scholarly journals Propagating Stall in Compressors With Porous Walls

1975 ◽  
Author(s):  
J. H. Horlock ◽  
C. M. Lakhwani
Keyword(s):  
Unsteady Flow ◽  
Radial Flow ◽  
Flow Instability ◽  
Porous Wall ◽  
Flow Coefficient ◽  
Compressor Blades ◽  
Axial Compressors ◽  
Flow Through ◽  
Porous Walls ◽  
End Wall

A modification is presented to the Emmons/Stenning analysis for predicting stall propagation, taking into account the unsteady flow through the end wall of a cascade row of compressor blades. It is shown that if radial flow from the blade channels is permitted, then the condition for flow instability is changed. The expression obtained for the flow coefficient at which stall occurs indicates an improvement in operating range, with virtually no effect on stall cell speed. Experimental evidence suggests that a mechanism such as that described may be the reason for the delay in stall onset produced by porous wall treatment of axial compressors.

Flow Through Cascades of Slotted Compressor Blades

1970 ◽  
Vol 92 (1) ◽  
pp. 57-64 ◽  
Author(s):  
A. A. Mikolajczak ◽  
H. D. Weingold ◽  
J. P. Nikkanen
Keyword(s):  
Flow Analysis ◽  
Axial Flow ◽  
Limited Range ◽  
Wall Region ◽  
Compressor Blades ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Flow Through ◽  
Wake Model ◽  
End Wall

The performance of axial flow compressors can be improved when it becomes possible to achieve higher loading per stage than currently attainable. The major obstacles to attaining this objective are the limitations on loading in the end wall region and the limited range of operating incidence of compressor blades. A possible method of achieving a wide range of operating incidence is the use of slotted or multibody airfoils. An incompressible, two-dimensional, potential flow analysis for thick, highly cambered multibodies in cascade is presented. The analysis is extended to include compressibility. A boundary-layer calculation, including a wake model, is described and used to predict cascade losses. Theoretical predictions are compared against slotted and unslotted cascade and compressor stator experimental results and adequate agreement obtained. The slotted blade concept is shown to offer performance benefits, provided that end-wall loading limitations can be overcome.

The Determination of End-Wall Blockage in Axial Compressors: A Comparison Between Various Approaches

1999 ◽  
Vol 122 (2) ◽  
pp. 218-224 ◽  
Author(s):  
J. H. Horlock
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Equilibrium State ◽  
Axial Compressors ◽  
Displacement Thickness ◽  
Flow Through ◽  
The Subject ◽  
Wall Blockage ◽  
End Wall

The end-wall blockage in axial compressors has been the subject of several investigations over a period of many years. This paper reviews and compares various approaches to determining the blockage, particularly in the “repeating” stage, a stage deeply embedded in the compressor where an equilibrium state is reached, the flow through any one stage repeating in the next. These approaches include: (i) correlations of displacement thickness measured in compressor rigs; (ii) a relationship between outlet blockage and the clearance area, based both on an empirical development of a simple model of the flow through the clearance space and full CFD calculations of the flow; (iii) momentum analysis of the flow through the blockage region, developed from the boundary layer analyses of some years ago, but not now relying on boundary layer concepts. [S0889-504X(00)01502-6]

scholarly journals Mathematical study on two-fluid model for flow of K–L fluid in a stenosed artery with porous wall

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
R. Ponalagusamy ◽  
Ramakrishna Manchi
Keyword(s):  
Theoretical Study ◽  
Fluid Model ◽  
Porous Wall ◽  
Governing Equations ◽  
Rate Of Increase ◽  
Special Cases ◽  
Stenosed Artery ◽  
Flow Through ◽  
Two Fluid Model ◽  
Two Fluid

AbstractThe present communication presents a theoretical study of blood flow through a stenotic artery with a porous wall comprising Brinkman and Darcy layers. The governing equations describing the flow subjected to the boundary conditions have been solved analytically under the low Reynolds number and mild stenosis assumptions. Some special cases of the problem are also presented mathematically. The significant effects of the rheology of blood and porous wall of the artery on physiological flow quantities have been investigated. The results reveal that the wall shear stress at the stenotic throat increases dramatically for the thinner porous wall (i.e. smaller values of the Brinkman and Darcy regions) and the rate of increase is found to be 18.46% while it decreases for the thicker porous wall (i.e. higher values of the Brinkman and Darcy regions) and the rate of decrease is found to be 10.21%. Further, the streamline pattern in the stenotic region has been plotted and discussed.

