Sharif Digital Repository

This study provides a stability analysis of flexible rotating pipes taking into account the simultaneous effects of internal and external fluid loading. Using the Euler-Bernoulli beam assumptions, governing equations for flexural vibrations of rotating pipes are obtained. The internal flow characteristics and the double gyroscopic effect are taken into account when deriving the structural equations coupled with the internal flow. External fluid loading is determined by a special linearization of the Navier-Stokes equations. Considering the circular wall of the pipe as an impermeable boundary to the flow, fluid-induced forcing functions are obtained and then applied to the structural... 

This study provides a stability analysis of flexible rotating pipes taking into account the simultaneous effects of internal and external fluid loading. Using the Euler-Bernoulli beam assumptions, governing equations for flexural vibrations of rotating pipes are obtained. The internal flow characteristics and the double gyroscopic effect are taken into account when deriving the structural equations coupled with the internal flow. External fluid loading is determined by a special linearization of the Navier-Stokes equations. Considering the circular wall of the pipe as an impermeable boundary to the flow, fluid-induced forcing functions are obtained and then applied to the structural... 

In this investigation, the Flexible String Algorithm (FSA) used before for the inverse design of 2D subsonic ducts is developed and applied for the inverse design of subsonic and supersonic ducts with and without normal shock waves. In this method, the duct wall shape is changed under a novel algorithm based on the deformation of a virtual flexible string in a flow. Deformation of the string due to the local fl.ow conditions resulting from changes in the wall geometry is performed until the target shape satisfying the. prescribed walls pressure distribution is achieved. The flow field at each shape modification step is analyzed using an Euler equation solution by the. A USM method. Some... 

Enhancement of heat transfer is investigated in an experimental study of ferrofluid flow in a tube subjected to a constant and uniform heat flux on its wall, filled with permeable material under the effect of magnetic field. Effect of ferrofluid volume fraction, Reynolds number, and different frequencies of various magnetic field modes on heat transfer is examined by measuring the temperature on the wall. Using ferrofluid under the effect of magnetic field improves the heat transfer, and porous media makes the temperature distribution more uniform. Volumetric percentage of nano-particles has the greatest effect on the heat transfer  

In this paper, numerical and experimental investigation of the performance and internal flow field characteristics of the twinentry radial inflow turbine under full and partial admission conditions are presented. The turbine is tested on a turbocharger test facility, which was developed for small and medium size turbochargers. The flow pattern in the volute and impeller of a twin-entry turbine is analyzed using fully three-dimensional viscous program. The computational performance results are compared with the experimental results, and good agreement is found. The flow field at the outlet of the turbine is investigated using a five-hole pressure probe. The tests are performed for both full... 

A modified weakly compressible smoothed particle hydrodynamics (WCSPH) is presented, which utilizes consistent discretization schemes for spatial derivatives in the flow equations. Here, each SPH particle is considered as a computational point that represents a specific part of the fluid. To overcome non-physical oscillations that usually arise in standard WCSPH, we modified the mass conservation equation by using a numerical filter. This modification is based on the difference between two discretization schemes used for the term ∇{dot operator}∇Pρ. Furthermore, a new implementation of wall boundary condition in SPH is introduced. This condition is imposed on the pressure of wall boundary... 

In this paper, a numerical and experimental investigation of the performance and internal flow field characteristics of the twin-entry radial inflow turbine under full and partial admission conditions are presented. The turbine is tested on a turbocharger test facility which was developed for small and medium size turbochargers. The flow pattern in the volute and impeller of a twin-entry turbine is analyzed using a fully three-dimensional viscous program. The computational performance results are compared with the experimental results, and good agreement is found. The flow field at the outlet of the turbine is investigated using a five-hole pressure probe. Numerical and experimental results... 

In this investigation, the flexible string algorithm (FSA), used before for inverse design of subsonic and supersonic ducts in compressible flows with and without normal shock, is developed and applied for inverse design of 2D incompressible viscous internal flow with and without separation. In the proposed method, the duct wall shape is changed under an algorithm based on deformation of a virtual flexible string in flow. At each modification step, the difference between current and target wall pressure distributions is applied to the string. The method is an iterative inverse design method and utilizes the analysis code for the flow field solution as a black-box. Some validation test cases... 

Rarefied gas flow in micro/nano electro mechanical systems (MEMS/NEMS) does not perform exactly as that in macro-scale devices. The main goal in this study is to investigate mixed subsonic-supersonic flows in micro/nano channels and nozzles and to provide physical descriptions on their behaviors. We use DSMC method as a reliable numerical tool to extend our simulation. It is because the DSMC provides accurate solution for the Boltzmann equations over the entire range of rarefied flow regime or Knudsen numbers. As is known, the appearance of oblique/normal shocks at the inlet of a channel or a nozzle adds to the complexity of internal flow field analyses. We found some very unique physical... 

A fully coupled formulation of thermo-fluid shape design problems has recently been developed in which the unknown nodal coordinates appear explicitly in the formulation of the problem. This "direct design" approach is, in principle, generally applicable and has been successfully applied in the context of potential and Euler flow models. This paper focuses on the direct design of ducts using the ideal flow model and may be considered as an addendum to the paper entitled "Direct Design of Ducts" [1]. However, a cell-vertex finite volume method is used and a different boundary condition implementation technique is applied, as compared to the method presented in the previous paper. The other... 

Flow turbulators have promising heat transfer applications. Here, the novel design proposed in our previous study (vibrational ball turbulators, VBTs, mounted on an elastic wire inside a circular tube) is investigated experimentally from heat transfer and thermal performance standpoints. The effects of diameter (Y) and longitudinal distance (pitch, X) ratios of VBTs, the Reynolds number, and the axial tension of the wire (σ0) on the average Nusselt number (Nu), the average Nusselt number ratio (Nu divided by that of a plain tube, Nup), the friction factor ratio (f/fp), and a parameter called the thermal performance factor (η=(Nu/Nup)/(f/fp)1/3) are studied. Different ball diameter (Y=0.3,... 

This paper presents numerical and experimental investigation of the performance and internal flow field characteristics of twin-entry radial inflow turbines at full and extreme partial admission conditions. The turbine is tested on a turbocharger test facility, which was developed for small and medium size turbochargers. Experimental results show that the lowest efficiency corresponds to extreme conditions. Therefore, flow field analyzing is employed to consider these conditions. The flow pattern in the volute and impeller of a twin-entry turbine is analyzed using an in-house fully three-dimensional viscous flow solver. The computational performance results are compared with the experimental... 

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares different geometries for numerical investigation of the 3D flow in the runner of a Francis turbine, and presents an optimum geometry with least computational effort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal flows, 1989) in which the geometry and detailed best efficiency...