bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the ‘Friction Factor Jump’ Phenomenon in Hole-Pattern Seals
Authors: Sekaran Aarthi , Morrison Gerald
Published: December 2013

Hole-pattern and honeycomb seals are used to replace labyrinth seals in turbomachinery that are experiencing vibration problems, such as high pressure gas compressors. Computer simulations used to investigate the stability of a rotordynamic system require information about the stiffness, damping, and added mass generated by bearings and seals. These codes typically use bulk flow models for the fluid flow inside the bearings and seals which require empirical information about how the friction factor and leakage rate vary with rotor speed and pressure drop across the seal. Historically, experimental facilities were constructed to provide empirical data which were then used in the rotordynamic models. Ha et al (1992) observed a sudden change in the flow rate and resulting friction factor in a honeycomb seal as the pressure differential across the seal increased. This ‘friction factor jump’ was attributed to the shear flow over a seal cavity changing from a dominant normal mode to a dominant feedback mode. This was confirmed through pressure spectra showing that indeed, the shear layer instability mode changed and the frequencies present compared to predicted values. A similar effect has recently been observed in hole-pattern seals operating at high pressures, 84 bar (1200 psi). However, the pressure fluctuation spectra did not confirm the same mode change observed by Ha. The friction factor changed a by factor of around three in this instance which can drastically change the stability of the rotating system. This high pressure flow has a higher Reynolds number due to the high pressures which may explain the difference. An experimental investigation has confirmed the presence of the “friction factor jump” and that there is a change in the pressure fluctuation spectra. Further experimental investigation coupled with Large Eddy Simulation (LES) of the flow field have confirmed there is a change in the shear layer over the cavity but not the same as observed by Ha. Comparisons between the experimental and computational results are made along with an explanation of the flow phenomena.
Topology Optimization for Stokes Problem Under Multiple Flow Cases Using an Improved Level Set Method
Authors: Zhang Bin , Liu Xiaomin , Sun Jinju
Published: December 2013

We present a topology optimization method for the Stokes problem under multiple flow cases by an improved level set method. In the framework of level set method, an implicit reinitialization approach is developed by deriving a new formula for the smoothing parameter in the conventional reinitialization equation. And a spline-free parameterization re-meshing method is adopted to overcome the convergence difficulty in flow analysis and guarantee the direct loading of the no-slip boundary condition. The topology optimization method developed in this paper is used to implement the optimal design for Stokes flow with the different boundary conditions. Numerical examples demonstrate that the proposed approach is effective and robust for the topology optimization of Stokes problem under multiple flow cases.
The Impacts of Confined Disposal Facilities on Calcasieu Ship Channel Sedimentation
Authors: Zhang Ning , He Anpeng , Corbino Jeff , Schroeder Paul , Bolton Johnathan
Published: December 2013

The confined disposal facilities (CDFs) are the areas along Calcasieu Ship Channel to store dredged sediments from the ship channel. As the sediments settle in the CDFs, the low concentration sediment flows are discharged into the open water adjacent to the CDFs. The paper demonstrates flow and sediment transport characteristics in the open water due to the CDF discharge. The sediment distributions in all three dimensions in the water are revealed. The lake current effects were also investigated. A commercial CFD package ANSYS-FLUENT is used to simulate all cases in this study.
Investigation of the Interaction of Vortex Rings and Thin Porous Screens Using Molecular Tagging Velocimetry (MTV)
Authors: Hrynuk John , Bohl Douglas
Published: December 2013

The interaction of a single travelling vortex ring with thin permeable screens of constant porosity is investigated. Molecular Tagging Velocimetry (MTV), a non-invasive flow field measurement technique, is used to quantify the velocity field. The resulting velocity field is remapped onto a regularly spaced grid and other flow properties, such as vorticity, are calculated. Vortex structures, including those formed in the interaction process, are tracked using the location of peak vorticity. The role of vortex shedding in the interaction process is investigated. The formation mechanism of the vorticity in the downstream vortex structure is found to be a function of boundary layer dynamics. This work extends and confirms the results of prior studies of the interaction.
Effects of Adding a Central Groove to the Squeeze Film Damper Lands
Authors: Boppa Praneetha , Sekaran Aarthi , Morrison Gerald
Published: December 2013

