جستجوی مقالات مرتبط با کلیدواژه « Wall effect » در نشریات گروه « فنی و مهندسی »

Taking the electric eel as a bionic object, a long undulatory fin is designed. The turbulent model standard k-ε is used to solve the N‒S equation of a three-dimensional unsteady incompressible fluid. The hydrodynamic characteristics of the undulatory fin are studied, and the influence of the swing angle, wave frequency and ground effects on the propulsion performance of the undulatory fin are discussed. The mathematical models of the average thrust and average lateral force of the undulatory fin are established by using multiple linear regression. The results show that the thrust and lateral force of the undulatory fin increase with increasing swing angle and swing frequency, but in a motion period, the number of fluctuations of the thrust is approximately twice that of the lateral force. The relationship between the average thrust force and the average lateral force of the undulatory fin and the wave frequency and the maximum swing angle satisfies a specific exponential law. When the undulating fin moves near the wall (d ≤0.2 W), due to the coupling between the vortex at the lower edge and the tail vortex where part of the vortex is transferred to the two sides, the total thrust decreases, and the lateral force increases.

Wall-to-bed (or wall-to-fluid) heat transfer issues in trickle bed reactors (TBR) has an important impact on operation and efficiency in this category of reactors. In this study, the hydrodynamic and thermal behavior of trickle bed reactors was simulated by means of computational fluid dynamics (CFD) technique. The multiphase behavior of trickle bed reactor was studied by the implementation of the Eulerian-Eulerian multiphase approach. Also, bed porosity effect was modeled by porosity function method. In order to study the effect of operating parameters on wall-to-bed heat transfer, the influence of catalyst particle diameter and catalytic bed porosity was investigated on wall-to-bed Nu number. The results showed that the enhancement of catalytic bed porosity from 0.36 to 0.5 decreases the Nu number about 15% due to a reduction of liquid velocity adjacent to the reactor wall. Also, the increase of particle diameter from 4 to 6 millimeter decreases wall-to-bed Nu number about 15% owing to a reduction in liquid phase volume fraction.

This paper evaluates the added resistance of a torpedo shape AUV, moving inside a water pipeline, due to wall effects within the tube. Today, there are long length pipelines of water or petroleum that need to regular inspection. Early detection of failure will help to prevent breakdown and avoid the huge cost of an accident. As pipelines are enclosed environments and difficult to access, pipeline inspection robots are increasingly used for routine inspection and early failure detection. In the engineering cases, the pipes are full of liquid because there is no possibility for evacuating the pipe and interrupting the liquid transfer. It may be with or without flow of water. Therefore, the AUV must be able to afloat inside the pipe and perform non-contact inspection. In dry pipes, inspection device has contact with the walls and moves on them but in full pipes, the AUV moves such as a torpedo or submarine. The pipes have limited diameter and because of the wall effects on the fluid flow around the AUV, the resistance will be more than the free flow condition. This added resistance should be accounted accurately because it is necessary for determination of vehicle speed, power demand, range and duration of operation. This paper considers a torpedo shape AUV moving inside the pipes with the different diameter. The resistance of this modeling will be compared with the resistance of free steam modeling. This analysis is performed by the Flow Vision (V.2.3) software based on CFD method and solving the RANS equations.