bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Flow Controlling on LP Turbine at Different Reynolds Number
Authors: Chishty Muhammad Aqib , Hamdani Hossein Raza , Parvez Khalid , Qadri Muhammad Nafees Mumtaz
Published: July 2013

Active and passive techniques have been used in the past, to control flow separation. Numerous studies were published on controlling and delaying the flow separation on low pressure turbine. In this study, a single dimple (i.e. passive device) is engraved on the suction side of LP turbine cascade T106A. The main aim of this research is to find out the optimum parameters of dimple i.e. diameter (D) and depth (h) which can produce strong enough vortex that can control the flow either in transition or fully turbulent phase. Furthermore, this optimal dimple is engraved to suppress the boundary layer separation at different Reynolds number (based on the chord length and inlet velocity). The dimple of different depth and diameter are used to find the optimal depth to diameter ratio. Computational results show that the optimal ratio of depth to diameter (h/D) for dimple is 0.0845 and depth to grid boundary layer (h/δ) is 0.5152. This optimized dimple efficiently reduces the normalized loss coefficient and it is found that the negative values of shear stresses found in uncontrolled case are being removed by the dimple. After that, dimple of optimized parameters are used to suppress the laminar separation bubble at different Re∼25000, 50000 and 91000. It was noticed that the dimple did not reduce the losses at Re∼25000. But at Re∼50000, it produced such a strong vortex that reduced the normalized loss coefficient to 25%, while 5% losses were reduced at Re∼91000. It can be concluded that the optimized dimple effectively controlled flow separation and reduced normalized loss coefficient from Re 25000 to 91000. As the losses are decreased, this will increase the low pressure turbine efficiency and reduce its fuel consumption.
Development of Microbubble Generator and its Utilization to Enhance the Mass Transfer in the Bubble Plumes and Columns
Authors: Kaneko Akiko , Gong Xiaobo , Takagi Shu , Matsumoto Yoichiro
Published: July 2013

Microbubble has characteristics of large surface area to unit volume and small buoyancy. We propose an effective technique to generate tiny bubbles less than 200 μm diameter utilizing a venturi tube at high void fraction. The mechanism of bubble breakup in the venturi tube is elucidated that the bubbles expanded after passing through the throat and then shrank rapidly. The tiny bubbles are generated due to the surface instability of shrinking bubbles. The effect of bubble diameter and plume structure on mass transfer efficiency in bubble plumes and columns are investigated numerically. In order to capture the detailed plume structure, the interaction between liquid and bubbles is treated by a two-way coupling Eulerian–Lagrangian method. The gas transfer from bubbles to liquid is computed by modeling the mass transfer rate of individual bubbles. The numerical results show that the dissolution efficiency changes rapidly when the initial bubble size reaches certain value. The effect of bubble-induced liquid velocity on the residence time of microbubbles increases with the decrease of initial bubble diameters, and also increases with the reduction of initial water depth. By comparing the concentrated and uniform bubble injections, the results suggest that the uniform injection provides much better mass transfer efficiency becasue the circulation of liquid induced by bubble is greatly suppressed.
Experimental Analysis of a Bathtub Vortex in a Simplified Cowl Box of Automotive Vehicles
Authors: Recoquillon Yann , Andrès Emmanuelle , Kourta Azeddine
Published: July 2013

On automotive vehicles, the cowl box is a volume located at the bottom of the windshield, under the cowl top grille. It provides external fresh air to the HVAC (Heating, Ventilating and Air Conditioning) unit and it is used to collect water coming from the windshield under rain conditions. This box is designed as a tranquillisation chamber to segregate water from air and avoid the ingress of rainwater into the HVAC unit. However, as the area is awkward to access with measuring devices, our knowledge about the physics of flow in the cowl box is limited.

The present work aims to advance our knowledge through experimental work on the air/water flow in a simplified cowl box in order to optimize the box size and improve numerical models. This paper will focus on the analysis of the bathtub vortex, which is potentially responsible for insufficient draining of the water collected in the cowl box.

The experimental set-up consists of a Plexiglas parallelepiped representing a simplified cowl box with top cowl grille, HVAC inlet and drain. A blower generates airflow through the HVAC inlet. A water sheet, with controlled flow rate, is created on an inclined plane representing the windshield. Velocity measurements of all components are obtained by PIV (Particle Image Velocimetry) in the liquid phase and the surface level is recorded by a capacitance probe near the drain. Moreover, contour detection of the vortex core is achieved using a high-speed camera. Results show a relationship between the pressure loss generated by the airflow in the cowl box, the water level and the vortex structure. The modification of the vortex structure as well as the modification of velocity components near the air core are visible only in transient stages. These experimental results give us today some insight to understand the physical phenomena occurring in the cowl box.
Optimization of the Inlet Velocity Profile in a Conical Diffuser
Authors: Galván Sergio , Reggio Marcelo , Guibault Francois
Published: July 2013

