Vaneless Diffuser Rotating Stall Based on Two-Dimensional Inviscid Flow Analysis. 1st Report, Linear Analysis.

Rotating stalls in vaneless diffusers are studied from the viewpoint that they are basically two-dimensional inviscid flow instability under the boundary conditions of vanishing velocity disturbance at the diffuser inlet and of vanishing pressure disturbance at the diffuser outlet. The linear analysis in the present report shows that the critical flow angle and the propagation velocity are functions of only the diffuser radius ratio. It is shown that the present analysis can reproduce most of the general characteristics observed in experiments: critical flow angle, propagation velocity, velocity, and pressure disturbance fields. It is shown that the vanishing velocity disturbance at the diffuser inlet is caused by the nature of impellers as a “resistance” and an “inertial resistance,” which is generally strong enough to suppress the velocity disturbance at the diffuser inlet. This explains the general experimental observations that vaneless diffuser rotating stalls are not largely affected by the impeller.

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Rotating Stall Characteristics in a Wide Vaneless Diffuser

Volume 6: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68445 ◽

2005 ◽

Cited By ~ 1

Author(s):

S. Ljevar ◽

H. C. de Lange ◽

A. A. van Steenhoven

Keyword(s):

Boundary Layers ◽

Flow Instability ◽

Stability Limit ◽

Rotating Stall ◽

Two Dimensional ◽

Vaneless Diffuser ◽

Flow Angle ◽

Wall Boundary ◽

The Stability ◽

Rotating Instability

Paper reports a numerical study on vaneless diffuser flow instability performed for the purpose of better understanding of rotating stall mechanism in radial vaneless diffusers. This analysis is restricted to the two-dimensional flow where effect of wall boundary layers is neglected. Numerical results reveal that a two-dimensional rotating flow instability similar to rotating stall occurs when critical flow angle is exceeded. They also show that the stability limit and the structure of a two dimensional rotating instability are influenced by the configuration geometry and inlet and outlet flow conditions. Good agreement with data from the literature is found for the stability limit and number and speed of propagating cells. Number of cells and their speed is somewhat higher than observed in experiments from literature. This might imply that inception point is caused by the core flow instability and that wall boundary layers are more determinative for the structure of rotating instability.

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Theory of Finite Disturbances in a Centrifugal Compression System With a Vaneless Radial Diffuser

Volume 1: Turbomachinery ◽

10.1115/91-gt-082 ◽

1991 ◽

Cited By ~ 3

Author(s):

F. K. Moore

Keyword(s):

Boundary Layer ◽

Previous Analysis ◽

Inviscid Flow ◽

Linear Analysis ◽

Rotating Stall ◽

Flow Coefficient ◽

Displacement Effect ◽

Compression System ◽

Nonlinear Transient ◽

Rotating Wave

A previous small-perturbation analysis of circumferential waves in centrifugal compression systems, assuming inviscid flow, is first shown to be consistent with observations that narrow diffusers are more stable than wide ones, when boundary-layer displacement effect is included. Then, a previous analysis for finite-strength transients containing both surge and rotating stall in axial machines is adapted for a centrifugal compression system. Under certain assumptions, and except for a new second-order swirl, the diffuser velocity field, including resonant singularities, can be carried over from the previous inviscid, linear analysis. Nonlinear transient equations are derived and applied in a simple example to show that throttling through a resonant value of flow coefficient must occur in a sudden surge-like drop, accompanied by a transient rotating wave. This “inner” solution is superseded by an “outer” surge response on a longer time scale. Numerical results are shown for various parametric choices relating to throttle schedule and the characteristic slope.

