Numerical Simulation of Cavitating Flow Over 2D Hydrofoil Using OpenFOAM Adapted for Debian Operating System With LXDE Based in Kernel GNU/Linux

Though commercial CFD codes are widely used in flow analysis, but there are free/open source programs which have been applying for computational fluid dynamics. An open source software makes it possible to customize the solver according to the flow features. In the present paper, cavitating flows over 2D NACA66 hydrofoil were simulated based on open source software, where SALOME is used for mesh generation, OpenFOAM for flow solution under Debian GNU/Linux operating system. The results show the simulated cavitating flow characteristics such as cavity revolution, vortex shedding, cavitation induced pressure vibrations, etc. are validated by experiments and results obtained from proprietary software as Ansys Fluent. Thus, the proposed numerical methods based on open source platform are suitable for flow simulations, even for depicting the complicated physics of cavitation.

Numerical Simulation of Cavitating Flow Around a Hydrofoil

The objective of this paper is to evaluate the applicability of different cavitation models and determine appropriate numerical parameters for cavitating flows around a hydrofoil. The simulations are performed for a NACA 66 foil at 6 degrees angle of attack, Reynolds number of 750 000 and for a cavitation number of 1.49 corresponding to the partial sheet cavitating regime. The incompressible, multiphase Reynolds-averaged Navier-Stokes (RANS) equations are solved by the CFD solver CFX with Kubota and Merkle cavitation models. As part of the work, the Merkle model is implemented into CFX by User Fortran code because this model has shown good cavitation prediction capability according to the literature. The effects of the k-ε and SST turbulence models on the cavitating flow dynamics are compared. Also, an investigation on structured and hybrid meshes with different mesh sizes and concentrations is carried out in order to better understand the mesh influence for this cavitation simulation. The local compressibility effect is considered by correcting the turbulent eddy viscosity inside the mixture vapor/liquid zones. The numerical results are validated by experiments conducted in a cavitation tunnel at the French Naval Academy.

Break-Up of Threads From Laminar Open Channel Flow Influenced by Cross-Wind Gas Flow

The breakup process of threads from laminar operating rotary atomizer (LamRot) is in the scope of this investigation. A similarity trail is used to investigate the influence of the thread deformation within a cross-wind flow on the thread breakup process. The threads emerge from laminar open channel flow while the liquid viscosity, the flow rate, the pipe inclination towards the gravity as well as the cross-wind velocity is varied. The breakup length and drop size distribution are analyzed by a back-light photography setup. The results thus obtained are compared with results of previous examination by Schröder [1] and Mescher [2]. It is found that the breakup length decreases and that the drop size grows with rising cross-wind intensity, while the width of the drop size distribution increases. At the same operating conditions, the breakup length for laminar open channel flow is smaller compared to completely filled capillaries. In contrast to this observation, the drop size distribution remains nearly unchanged. The critical velocity for the transition from axisymmetric to wind-induced thread breakup was found to be smaller than for completely filled capillaries.

Effect of Fluid Properties on Droplet Generation in a Microfluidic T-Junction

Over the last decade, significant work has been performed in an attempt to quantify the effect of different parameters such as flowrate, geometrical and fluid characteristics on the droplet break up mechanism in microfluidic T-Junctions. This demand is dictated by the need of tight control of the size and dispersity of the droplets generated in such geometries. Even though several researchers have investigated the effect of viscosity ratio on both the droplet break up mechanism as well as on the regime transition, fluid properties have not been included in most scaling laws. It is therefore evident that the contribution of fluid properties has not been quantified thoroughly. In the present work, the effect of fluid properties on the volume of droplets generated in a microfluidic T-junction is investigated. The main aim of this work is to examine the influence of viscosity of both the dispersed and continuous phase as well as the effect of interfacial tension on the size of droplet generated along with the break up mechanism. Three different oils have been utilised as continuous phase in this work to enable investigation of the effect of viscosity of the continuous phase with experiments performed at constant Capillary numbers. Various glycerol weight percentages have been employed to vary the viscosity of the dispersed phase fluid (water). Lastly, the effect of interfacial tension has been explored using two of the oils at constant μcUc (viscous force term). High speed imaging has been utilised to visualise and measure the volume of the resulting droplets. The viscosity ratio (viscosity of dispersed phase over viscosity of continuous phase) between the two phases appears to affect the droplet generation mechanism, especially for the highest viscosity ratio employed (mineral oil-water system) where the system behaves in a noticeably different way. Influence of interfacial tension is also noticeable even though less evident. In terms of the effect of viscosity of dispersed phase on the droplet generation a small difference on the volume of the droplets generated in olive oil glycerol systems is also reported. In an attempt to enumerate the effect of fluid properties on the droplet generation mechanism in a microfluidic T-junction, this paper will present supporting evidence in detail on the above and a comparison of the findings with the existing theories.