Past numerical and experimental research has shown that the draft tube inlet velocity has a critical importance in the hydropower plants performance. However, there is a lack of information in terms of flow parameters and in particular of swirl distribution. With regards to the overall performance of a turbine, the optimization of the inlet velocity profile constitutes a new approach to control the inlet flow conditions to yield better draft tube and turbine performance. Numerical optimization methods have been successfully used for a variety of design problems. However, the optimization of boundary conditions in hydraulic turbines is a new challenge. Thus a detailed research of the optimization methodology is the aim of this paper. Three different vortex equations to represent the inlet velocity profile are applied to a cone diffuser and the behavior of the objective function is analyzed. A discussion concerning the development of a flow structure caused by the inlet swirl parameters is included.
Numerical and Experimental Investigation of Wave-Structure Interactions on Coastal Highways and Levees
Authors: Zhang Ning , Li Zhuang , Davis Alan , Li Puxuan , He Anpeng
Published: July 2013

Erosion due to storm surges and wave actions damages coastal highway and levee systems in Gulf coast. During previous hurricanes, a large portion of coastal highways were damaged by the storm surge. The damages are often on the downstream shoulder of the highways. In this study, numerical and experimental analyses were conducted to uncover the erosion-causing flow physics, which aims to improve the erosion-resistant design of coastal structures. The impacts of wave actions, especially frequency components, on the coastal structures were investigated. A test levee was built, and was placed on a Gulf beach for experiment. Real time wave action pressure data on the surface of the test levee were collected and analyzed. The frequency components of the pressure data agree with numerical simulation results. Numerically, FLUENT was used to simulate this wave-structure interaction problem.
Perspective on the Tidal Bore: Channel Taper, Friction, Building, Maximum Height, Variation, Dissipation
Authors: Graber S. David
Published: July 2013

Building upon a companion paper, the present paper addresses additional mechanisms of the tidal bore, including channel taper and friction; building, maximum height, variation, and dissipation of the bore; and standing waves. Early studies of these mechanisms are cited and discussed in historical context. Relationships developed to investigate the effects of horizontal channel taper, vertical channel taper, and channel friction agree qualitatively with and explain field observations. Building of the bore is explained, with favorable comparison of methodology with flume observations. The maximum height that the bore is capable of achieving is one of its most interesting features; this is explained in terms agreeing with experimental observation. The two forms of the jump, undular and wall-like, are discussed. The variation of the bore height as it moves into regions of greater or lesser depth is described from field observations and flume observation, and relationships derived which explain such variation. Frictional dissipation of the bore is discussed. Standing waves that occur after the tidal bore has passed are explained as a separate phenomenon.
Simulations of the Effects of Solid Particles on the Flow Instability in Detonative Combustion
Authors: Mankbadi Mina R. , Balachandar S.
Published: July 2013

We consider here the flow instability that evolves during the spontaneous release of a high pressure gas mixed with small solid particles in a spherical shock tube representing a detonative combustion. Upon the release of the particle-laden high pressure gas contained in the small sphere, a primary shock and a secondary shock are formed. Two material interfaces develop between the two shocks: one between the gas-gas, as in the classical single-phase problem. The second one is between the pure gas and the mixture of gas and solid particles. Because of the density discontinuity, Rayleigh-Taylor-type instabilities may develop for both surfaces, which are studied herein using a high-order numerical scheme. The interaction mechanisms involved can influence the instability and control the efficiency of the combustion process.
Aerodynamic Study of a Tricycle Wheel Subsystem for Drag Reduction
Authors: Driant Thomas , Remaki Lakhdar , Moreau Stéphane , Desrochers Alain , Fellouah Hachimi
Published: July 2013

This paper deals with a CFD and experimental drag analysis on an isolated rotating wheel subsystem (including its accessories: tire, suspension, A-arms and fender) of a tricycle vehicle. The main goal of the present work is to study the effect of the fender on the wheel subsystem drag and its optimization. The Star CCM+ commercial code was used for the numerical simulations. Different flow conditions were simulated and some results were validated by comparison to wind tunnel experimental results. To perform drag optimization, several aerodynamic fender shapes were designed and simulated as part of the subsystem. A drastic drag reduction up to 30.6% compared to the original wheel subsystem was achieved through numerical simulations.
Analysis of Fluid Flow in Porous Media Using the Lattice Boltzmann Method: Inertial Flow Regime
Authors: Zhao Huizhe , Nabovati Aydin , Amon Cristina H.
Published: July 2013

In this work, we use the lattice Boltzmann method to study inertial flow in three-dimensional random fibrous porous materials. In order to validate the methodology, inertial flow in two-dimensional hexagonal arrangements of circular cylinders is simulated, and the results are compared against those previously reported in the literature. The three-dimensional fibrous porous materials are then constructed by randomly placing straight cylindrical fibers inside the computational domain. Inertial effects are studied systematically for a wide range of pore Reynolds numbers in materials with porosities between 0.60 and 0.95. A previously proposed semi-empirical relation is modified to represent the inertial effects in three-dimensional fibrous materials. Three distinct regimes of constant, quadratic, and linear relations between the inverse of the permeability and pore Reynolds number are observed for both two- and three-dimensional simulations. The critical Reynolds number, beyond which the inertial effects are strong and this relation is linear, is shown to be smaller in three-dimensional simulations, when compared to the critical Reynolds number in two-dimensional simulations.
Investigation on the Droplet Formation Time With Xanthan Gum Solutions at a T-Junction
Authors: Gu Zhipeng , Liow Jong-Leng , Zhu Guofeng
Published: July 2013