scholarly journals Periodic flow structures in a turbofan fan stage in windmilling

2020 ◽  
pp. 095441002094829
Author(s):  
Nicolás García Rosa ◽  
Adrien Thacker ◽  
Guillaume Dufour
Keyword(s):  
Mass Flow ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Variable Mass ◽  
Flow Coefficient ◽  
Test Bed ◽  
Ambient Conditions ◽  
Low Velocity ◽  
Blade Passing Frequency ◽  
Flow Through

In a fan stage under windmilling conditions, the stator operates under negative incidence, leading to flow separation, which may present an unsteady behaviour due to rotor/stator interactions. An experimental study of the unsteady flow through the fan stage of a bypass turbofan in windmilling is proposed, using hot-wire anemometry. Windmilling conditions are reproduced in a ground engine test bed by blowing a variable mass flow through a bypass turbofan in ambient conditions. Time-averaged profiles of flow coefficient are independent of the mass flow, demonstrating the similarity of velocity triangle. Turbulence intensity profiles reveal that the high levels of turbulence production due to local shear are also independent of the inlet flow. A spectral analysis confirms that the flow is dominated by the blade passing frequency, and that the separated regions downstream of the stator amplify the fluctuations locked to the BPF without adding any new frequency. Phase-locked averaging is used to capture the periodic wakes of the rotor blades at the rotor/stator interface. A spanwise behaviour typical of flows through windmilling fans is evidenced. Through the inner sections of the fan, rotor wakes are thin and weakly turbulent, and the turbulence level remains constant through the stage. The rotor wakes thicken and become more turbulent towards the fan tip, where flow separation occurs. Downstream of the stator, maximum levels of turbulence intensity are measured in the separated flow. Large periodical zones of low velocity and high turbulence intensity are observed in the outer parts of the separated stator wake, confirming the pulsating motion of the stator flow separation, locked at the blade passing frequency. Space-time diagrams show that the flow is chorochronic, and a 2 D non-linear harmonic simulation is able to capture the main interaction modes, however, the stator incidence distribution could be affected by 3 D effects.

Capillary water absorption by a porous cylinder

2017 ◽  
Vol 42 (2) ◽  
pp. 120-124 ◽  
Author(s):  
Christopher Hall
Keyword(s):  
Radial Flow ◽  
Effective Porosity ◽  
Capillary Absorption ◽  
Porous Cylinder ◽  
Capillary Water ◽  
Cylinder Axis ◽  
Flow Through ◽  
Front Model ◽  
Sharp Front ◽  
Good Agreement

Capillary absorption (imbibition) of water by a porous cylinder is described by means of a Sharp-Front model. The cumulative absorption increases as (time)1/2 at early times, but more slowly as the wet front approaches the cylinder axis. Results are given in terms of dimensionless variables. Experimental data on plaster cylinders are in good agreement with theory. Estimates of the sorptivity and effective porosity of the material can be obtained. The model may be useful in testing drilled cores and may also be applied to radial flow through the wall of a porous tube (hence to conduits and arches).

scholarly journals Simplified Method for Flow Analysis and Performance Calculation Through an Axial Compressor

1984 ◽  
Author(s):  
Hubert Miton ◽  
Youssef Doumandji ◽  
Jacques Chauvin
Keyword(s):  
Equations Of Motion ◽  
Computing Time ◽  
Flow Analysis ◽  
Axial Compressor ◽  
Computation Method ◽  
Duct Flow ◽  
Axial Compressors ◽  
Flow Through ◽  
And Performance ◽  
Performance Calculation

This paper describes a fast computation method of the flow through multistage axial compressors of the industrial type. The flow is assumed to be axisymmetric between the blade rows which are represented by actuator disks. Blade row losses and turning are calculated by means of correlations. The equations of motion are linearized with respect to the log of static pressure, whose variation along the radius is usually of limited extent for the type of machines for which the method has been developed. In each computing plane (i.e. between the blade rows) two flows are combined: a basic flow with constant pressure satisfying the mass flow requirements and a perturbation flow fulfilling the radial equilibrium condition. The results of a few sample calculations are given. They show a satisfactory agreement with a classical duct flow method although the computing time is reduced by a factor five. The method has also been coupled with a surge line prediction calculation.

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