Numerical Analysis of Flare Gas Recovery Ejector

Flaring and venting contributes significantly to greenhouse gas emissions and environmental pollution in the upstream oil and gas industry. Present work focuses on a horizontal flow, multiphase ejector used for recovery of these flared gases. The ejector typically handles these gases being entrained by high pressure well head fluid and a comprehensive understanding is necessary to design and operate such recovery system. A CFD based analysis of the flow through the ejector has been reported in this paper. The flow domain was meshed and the mass and momentum equations for fluid flow were solved using commercial software CFX (v14.5). Euler-Euler multiphase approach was used to model different phases. The entrainment behavior of the ejector was investigated and compared for different fluid flow conditions. It was observed that for a fixed primary fluid flow rate, the entrained or secondary flow rate decreased linearly with an increase in pressure difference between exit and suction pressure. The higher was primary flow rate, the greater was the suction created ahead of the primary nozzle and greater was the amount of energy added to the entrained fluid.

Flow Characterization in an ESP Pump Using Conductivity Measurements

Electrical Submersible Pumps (ESPs) are used in upstream petroleum industry for pumping liquid-gas mixtures. The presence of gas in the flow reduces the efficiency of ESPs. To investigate the effect of gas in the flow medium, Electrical Resistance Tomography (ERT) is performed on the two diffuser stages in a three-stage ESP which was manufactured by Baker Hughes Company. In an ERT system, the relative conductivity of the two-phase fluid mixture in comparison with the conductivity of pure liquid is measured which is used to obtain the Gas Volume Fraction (GVF) and mixture concentration. The measured GVF and concentration is used to characterize the flow for different flow rates of water and air, inlet pressures and rotating speeds.

Study on Pressure Fluctuation and Fluctuation Reduction of a Micro Vortex Pump

With the increasing demand of small-flow and high-head pumps, vortex pump, which can be used in industry, agriculture, medical and aerospace etc., has become more and more popular as low specific pump. However, the pressure fluctuation of fluid in the vortex pump would cause flow noise and vibration which may result in damage to the equipment. Clearly, it is important to reduce the fluctuation causing by fluid flow as much as possible. This study examined and discussed the law of pressure fluctuation in a micro vortex pump by the method of numerical simulation. In addition, a random distribution method was applied to design two new impellers with different blade spacing. Moreover, the influence on pressure fluctuation of different blade positions was predicted by theoretical analysis and CFD analysis. The results show that the blade passing frequency is dominative in the pressure fluctuation. Although the average static pressure distribution on the circumference of the micro vortex pump increased gradually along inlet to outlet, the pressure pulse amplitudes were fluctuant and the maximum amplitude area was close to the stripper. Affected by the vortex motion in the pump, there were clutters in the spectrum from inlet to outlet even for the vortex pump with uniform circumferential blade spacing. The study also indicated that uneven circumferential spacing would yield additional frequency in the spectrum compared with even one and reduce the magnitude of the dominant frequency without decreasing the performance of the pump sharply. Based on the consequence, this paper proves the feasibility of applying uneven blade spacing to reduce pressure fluctuation in a vortex pump. And it could be meaningful for the noise and vibration reduction as well as development of vortex pumps.