Xanthan gum solutions with various concentrations were used as the dispersed phase to study the formation time for drop formation at a T-junction. Two critical concentrations (0.05 and 0.2 wt%) of xanthan gum solutions were observed resulting in three distinct regimes. The droplet diameter increased with increasing xanthan gum concentration within each regime but the transition through each critical concentration was accompanied by a significant reduction in the droplet size. Experimental results showed that the droplet formation time decreased exponentially with increasing continuous phase flow rate. It was also found that the formation time was reduced with increasing dispersed phase flow rate. Xanthan gum solutions with a higher concentration within each regime resulted in a longer formation time, and there was a decrease in the formation time at each critical concentration. The formation time consists of growth and breakup stages and the effect of xanthan gum concentration on each stage was examined.
Structural Design and Numerical Simulation of Flue-Gas Desulfurization Absorption Tower Circulating Pump
Authors: Liu Jianrui , He Xiaoke , Guo Chenxu , Wen Haigang , Gao Zhenjun
Published: July 2013

Based on the design method of great distortion and appropriate extension to pump inlet, blades of large-scale flue-gas desulphurization absorption tower circulating pump were designed to obtain more suitable blade streamline shape for fluid flow in the internal flow field, the hydro-cyclone loss and noise of pump inlet were decreased while the pump performance and efficiency were improved. An impeller clearance automatic compensation device was added to the front shroud, which ensured the pump working in high efficiency area, and the volute sections 5 through 7 were designed to be double-channel to effectively reduce the radial force. Wear of the pump was greatly reduced and the pump service life was extended by developing a new material M26-23V alloy steel. The pump internal flow field was calculated through k-ε model provided by CFD software Fluent 6.3, and the pump performance was predicted. The pump performance test results showed that the prediction performance curve was consistent with test performance curve. It can be concluded that the pump efficiency at design point reaches up to 85.3%, and the comprehensive technical index meet the design requirements. The pump service life was prolonged by rational structure design and favorable wear resistance.
Monte Carlo Simulations of Micro-Particle Detachment and Resuspension From Surfaces in Turbulent Flows
Authors: Goldasteh Iman , Ahmadi Goodarz , Ferro Andrea
Published: July 2013

Micro-particle adhesion, detachment and resuspension from surfaces have attracted considerable attention due to their numerous applications in semiconductor, xerographic, and pharmaceutical industries, and, more recently, in understanding indoor air quality. However, most earlier studies have focused on idealized spherical particles and smooth surfaces, and the effects of particle irregularities and surface roughness on the rate of particle removal and resuspension are not well understood. In this work, a Monte Carlo simulation of particle resuspension from a surface under turbulent flow conditions was developed and resuspension of nearly spherical and irregular shaped particles with rough surfaces from substrates under turbulent flow condition was studied. Following our earlier approach, compact irregular shaped particles were modeled as spherical particles with a number of hemispherical bumps. It was assumed that the bump surfaces also have fine roughness. The extended Johnson-Kendall-Roberts (JKR) adhesion theory for rough surfaces was used to model the particle adhesion and detachment.

A number of assumptions were made to apply the model. It was assumed that the particles have a Gaussian size distribution. The number of bumps of the irregular particles and surface roughness values of particle are assumed to be random, respectively, with Poisson and log-normal distributions. For particle detachment from the surface, the theory of critical moment was used. The effects of particle size, turbulent flow, particle irregularity and surface roughness on particle detachment and resuspension were studied for different cases. The Monte Carlo model predictions show probabilistic distributions of the particle resuspension. The simulation results are compared with the available experimental data and good agreement was found. The study provided information on the random nature of particle resuspension due to the randomness in the airflow, particle size distribution and surface roughness.
Numerical Investigation of Viscous Flow in Three Centrifugal Pumps
Authors: Moreno Carlos Luis , Fuenmayor Alejandro , Núñez Gilberto , De Andrade Jesús , Noguera Ricardo , Asuaje Miguel
Published: July 2013

