rispoli
Keyword(s):  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Wall Region ◽  
Compressor Cascade ◽  
Tip Leakage ◽  
Computational Mesh ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Near Wall

This paper reports on the application of unsteady Reynolds averaged Navier—Stokes (U-RANS) and hybrid large-eddy simulation (LES)/Reynolds averaged Navier—Stokes (RANS) methods to predict flows in compressor cascades using an affordable computational mesh. Both approaches use the ζ— f elliptic relaxation eddy-viscosity model, which for U-RANS prevails throughout the flow, whereas for the hybrid the U-RANS is active only in the near-wall region, coupled with the dynamic LES in the rest of the flow. In this ‘seamless’ coupling the dissipation rate in the k-equation is multiplied by a grid-detection function in terms of the ratio of the RANS and LES length scales. The potential of both approaches was tested in several benchmark flows showing satisfactory agreement with the available experimental results. The flow pattern through the tip clearance in a low-speed linear cascade shows close similarity with experimental evidence, indicating that both approaches can reproduce qualitatively the tip leakage and tip separation vortices with a relatively coarse computational mesh. The hybrid method, however, showed to be superior in capturing the evolution of vortical structures and related unsteadiness in the hub and wake regions.

scholarly journals A Note on Interior Pathways in the Meridional Overturning Circulation

2018 ◽  
Vol 48 (3) ◽  
pp. 643-646 ◽  
Author(s):  
Joseph Pedlosky
Keyword(s):  
Boundary Layers ◽  
Turbulent Flows ◽  
Intrinsic Property ◽  
Reynolds Numbers ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Source To Sink ◽  
Basin Geometry ◽  
Meridional Overturning ◽  
Source Sink

AbstractA simple oceanic model is presented for source–sink flow on the β plane to discuss the pathways from source to sink when transport boundary layers have large enough Reynolds numbers to be inertial in their dynamics. A representation of the flow as a Fofonoff gyre, suggested by prior work on inertial boundary layers and eddy-driven circulations in two-dimensional turbulent flows, indicates that even when the source and sink are aligned along the same western boundary the flow must intrude deep into the interior before exiting at the sink. The existence of interior pathways for the flow is thus an intrinsic property of an inertial circulation and is not dependent on particular geographical basin geometry.

A State-of-the-Art CFD Setup for Axial Compressors: Details and Validation

2020 ◽  
Author(s):  
Lorenzo Cozzi ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Savino Depalo ◽  
Pio Astrua ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Power Plants ◽  
State Of The Art ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Cfd Modelling ◽  
Axial Compressors ◽  
Surge Margin ◽  
Wide Range

Abstract The overall fraction of the power produced by renewable sources in the energy market has significantly increased in recent years. The power output of most of these clean sources is intrinsically variable. At present day and most likely in the upcoming future, due to the lack of inexpensive and reliable large energy storage systems, conventional power plants burning fossil fuels will still be part of the energy horizon. In particular, power generators able to promptly support the grid stability, such as gas turbines, will retain a strategic role. This new energy scenario is pushing gas turbine producers to improve the flexibility of their turbomachines, increasing the need for reliable numerical tools adopted to design and validate the new products also in operating conditions far from the nominal one. Especially when dealing with axial compressors, i.e. machines experiencing intense adverse pressure gradients, complex flow structures and severe secondary flows, CFD modelling of offdesign operation can be a real challenge. In this work, a state-of-the art CFD framework for RANS analysis of axial compressors is presented. The various aspects involved in the whole setup are discussed, including boundary conditions, meshing strategies, mixing planes modelling, tip clearance treatment, shroud leakages and turbulence modelling. Some experiences about the choice of these aspects are provided, derived from a long-date practice on this kind of turbomachines. Numerical results are reported for different full-scale compressors of the Ansaldo Energia fleet, covering a wide range of operating conditions. Furthermore, details about the capability of the setup to predict compressor performance and surge-margin have been added to the work. In particular, the setup surge-margin prediction has been evaluated in an operating condition in which the turbomachine experiences experimental stall. Finally, thanks to several on-field data available at different corrected speeds for operating conditions ranging from minimum to full load, a comprehensive validation of the presented numerical framework is also included in the paper.

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