An Experimental Investigation on the Flow Characteristics Over Dimple Arrays Pertinent to Internal Cooling of Turbine Blades

Due to the dimple’s unique characteristics of comparatively low pressure loss penalty and good heat transfer enhancement performance, dimple provides a very desirable alternative internal cooling technique for gas turbine blades. In the present study, an experimental investigation was conducted to quantify the flow characteristics over staggered dimple arrays and to examine the vortex structures inside the dimples. In addition to the surface pressure measurements, a high-resolution digital Particle Image Velocimetry (PIV) system was also utilized to achieve detailed flow field measurements to quantify the characteristics of the turbulent channel flow over the dimple arrays in terms of the ensemble-averaged velocity, Reynolds shear stress and turbulence kinetic energy (TKE) distributions. The experimental measurement results show that the friction factor of the dimpled surface is much higher than that of a flat surface. The measured pressure distribution within a dimple reveals clearly that flow separation and attachment would occur inside each dimple. In comparison with those of a conventional channel flow with flat surface, the channel flow over the dimpled arrays was found to have much stronger Reynolds stress and higher TKE level. Such unique flow characteristics are believed to be the reasons why a dimpled surface would have a better heat transfer enhancement performance for internal cooling of turbine blades as reported in those previous studies.

Simulation and Mockup of SNS Jet-Flow Target With Wall Jet for Cavitation Damage Mitigation

Pressure waves created in liquid mercury targets at the pulsed Spallation Neutron Source (SNS) at Oak Ridge National Laboratory induce cavitation damage on the stainless steel target vessel. The cavitation damage is thought to limit the lifetime of the target for power levels at and above 1 MW. Severe through-wall cavitation damage on an internal wall near the beam entrance window has been observed in spent-targets. Surprisingly though, there is very little damage on the walls that bound an annular mercury channel that wraps around the front and outside of the target. The mercury flow through this channel is characterized by smooth, attached streamlines. One theory to explain this lack of damage is that the uni-directional flow biases the direction of the collapsing cavitation bubble, reducing the impact pressure and subsequent damage. The theory has been reinforced by in-beam separate effects data. For this reason, a second-generation SNS mercury target has been designed with an internal wall jet configuration intended to protect the concave wall where damage has been observed. The wall jet mimics the annular flow channel streamlines, but since the jet is bounded on only one side, the momentum is gradually diffused by the bulk flow interactions as it progresses around the cicular path of the target nose. Numerical simulations of the flow through this jet-flow target have been completed, and a water loop has been assembled with a transparent test target in order to visualize and measure the flow field. This paper presents the wall jet simulation results, as well as early experimental data from the test loop.

Flow Measurements in a Matched-Index-of-Refraction Aortic Arch Model for Endothelial Cell Culture

Flow details such as wall shear stress, hemodynamic pressure, and separation can play an important role in the development and progression of inflammation and cardiovascular disease, such as atherosclerosis. Clinical evidence correlating blood vessel locations exhibiting atherosclerosis and plaque buildup to flow disturbances and separation is significant. Prevalence of atherosclerosis in cardiovascular patients is noticed in vessels exhibiting geometric features such as bifurcation, arching, and stenosis. The bending vessel geometry is interesting for the wealth and variety of flow physics that it incorporates. An in vitro flow loop system for the study of cardiovascular disease is described. The system incorporates an aortic arch vessel model that permits endothelial cell culturing, sampling, and imaging on the aortic lumen. The model was designed to allow imaging of the internal flow by choice of the clear model material and the optically compatible working fluid. Particle image velocimetry measurements were acquired at different locations on the arch, for time-averaged inlet Reynolds number range of 2000 to 4400. It was found that the peristaltic pump introduced significant pulsatility to the flow particularly at the low rpm. The flow behavior in the arch is discussed with emphasis on separation and recirculation zones.