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Two-Dimensional Rotating Stall Analysis in a Wide Vaneless Diffuser

International Journal of Rotating Machinery ◽

10.1155/ijrm/2006/56420 ◽

2006 ◽

Vol 2006 ◽

pp. 1-11 ◽

Cited By ~ 24

Author(s):

S. Ljevar ◽

H. C. de Lange ◽

A. A. van Steenhoven

Keyword(s):

Flow Instability ◽

Numerical Study ◽

Rotating Stall ◽

Parameter Analysis ◽

Two Dimensional ◽

Vaneless Diffuser ◽

Core Flow ◽

Flow Solver ◽

Incompressible Viscous Flow ◽

Commercial Code

We report a numerical study on the vaneless diffuser core flow instability in centrifugal compressors. The analysis is performed for the purpose of better understanding of the rotating stall flow mechanism in radial vaneless diffusers. Since the analysis is restricted to the two-dimensional core flow, the effect of the wall boundary layers is neglected. A commercial code with the standard incompressible viscous flow solver is applied to model the vaneless diffuser core flow in the plane parallel to the diffuser walls. At the diffuser inlet, rotating jet-wake velocity pattern is prescribed and at the diffuser outlet constant static pressure is assumed. Under these circumstances, two-dimensional rotating flow instability similar to rotating stall is found to exist. Performed parameter analysis reveals that this instability is strongly influenced by the diffuser geometry and the inlet and outlet flow conditions.

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A Theoretical Model for Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239760 ◽

1985 ◽

Vol 107 (2) ◽

pp. 507-513 ◽

Cited By ~ 29

Author(s):

P. Frigne ◽

R. Van den Braembussche

Keyword(s):

Theoretical Model ◽

Centrifugal Compressor ◽

Static Pressure ◽

Inviscid Flow ◽

Rotating Stall ◽

Vaneless Diffuser ◽

Flow Core ◽

Flow Angle ◽

Unsteady Boundary Layers ◽

Number Of Cells

A theoretical model for rotating stall in the vaneless diffuser of a centrifugal compressor is presented. It consists of a time-evolutive calculation of the strong interaction between the inviscid flow core and the unsteady boundary layers along the walls. It is shown that, depending on the diffuser geometry and the diffuser inlet flow angle, a transient perturbation of the outlet static pressure will generate a rotating flow pattern, if the periodicity of this perturbation corresponds to the experimentally observed number of cells. The relative rotational speed and the phase relation between the velocity and the flow angle variations are also in agreement with experimental data.

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Flow analysis in two-dimensional impeller of centrifugal pump by the surface singularity method combined with a flow-model of three-dimensional boundary layer.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.53.3038 ◽

1987 ◽

Vol 53 (494) ◽

pp. 3038-3043

Author(s):

Akinori FURUKAWA ◽

Ci-Chang CHENG ◽

Takakichi SEKIYA ◽

Yasuo TAKAMATSU

Keyword(s):

Boundary Layer ◽

Centrifugal Pump ◽

Flow Model ◽

Flow Analysis ◽

Three Dimensional ◽

Surface Singularity ◽

Two Dimensional ◽

Singularity Method ◽

Dimensional Boundary

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Optimization of the Three-Dimensional Flow Path in the Scroll-Nozzle System of a Radial Inflow Turbine

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239600 ◽

1984 ◽

Vol 106 (2) ◽

pp. 511-515 ◽

Cited By ~ 1

Author(s):

E. A. Baskharone

Keyword(s):

Flow Analysis ◽

Three Dimensional ◽

Inviscid Flow ◽

Three Dimensional Flow ◽

Multiply Connected ◽

Dimensional Flow ◽

Nozzle Configuration ◽

Flow Domain ◽

Radial Inflow Turbine ◽

Compressibility Effects

A three-dimensional inviscid flow analysis in the combined scroll-nozzle system of a radial inflow turbine is presented. The coupling of the two turbine components leads to a geometrically complicated, multiply-connected flow domain. Nevertheless, this coupling accounts for the mutual effects of both elements on the three-dimensional flow pattern throughout the entire system. Compressibility effects are treated for an accurate prediction of the nozzle performance. Different geometrical configurations of both the scroll passage and the nozzle region are investigated for optimum performance. The results corresponding to a sample scroll-nozzle configuration are verified by experimental measurements.

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