Centrifugal pump performance is affected when pumping viscous liquids, requiring a larger power input than the same pump handling water. In applications of chemical, civil, environmental, and mechanical engineering that involve centrifugal pumps, it is a challenge to accurately estimate and even more of a challenge to improve their performance when handling viscous liquids. When accurate performance data is needed, difficult experiments must be conducted with the operating viscous flow. The extension of the applicability of numerical techniques for solving fluid dynamics (CFD) permits the consideration of these tools as a definite possibility for predicting the performance of centrifugal pumps with viscous flows. The purpose of this study is to perform a 3D-CFD steady-state simulation of three different configurations of centrifugal pumps. The first is an impeller-diffuser pump (ns = 19) taken from an ESP model. The second is a Francis Pump-Turbine (ns = 28). Finally, the third configuration possesses an impeller and volute (ns = 32). The objective is to characterize and evaluate their performances with four different fluids from 1 to 420 cSt. These are: water at 25°C, SAE10 and SAE30 oils, and Fuel Oil Medium (FOM). For water flow conditions, the numerical results were compared with experimental data, and found to be consistent with global performance parameters. With regard to the higher viscosity fluids, the CFD calculation was compared with those obtained through the standard empirical method (ANSI/HI9.6.7). This resulted in good agreement between the performance results. The commercial software ANSYS-CFX was used for the CFD calculations.

The resulting pump performance curve (head, hydraulic efficiency and power output) is consistent with that expected by theory. In general, as the viscosity of fluids increases, the hydraulic energy losses increase. Of the three pumps, slip factor for SAE30 oil was larger for all volumetric flows since it features the best guidance of the flow in the impeller blade passage. For the ns32 pump and the pump-turbine ns28, the volute losses rose from water to FOM, just like the impeller hydraulic losses. For these two turbo machines, the impeller losses were larger than volute losses. For the pumps with volute, the effects of fluid viscosity on the radial forces were evaluated. It was found that the radial forces decrease when the viscosity increases. This paper attempts to contribute to a better understanding of fluid dynamics within centrifugal pump impellers handling viscous fluids, and intends to shed more light on the approaches that performance prediction models should follow in the future.
The Optimization of Flow-Induced Noise Under BPF by Changing the Impeller Diameter
Authors: Yang Jun , Yuan Shouqi , Yuan Jianping , Li Yaling , Si Qiaorui
Published: July 2013

With the widely application of IS series centrifugal pumps in industry and agriculture, the blade-passing frequency (BPF) flow-induced noise in these pumps are tend to be optimized. In this paper, a common type IS50-65-160 is chosen as the model pump to do the optimization of BPF noise. Considering both the effect of noise reduction and applicability of the project, an optimization scheme of cutting the impeller diameter is proposed. An analysis of the different performance curves, corresponding to different impeller diameters, emerges the diameter optimization range of impeller from 0.95Dd to 1.0Dd. And two optimal schemes, cutting impeller diameter by 2.5% and 5%, are taken through the comparison with experimental results. Then properties of this BPF noise are predicted by a hybrid method through ANSYS-CFX and LMS Virtual. Lab Acoustics. The result shows that the dipole source is the main flow-induced noise in low specific speed pump, so only dipole source is considered in the simulation. And the sound pressure distributions on monitoring points of these two suggested schemes are calculated and compared with the design impeller. The comparison shows that the optimal scheme is to cut the impeller diameter by 2.5%, while a further cut (0.975Dd) would lead to a much greater loss in head and the noise control effect is not better than cutting by 2.5%.
Evaluation of a Twin Screw Pump for Use in High Gas Volume Fraction Flows
Authors: Morrison Gerald L. , Patil Abhay , Cihak Daniel
Published: July 2013

The use of multiphase pumps on gas and oil wells which have Gas Volume Fractions (GVF) between 50 and 100% have been shown to have practical applications[1]. A single multiphase pump can replace a separation system, gas compressor, and liquid pump. This can significantly reduce installation cost, maintenance cost, and the space occupied by the system. By reducing the well head pressure, additional production can also be obtained. This work investigates the ability of a 200 hp, 635 gpm twin screw pump designed for use as a multiphase pump to operate over a range of gas volume fractions, inlet pressure, pressure rise, and operating speed. GVF’s from 50% to 100% are considered with inlet pressures from 15 to 100 psig. The pump pressure rise is varied from 50 to 300 psig for operating speeds of 900, 1350, and 1800 rpm. The working fluids for this evaluation are air and water. Each are separately measured prior to injection into the pump inlet. Electrical power consumed along with pressure and temperature measurements across the pump allow the evaluation of pump efficiency, hydraulic performance, volumetric efficiency, and effectiveness (reduction in hydraulic efficiency from pure liquid performance).
Blade Outlet Angle Effect on Two-Phase Flow in Chemical Pump With Crystallization Phenomenon
Authors: Liu Dong , Li Zhong , Wang Chun-lin , Yang Min-guan
Published: July 2013

Particle Image Velocimetry combined with image processing method is used to measure the liquid-solid two phase flows with crystallization phenomenon in three different impellers. The experimental results indicate that: there is not any crystal particle during the delay period, and the performance of pump is not affected. After the delay period, the crystal nuclei are born from the supersaturating solution and growing larger with temperature decreasing. And it was found solid particles tend to move towards blade pressure surface. It is also observed that collision between solid particles with tail part of blade pressure surface is more intensive in impeller with large blade outlet angle.
Optimal Perturbations in Boundary Layer Flows Over Rough Surfaces
Authors: Cherubini S. , de Tullio M. D. , De Palma P. , Pascazio G.
Published: July 2013

