Υπολογιστική μελέτη μόνιμης και μη μόνιμης ροής σε στένωση αγωγού με αδιαβατικά και μη αδιαβατικά τοιχώματα

Abstract

Υπολογιστική μελέτη μόνιμης και μη μόνιμης ροής σε στένωση αγωγού με αδιαβατικά και μη αδιαβατικά τοιχώματα.

In the context of this diploma thesis a commercial software package was used (Fluent, Gambit) for the computational study of the flow in a three dimensional symmetrical straight tube stenosis model with an area reduction of 75%. Specifically, the flow field was tested with steady conditions for nine Reynolds numbers Re=8,26,43,64,80,143,214,320,500, on the pressure drop, recirculation zone, vortisity, wall shear stress, the area were the flow is affected after the stenosis and the velocity distribution. The unsteady flow field was tested for numbers Re= 26, 43, 80,214,320,500, on a steady supply, with temperature difference (&)=5 C) on the point of the neck relative to the temperature of the fluid which was at 20 C. The temperature distribution on the field was studied, after the stenosis and the results are presented at the moment of time t=60s, in relation with the gravity. The case of an unsteady flow was tested for a Womersley number =5,31. The rate of variation between the maximum and the minimum wall shear stress was studied, on its application point and the observation of the rate of variation on the recirculation area and the velocity profile in relation to time. The results have shown a dependence of the flow recirculation zone, of the temperature distribution, the pressure difference before and after the stenosis and the alternation of the wall shear stress on different positions from positive to negative values, by the Reynolds number. The direction of the acceleration of gravity was found to substantially affect the velocity and temperature field on the area after the stenosis, making the effect of the buoyancy phenomena more perceptible varying the recirculation zone asymmetrically, depending on the orientation of the model. Furthermore it was found that there is a dependence of the distribution of the wall shear stress and evolution of the recirculation zone, from the waveform of the fluid’s supply pulse, which makes the velocity field after the stenosis complex, especially on the deceleration phase.