Time-dependent tube flow of compressible suspensions subject to pressure dependent wall slip: Ramifications on development of flow instabilities

2008 ◽  
Vol 52 (5) ◽  
pp. 1069-1090 ◽  
Author(s):  
H. S. Tang ◽  
Dilhan M. Kalyon
Keyword(s):  
Wall Slip ◽  
Time Dependent ◽  
Flow Instabilities ◽  
Tube Flow

Comparison of Axial Water and Air Injections in the Draft Tube of a Francis Turbine for RVR Mitigation

2021 ◽  
Author(s):  
Subodh Khullar ◽  
Krishna M. Singh ◽  
Michel J. Cervantes ◽  
Bhupendra K. Gandhi
Keyword(s):  
Pressure Pulsation ◽  
Draft Tube ◽  
Water Injection ◽  
Air Injection ◽  
Flow Instabilities ◽  
Pressure Recovery ◽  
Francis Turbine ◽  
Tube Flow ◽  
Pressure Pulsations ◽  
Jet Injection

Abstract The presence of excessive swirl at the runner outlet in Francis turbines operating at part load leads to the development of flow instabilities such as the rotating vortex rope (RVR). The presence of RVR causes severe pressure pulsations, power swings, and fatigue damage in the turbine unit. Air and water injection in the draft tube have been reported to reduce the detrimental effects of RVR formation in the Francis turbines. Air injection is one of the oldest and most widely used methods. In contrast, water jet injection is a relatively new methodology. The present work reports the numerical simulations performed to compare the respective effectiveness of these methods to mitigate the RVR and the related flow instabilities. The efficacy of the two methods has been compared based on the pressure pulsations and pressure recovery in the draft tube cone. The results show that the air and water injection influence the draft tube flow field in different ways. Both air and water injection led to a reduction in pressure pulsation magnitudes in the draft tube cone. However, the air injection led to a negative pressure recovery while the water injection improved the draft tube action.

Wall slip determination for coarse food suspensions in tube flow at high temperatures

2005 ◽  
Vol 70 (1) ◽  
pp. 73-81 ◽  
Author(s):  
Krittalak Chakrabandhu ◽  
Rakesh K. Singh
Keyword(s):  
High Temperatures ◽  
Wall Slip ◽  
Tube Flow

Theoretical Study of Flow Instabilities and Inlet Distortions in Axial Compressors

1982 ◽  
Vol 104 (3) ◽  
pp. 715-721 ◽  
Author(s):  
P. Ferrand ◽  
J. Chauvin
Keyword(s):  
Theoretical Study ◽  
Rotating Stall ◽  
Time Dependent ◽  
Flow Instabilities ◽  
Axial Compressors ◽  
Independent Variables ◽  
Servo Mechanism ◽  
Dependent Variables ◽  
Multistage Compressors ◽  
Method Of Evaluation

This paper describes a method of evaluation of the single and multistage compressors response to steady and unsteady inlet distortions. It allows also the evaluation of the appearance of unstable regimes and their characterization (rotating stall and surge). It is based on a linearized approach using mean line calculations. The compressor is considered as a series of vaned and vaneless spaces, and the corresponding equations are solved by use of Fourier series for time independent variables and by Laplace’s transform for time-dependent variables. An analogy between the compressor’s response and a servo-mechanism is developed, using Nyquist’s diagram. Results are compared with experimental data which prove the validity of the approach. A parametric study indicates which parameters can be modified to improve the flow stability.

Theoretical Study of Flow Instabilities and Inlet Distortions in Axial Compressors

1981 ◽  
Author(s):  
P. Ferrand ◽  
J. Chauvin
Keyword(s):  
Theoretical Study ◽  
Rotating Stall ◽  
Time Dependent ◽  
Flow Instabilities ◽  
Axial Compressors ◽  
Independent Variables ◽  
Servo Mechanism ◽  
Dependent Variables ◽  
Multistage Compressors ◽  
Method Of Evaluation

This paper describes a method of evaluation of the single and multistage compressors response to steady and unsteady inlet distortions. It allows also the evaluation of the appearance of unstable regimes and their characterization (rotating stall and surge). It is based on a linearized approach using mean line calculations. The compressor is considered as a serie of vaned and vaneless spaces, and the corresponding equations are solved by use of Fourier series for time independent variables and by Laplace’s transform for time dependent variables. An analogy between the compressor’s response and a servo-mechanism is developed, using Nyquist’s diagram. Results are compared with experimental data which prove the validity of the approach. A parametric study indicates which parameters can be modified to improve the flow stability.

Unsteady Laminar Forced-Convective Tube Flow Under Dynamic Time-Dependent Heat Flux

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
M. Fakoor-Pakdaman ◽  
Mehdi Andisheh-Tadbir ◽  
Majid Bahrami
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Analytical Model ◽  
Time Dependent ◽  
Bulk Temperature ◽  
Fluid Temperature ◽  
Tube Flow ◽  
Flux Boundary Condition ◽  
Arbitrary Time

A new all-time model is developed to predict transient laminar forced convection heat transfer inside a circular tube under arbitrary time-dependent heat flux. Slug flow (SF) condition is assumed for the velocity profile inside the tube. The solution to the time-dependent energy equation for a step heat flux boundary condition is generalized for arbitrary time variations in surface heat flux using a Duhamel's integral technique. A cyclic time-dependent heat flux is considered and new compact closed-form relationships are proposed to predict (i) fluid temperature distribution inside the tube, (ii) fluid bulk temperature and (iii) the Nusselt number. A new definition, cyclic fully developed Nusselt number, is introduced and it is shown that in the thermally fully developed region the Nusselt number is not a function of axial location, but it varies with time and the angular frequency of the imposed heat flux. Optimum conditions are found which maximize the heat transfer rate of the unsteady laminar forced-convective tube flow. We also performed an independent numerical simulation using ansys fluent to validate the present analytical model. The comparison between the numerical and the present analytical model shows great agreement; a maximum relative difference less than 5.3%.

Transient Solidification in Flow into a Rod Bundle

1980 ◽  
Vol 102 (2) ◽  
pp. 330-334 ◽  
Author(s):  
M. Epstein ◽  
L. J. Stachyra ◽  
G. A. Lambert
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Approximate Method ◽  
Axial Flow ◽  
Hydraulic Diameter ◽  
Time Dependent ◽  
Tube Flow ◽  
Liquid Mass ◽  
Rod Bundle

Transient solidification of a liquid in axial flow into and through a cold rod bundle was investigated. Experiments are described in which the amount of liquid displaced through the rod bundle before freezing shut as a function of pressure drop was measured. Simple relations for the liquid mass displaced into or through the rod bundle were derived by combining the notion of a time-dependent hydraulic diameter with an available approximate method for treating transient solidification in a tube flow. The relations are shown to be approximately consistent with the experimental data.

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