This work provides a three-dimensional energy optimization analysis, looking for perturbations inducing the largest energy growth at a finite time in a boundary-layer flow in the presence of roughness elements. Amplification mechanisms are described which by-pass the asymptotical growth of Tollmien–Schlichting waves. The immersed boundary technique has been coupled with a Lagrangian optimization in a three-dimensional framework. Two types of roughness elements have been studied, characterized by a different height. The results show that even very small roughness elements, inducing only a weak deformation of the base flow, can strongly localize the optimal disturbance. Moreover, the highest value of the energy gain is obtained for a varicose perturbation, pointing out the importance of varicose instabilities for such a flow and a different behavior with respect to the secondary instability theory of boundary layer streaks.
Control of the Flow Direction Induced by Plasma Actuator
Authors: Ikoshi Yu , Ogata Satoshi , Segawa Takehiko , Yamatani Ryota
Published: July 2013

It is known that a dielectric barrier discharge plasma actuator (DBD-PA) induces tangential flow in the vicinity of the wall. In the conventional studies the induced flow was generated in the direction from the upper electrode to the lower electrode. The direction of the induced flow was one-way using DBD-PA composed of asymmetric electrodes. However, in this experiment, it was found that the flow induced by DBD-PA can be generated in the opposite direction in contrast with conventional results. In this study, effects of DBD induced flow on applied voltage characteristics were investigated by means of PIV analysis. When square wave voltages biased negative are applied to the electrodes of DBD-PA, the flow is generated in the direction from the lower electrode to the upper electrode. It should be noted that it is not reversed by sine waves even with same amplitudes and frequencies when the reverse flow was generated by DBD-PA, a vortex is induced above the area of plasma. The vortex height was about 10 mm, and it tended to change slightly its shape based on the electrode width. It seems that the vortex on the plasma area play an important role in the mechanism of the reverse flow. The plasma actuator has been focused as an actuator for aerodynamic flow control. If it becomes possible to control the flow direction as well as the velocity by changing the applied voltage, the applications of the plasma actuator can be spread across a wide area of industry.
Use of Lattice-Boltzmann Method in Mass Transfer for the Wall Shear Stress Calculation in an Unsteady Laminar Flow Downstream of a Cylinder Located in a 2D Rectangular Channel
Authors: Abassi Wafik , Aloui Fethi , Ben Nasrallah Sassi , Legrand Jack
Published: July 2013

A Lattice Boltzmann method (LBM) is proposed to study the flow and mass transfer in the parietal zone of a channel containing a blocking circular obstacle at low Reynolds number. For such configuration, the variation of Re based on cylinder diameter leads to different regime that fluid may occur during it flowing. Hence, this varied behaviour of flow downstream of the obstacle affects the mass transfer rate in the parietal zone of the channel.

A sensor with zero concentration on the surface is placed at different locations on the channel wall downstream of the cylinder. Flow velocity and concentration profile of diffusing species on the sensor were evaluated and analyzed for different Reynolds. The Sherwood numbers are calculated and compared with available experimental data.

For the present simulation, LBM is based on the D2Q9 lattice model and the single relaxation time approach called BGK method.

The challenge of this work is to extend the use of the mesoscopic method (LBM) for a flow problem to studying the enhancement of the rate of mass transfer to channel wall downstream of the obstacle. The numerical results are in good agreement with the benchmark result available in the literature. The highlight of calculation is the flexibility to deal with the boundary conditions for such a problem.

The result indicates that LBM is useful for simulation of fluid flows with mass transfer as well as heat transfer.
On the Stability of Taylor - Couette Flow With Axial Flow
Authors: Berrich Emna , Aloui Fethi , Legrand Jack
Published: July 2013

An experimental investigation of Taylor-Couette flows with axial flow is presented. Two techniques are used: Visualization using the Kalliroscope and Electro-diffusion method using electrochemical probes. The fluid is confined between concentric cylinders. It is constituted by an electrochemical solution seeding with 2% of a rheoscopic liquid AQ-1000 (Kalliroscope Corp., U.S.A.). The rheoscopic liquid contains small particles reflecting light in dependence on their orientation imposed by the flow direction. The reflected light intensity of Kalliroscope flakes allows a qualitative study of the flow. While the polarography technique allows the measurement of diffusion limit current intensities delivered by the electrochemical probes. The frequency responses of the probe to the flow allow the determination of the instantaneous and local mass transfer and the instantaneous wall shear rate.

