Wyniki wyszukiwania - BazTech

1

3D simulation of incompressible flow around a rotating turbulator: Effect of rotational and direction speed

Zoubai Elhadi, Laidoudi Houssem, Tlanbout Ismail, Makinde Oluwole Daniel

Archives of Thermodynamics

|

2023

|

Vol. 44, no 2

139--157

EN

This paper presents new results for the dynamic behaviour of fluid around a rotating turbulator in a channel. The turbulator has a propeller form which is placed inside a flat channel. The research was carried out using 3D numerical simulation. The rationale of the experiment was as follows: we put a propeller-turbulator inside a flat channel, and then we insert a water flow inside the channel. The turbulator rotates at a constant and uniform speed. The main points studied here are the effect of the presence of turbulator and its rotational direction on the flow behaviour behind the turbulator. The results showed that the behaviour of flow behind the turbulator is mainly related to the direction of turbulator rotating. Also, the studied parameters affect coefficients of drag force and power number. For example, when the turbulator rotates in the positive direction, the drag coefficient decreases in terms of rotational speed of the turbulator, while the drag coefficient increases in terms of rotational speed when the turbulator rotates in the negative direction.

2

Application of a near wall model to Navier-Stokes equations with nonlinear time-relaxation model

İhan Özgül

Journal of Applied Mathematics and Computational Mechanics

|

2022

|

Vol. 21, nr 2

39--50

EN

It is difficult and essential to determine appropriate boundary conditions for the flow averages because they depend on the behavior of the unknown flow near the wall. Large-eddy simulation (LES) is one of the promising approaches. LES estimates local spatial averages ū of the velocity u of the fluid. The main problem is modeling near-wall turbulence in complex geometries. Inspired by the works of Navier and Maxwell, the boundary conditions are developed on the wall. In this study, the appropriate friction coefficient for 2-D laminar flows is computed, and existing boundary layer theories are used to improve numerical boundary conditions for flow averages. The slip with friction and penetration with resistance boundary conditions are considered. Numerical tests on two-dimensional channel flow across a step using this boundary condition on the top and bottom wall and the step are performed.

3

Use of siliconised infant endotracheal tubes reduces work of breathing under turbulent flow

Stankiewicz B., Rawicz M., Darowski M., Zielinski K., Kozarski M., Chwojnowski A.

Biocybernetics and Biomedical Engineering

|

2017

|

Vol. 37, no. 1

59--65

EN

The high resistance of an infant endotracheal tube (ETT) can markedly impair ventilation and gas exchange. Since some manufacturers cover the inner surface of their ETTs with a silicon layer in order to diminish deposition and ease mucous evacuation from airway, via surface roughness decrease, we assessed whether the silicon layer may affect tube resistance, work of breathing and other parameters of ventilation. We compared SUMI (Poland) non-siliconised and siliconised polyvinyl chloride ETTs (2.5, 3.0 and 4.0 mm ID), twenty of each type and size combination. Simulating volume-controlled ventilation with the hybrid (numerical–physical) lung models of a premature infant and a 3-month-old baby peak inspiratory pressure (PIP), peak inspiratory and expiratory flow (PIF, PEF), (patient + ETT) inspiratory and expiratory airway resistance (Rins, Rexp) and work of breathing by ventilator (WOBvt) were measured. Additionally, images of the both type surfaces were taken using Hitachi TM-1000 electron microscope. When 2.5 and 3.0 mm ID ETTs were examined, laminar flow (Re <2300) across the tube was observed, and there were no clinically significant differences in the ventilation param-eters between non-siliconised and siliconised tubes. Whereas, when 4 mm ID ETTs were tested, turbulent flow was observed, and PIP, Rins, Rexp and WOBvt were significantly lower (5%, 17%, 17%, and 7%, respectively) (P < 0.05), but PIF and PEF were significantly higher (8%, 14%) (P < 0.05). Thus, the silicone inner surface of ETT offers less resistance and WOBvt in presence of turbulent flow. However, artifacts observed on the surface of non-siliconised and siliconised ETTs can potentially impair ventilation.

4

Laminar flow due to a rotating frustum of a cone

Pop I., Na T. Y.

Applied Mechanics and Engineering

|

1999

|

Vol. 4, no 1

113-120

EN

A theoretical study is carried out to investigate the steady laminar boundary layer flow due to a rotating frustum of a cone. The effects of the streamwise coordinate and half cone angle on the velocity field and local skin friction coefficient are examined.