Two protocols were adopted to study the effect of an axial flow superposed to Couette-Taylor flows and the history flow effect. The first one consists to impose an azimuthal flow to the inner cylinder. When the regime was established, we superposed the axial flow. This protocol was named “the direct protocol”. While the second protocol consists to impose firstly the axial flow on the gap of the system then the azimuthal flow. We named it “the inverse protocol”. We demonstrated that the Couette-Taylor flow with axial flow is strongly dependent on the flow history (the protocol). For the same Taylor number and axial Reynolds number, the resulting flow is completely different. An axial flow superposed to Couette-Taylor flow can delay the instabilities apparition; generate the displacement of the Taylor vortices in the same direction as the axial flow or in the opposite direction; and modify the instability character of the flow by developing helical vortices or wavy helical vortices.
Ultrasonic Measurement of Multiphase Flow Erosion Patterns in a Standard Elbow
Authors: Kesana N. R. , Grubb S. A. , McLaury B. S. , Shirazi S. A.
Published: July 2013

Solid particle erosion is a mechanical process in which material is removed from a surface due to impacts of solid particles transported within a fluid. It is a common problem faced by the petroleum industry, as solid particles are also produced along with oil and gas. The erosion not only causes economic losses resulting from repairs and decreased production but also causes safety and environmental concerns. Therefore, the metal losses occurring in different multiphase flow regimes need to be studied and understood in order to develop protective guidelines for oil and gas production equipment. In the current study, a novel non-invasive ultrasonic (UT) device has been developed and implemented to measure the metal loss at 16 different locations inside an elbow. Initially, experiments were performed with a single-phase carrier fluid (gas-sand) moving in the pipeline, and the erosion magnitudes are compared with Computational Fluid Dynamics (CFD) results and found to be in good agreement. Next, experiments were extended to the multiphase slug flow regime. Influence of particle diameter and liquid viscosity were also studied. Two different particle sizes (150 and 300 micron sand) were used for performing tests. The shapes of the sand are also different with the 300 micron sand being sharper than the 150 micron sand. Three different liquid viscosities were used for the present study (1 cP, 10 cP and 40 cP). Carboxymethyl Cellulose (CMC) was used to increase the viscosity of the liquid without significantly altering the density of the liquid. While performing the UT experiments, simultaneous metal loss measurements were also made using an intrusive Electrical Resistance (ER) probe in a section of straight pipe. The probe in the straight pipe is an angle-head probe which protrudes into the flow with the face placed in the center of the pipe. The UT erosion measurements in a bend are also compared with experimental data obtained placing an intrusive flat head ER probe flush in a bend, and the results were found to be in good agreement. Finally, the non-invasive NanoUT permanent placement temperature compensated ultrasonic wall thickness device developed for this work has the capability of measuring metal loss at many locations and also identifying the maximum erosive location on the pipe bend.
Optimization of a Stirling Engine Performances: A Study Based on Experiments Design Approach
Authors: Gheith Ramla , Aloui Fethi , Ben Nasrallah Sassi
Published: July 2013

The Stirling engine performances depend on several physicals characteristics and functioning parameters. The experimental design is an alternative to identify the parameters sets allowing optimal Stirling engine performances. So, a four factor Central Composite Rotatable Design (CCRD) was used to observe the effect of cooling water flowrate, initial charge pressure, heating temperature, and operation time on a Stirling engine brake power. The influence of each parameter and the effect of the interaction between two or three parameters on the engine performances are presented and analyzed. With modeling, optimal conditions for the Stirling engine functioning are the following: charge pressure of 8 bar, heating temperature of 500 °C and cooling water flow rates of 7.34 l/mn, independently of the engine operation time.
Approach to Prevent Spurious Oscillations in Compressible Multicomponent Flows Using High-Order Methods
Authors: Terashima Hiroshi , Kawai Soshi , Koshi Mitsuo
Published: July 2013

We present an interface-capturing method for fluid interfaces in compressible multicomponent flows using high-order central-difference-based schemes. Numerical diffusion terms are consistently designed so that the velocity, pressure, and temperature equilibriums are maintained at the fluid interfaces, while serving as an efficient interface-capturing. Advection problems of a contact discontinuity and a material interface shows that 1) the present method maintains the velocity, pressure, and temperature equilibriums at the fluid interfaces (oscillation-free property) and 2) the numerical diffusion terms effectively works for suppressing spurious wiggles of the density or temperature. Comparisons with a conventional fully-conservative approach demonstrates the superiority of the present method in avoiding spurious oscillations. A shock tube problem of two-component gases shows the capability for capturing the shock wave while the velocity and pressure equilibriums are successfully maintained at the contact discontinuity.
Calibration of the NASA GRC 16″ Mass-Flow Plug
Authors: Davis David O. , Friedlander David J. , Saunders J. David , Frate Franco C. , Foster Lancert E.
Published: July 2013

The results of an experimental calibration of the NASA Glenn Research Center 16″ Mass-Flow Plug (MFP) are presented and compared to a previously obtained calibration of a 15″ Mass-Flow Plug. An ASME low-beta, long-radius nozzle was used as the calibration reference. The discharge coefficient for the ASME nozzle was obtained by numerically simulating the flow through the nozzle from the WIND-US code. The results showed agreement between the 15″ and 16″ MFPs for area ratios (MFP to pipe area ratio) greater than 0.6 but deviate at area ratios below this value for reasons that are not fully understood. A general uncertainty analysis was also performed and indicates that large uncertainties in the calibration are present for low MFP area ratios.
Assessment of the Degree of Mixing in Microchannel Two-Fluid Flows
Authors: Manickam Vijaymaran , Celik Ismail B. , Mason Jerry , Liu Yuxin
Published: July 2013

Microchannels are used for delivery of two-or more fluids for multiple purposes, such as drug delivery, where good mixing is desired in a very short time (or distance). For this purpose, many design options are being proposed in the literature. For example herringbone baffles at the bottom of a rectangular channel are proposed to enhance mixing in a drug delivery device [6]. To assess the effectiveness of such devices many experiments need to be performed thus reducing the design cycle time and the cost involved. Computational fluid dynamics (CFD) can and is being used to shorten this design cycle by performing parametric analysis; however, due to numerical errors it is also necessary to verify and then validate the numerical models to ensure that the predictions are indeed accurate. In this study a recently developed microchannel presently in use is analyzed using CFD to determine its mixing efficiency. There are two common ways of assessing the degree of mixing: (a) via calculation of a passive scalar transport equation, (b) by following fluid particle trajectories and calculating the statistics. The first approach suffers from high degree of numerical diffusion. The second approach is usually used to only obtain qualitative information rather than quantitative assessment. In this study we explore both approaches and reconcile both of these in terms of extracting quantitative information. Furthermore we assess the results of simulations using both approaches to determine a mixing index that provides directly a measure of the extent of mixing.
A Nonlinear Computational Model for Floating Wind Turbines
Authors: Nematbakhsh Ali , Olinger David J. , Tryggvason Gretar
Published: July 2013

The dynamic motion of floating wind turbines is studied using computational simulations. The full three-dimensional Navier-Stokes equations are solved on a regular structured grid, using a level set method for the free surface and modified immersed boundary method to model the turbine platform. The tethers, the tower, the nacelle and the rotor weight are include using reduced order dynamic models, resulting in an efficient numerical approach. Wind is modeled as a constant thrust force. Other aerodynamic loading, rotor gyroscopic effects, and aeroelastic effects are not considered in the current study. The response of a tension leg platform to moderate amplitude waves is examined. By using the current approach, nearly all the nonlinear and viscose effects can be considered while keeping the computational cost reasonable. The model is applied to a Tension Leg Platform (TLP) consisting of a ballasted cylindrical tank.
A Practical Approach to Speed Up NPSHr Prediction of Centrifugal Pumps Using CFD Cavitation Model
Authors: Ding H. , Visser F. C. , Jiang Y.
Published: July 2013

This paper presents an innovative NPSHr prediction procedure. Derived through analyzing the definition of NPSHr and the characteristics of pump head vs. NPSH curve (i.e. head drop curve), this procedure can significantly reduce the number of simulations needed in NPSHr prediction. For the majority of cases, NPSHr can be predicted with reasonable accuracy for one flow rate in as little as three simulation runs. This procedure is also very robust since it can avoid running simulations under severe cavitation conditions. Therefore simulation convergence is improved and simulation time is reduced for each simulation step.

In the paper, the methodology of the proposed approach is derived and explained. The complete procedure with suggested strategies is laid out in detail. Then the procedure is demonstrated against an industrial pump case. NPSHr prediction results are compared with experimental data. Important factors which can affect NPSHr prediction are also indentified and discussed.
Investigation of the Turbulent Flow Behaviour in a Transpired Air Collector
Authors: Greig David , Siddiqui Kamran , Karava Panagiota
Published: July 2013

There is an increasing interest in developing renewable energy systems to address the increasing global energy demand and fight climate change. One emerging technology is the transpired air collector, which is a unique type of corrugated and perforated sheet metal installed in front of a building to absorb incident sunlight to preheat the building air intake. As the airflow behaviour in the channel influences the air heat gain, it is important to understand the fluid dynamics within the transpired air collector to maximize its efficiency. A full scale experimental setup using a commercial transpired air collector was built in a laboratory environment. Particle Image Velocimetry (PIV) was used to measure two-dimensional velocity fields at different air flow rates and at different locations inside the channel. PIV data were used to compute various turbulent characteristics of the air flow. It was found that the mean velocity peaks tended towards the flat construction wall side. The profiles of the Reynolds stress indicated a significant momentum transfer from the corrugation wall by the turbulent velocity field towards the bulk flow. Results demonstrate that the turbulence produced by the corrugation waveform dominates the entire channel.
An Experimental Study on the Effects of Wake Interference on the Performances of Wind Turbines Over Complex Terrains
Authors: Hu Hui , Ozbay Ahmet , Tian Wei , Yang Zifeng
Published: July 2013

An experimental study was conducted to investigate the interferences of wind turbines sited over hilly terrains in order to elucidate underlying physics to explore/optimize design paradigms of wind turbines sited over complex terrains for higher power yield and better durability. The experiments were conducted in a large wind tunnel with of wind turbine models sited over a flat terrain (baseline case) and a 2D-ridge with non-homogenous atmospheric boundary layer winds. In addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the wind turbine models, a high-resolution digital Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the flow characteristics of the surface winds and wake interferences among multiple wind turbines over flat (baseline case) and complex terrains. The detailed flow field measurements were correlated with the wind load measurements and power outputs of the wind turbine models to elucidate the underlying physics associated with turbine power generation and fatigue loads acting on the wind turbines.
Compressible Euler Extension of a Massively-Parallel Spectral Element Solver
Authors: Camp Joshua L. , Duggleby Andrew
Published: July 2013

Current supercomputing systems have tens or hundreds of thousands of cores and are trending to GPU and co-compute platforms that deliver thousands of cores per node. Modern computational fluid dynamics codes must be designed to take advantage of these developments in order to further their use in the design cycle. Furthermore, these codes must be highly accurate, stable, and geometrically flexible. NEK5000 is a massively-parallel spectral element code that exhibits these characteristics but currently only for incompressible and low-Mach flows. Adding capabilities for NEK5000 to solve the fully compressible Navier-Stokes equations will extend its usefulness to aerospace applications. As a first step the following work extends NEK5000’s capabilities to solve the 2D compressible Euler equations. Using the conservative formulation, the equations are discretized using a non-staggered spectral element mesh, and the state variables are advanced using 1st order explicit Euler time stepping. A channel with a 10% bump is used as a test case for the modification. The modified NEK5000 code performs very well despite not being optimized for use in hyperbolic equations.
Assessment of the Hydrodynamic Boundary Condition at Open-Porous Interface Using Pore-Level Flow Simulations
Authors: Nabovati Aydin , Amon Cristina H.
Published: July 2013

In this paper, we follow the pore-level flow simulation approach to investigate fluid flow over an open-porous interface using the lattice Boltzmann method. As this approach does not require any specific treatment for the interface, its results can be used to evaluate the current macroscopic boundary conditions for the interface. The Beavers & Joseph boundary condition is evaluated and the value of slip coefficient is presented as a function of porosity of the porous region. Analytical solution of the velocity profile in the close vicinity of the interface is used to predict the penetration depth. The predicted numerical results for porous penetration depth are in excellent agreement with those predicted from the analytical solution.
Understanding the 3-D Volumetric Flow and Coherent Structure Alignment in the Inner Part of a Rough Channel Using Microscopic Holography
Authors: Talapatra Siddharth , Katz Joseph
Published: July 2013

The 3D flow in the inner part of a turbulent boundary layer over a rough surface, with Reτ = 3400, is measured using digital in-line microscopic holography and particle tracking. Experiments are performed in a special facility, in which the optical refractive index of the transparent rough wall is matched with that of the working fluid. Holograms are recorded in a sample volume covering the roughness sublayer. Using localized particle injection, each hologram pair contains 5000–10,000 matched particle traces, providing the 3D velocity field. Profiles of mean velocity are compared to 2D PIV data, recorded under the same flow conditions. Sample instantaneous flow realizations elucidate some of the typical vortical structures encountered in the sublayer, such as low-lying vortices, some with spanwise and others with roughness groove parallel orientations, and quasi-streamwise structures with vertical inclinations of 50°–60°, some of which extend from the surface to the top of the sublayer. Conditional sampling indicates that characteristic structures have a preferred alignment in the spanwise direction close to the wall. However, with increasing elevation, these structures turn towards the streamwise direction due to roughness-induced flow channeling, and then rise in sharp angles of about 55° to the mean flow.
Predicting Bubble Migration due to Bjerknes Force in a Complex 3D Geometry: Numerical and Experimental Results
Authors: Valentin Francisco I. , Cancelos Silvina
Published: July 2013

While the Bjerknes force is not the only force experienced by a bubble subjected to an acoustic field; studies of bubble translation in non-flowing fluid have identified Bjerknes force as being the most influential. Therefore, Bjerknes force can be used to trap bubbles in predefined locations of maximum and minimum absolute pressure. Specifically challenging is to determine these locations in complex geometries because direct measurement of the acoustic pressure for the whole system is generally not possible. The objective of this research is to numerically predict Bjerknes force effect on bubble migration and accumulation in a complex 3D geometry that includes piezoelectric materials, elastic materials and a fluid media.

A numerical solution of the acoustic pressure field was obtained for this geometry, valid in the range of small pressure oscillations. Additionally, using the linearized Rayleigh-Plesset equation, which gives the volumetric oscillations of a bubble subjected to an acoustic field, the Bjerknes force was numerically computed. By knowing the Bjerknes force, a bubble migration pattern upon entering the system was predicted. A CMOS high speed camera was used to experimentally monitor bubble multimode excitation and bubble response to a stationary pressure field validating our numerical results. Results are presented for experiments conducted for a 1mm bubble diameter with acoustic fields ranging from 7 to 10 kHz which correspond to values of the structure and/or the bubble’s resonant frequency.