Squeeze film dampers (SFDs) are used in the high speed turbo machinery industry and aerospace industry as a means to reduce vibration amplitude, to provide damping, to improve dynamic stability of the rotor bearing system and to isolate structural components. Past studies have not included effects of variation of the stator geometries in a squeeze film damper. A central groove added to the squeeze film land is hypothesized to provide a uniform flow source which theory predicts will result in forces less than one fourth of that seen in SFDs without a central groove. In the present study, 3D numerical simulations of SFDs with different size central grooves on the squeeze film land are performed to predict the variation of the dynamic pressure profiles. The numerical model and method have been validated via comparison to experimental data for a SFD without a central groove. When a central groove is added to the squeeze film land, the pressures generated are reduced to half of that generated when run without a central groove on the land. The amount of reduction in pressure values depends on the volume of the groove, not on the aspect ratio of the groove. Addition of a central groove reduces the pressures, rigidity developed in squeeze film land, and forces generated by squeeze film damper.
Validation Study on Forced and Mixed Convection in the Rotatable Buoyancy Tunnel
Authors: Lance Blake W. , Harris Jeff R. , Iverson Jared M. , Spall Robert E. , Johnson Richard W. , Smith Barton L.
Published: December 2013

The Rotatable Buoyancy Tunnel (RoBuT) at Utah State University, built for validation measurements incorporating a high level of data completeness, is described along with the results from validation data sets for forced and mixed convection. One wall of the tunnel test section is heated while the other three are transparent for optical access. All boundary conditions, including geometry, wall temperature and inflow temperature and velocity, are measured and their uncertainties are reported. The tunnel’s design is unique in that the test section can be inverted by rotating the entire facility to generate mixed convection with either buoyancy aided or buoyancy opposed flow. The RoBuT can also produce forced or natural convection, either steady or transient.

Measurements for forced and buoyancy-aided mixed convection over a vertical heated plate are described. The RoBuT allows for simultaneous measurements of velocity, wall and inlet air temperature, heat flux measurements on the heated wall, and pressure drop across the test section. The fluid velocity is measured by time-averaged particle image velocimetry (PIV). The first validation case is forced convection since this flow is well understood. Both forced and mixed convection results are compared to published correlations and computational fluid dynamics (CFD) studies. The CFD is steady and 3-D using as-built measurements of the geometry. Experimental wall and inlet temperatures are used for CFD boundary conditions, as well as the inlet velocity and turbulence profiles. Three research groups perform simulations with varying levels of knowledge of the experimental results.
CFD Simulation of Large Dust Collection Cyclones Positioned Vertically in Staggered Downward Cascade Arrangement
Authors: Cristea Eugen-Dan , Conti Pierangelo
Published: December 2013

Three dimensional, time dependent Euler-Euler simulation approach for numerical calculation of multiphase strongly swirling turbulent gas-heavy laden particulate flow in large industrial collection cyclones, positioned vertically, in staggered downward cascade arrangement has been performed. The multiphase flow was featured high mass loading. This paper specifically addresses a CFD modeling of a “suspension preheater”, typical equipment for dry process cement kiln. Big sized cyclone separator is a key component of this device. The simulation case study was developed in the frame of the commercial general-purpose code ANSYS-Fluent R13. In cyclone separators the swirling gas motion induces a centrifugal force on the solid particulate phase which is the driving force behind the separation process. The turbulence disperses the solid particulates and enhances the probability that particles are discharged, as reject. Both phenomena are related to solid phase particle size distribution (PSD) and flow pattern into the collection cyclones. The multiphase turbulence was modeled using the RSM Mixture Turbulence Model. The simulation results were validated against industrial measurements carried out on an industrial suspension preheater, in the frame of heat and mass balance of cement kiln energy audit. The numerical simulation results were found in reasonable agreement with the collected industrial measurements. This CFD simulation represents a powerful engineering tool on behalf of the cement process engineer either for new cutting-edge design or for performance verification of an existing plant.
Comparison of Carotid Bifurcation Hemodynamics in Patient-Specific Geometries at Rest and During Exercise
Authors: Hewlin Rodward L. , Kizito John P.
Published: December 2013

The ultimate goal of the present study is to determine whether investigations of flow patterns (flow reversal and flow branching) and mechanical factors (wall shear stress and normal stress) have a role in local risk factors and if flow modeling can truly rely on surrogate geometric sites (simplified geometries). Cardiovascular disease is considered to be the leading cause of morbidity and mortality across the world and improved methods of disease management are desperately needed. One of the main forms of cardiovascular disease is atherosclerosis. The presence of atherosclerotic plaques has been shown to be closely related to arterial vessel geometry and hemodynamic flow patterns. Computational fluid dynamic simulations were performed on 3 carotid bifurcation arteries to demonstrate that hemodynamic factors are significant determinants for the development of vascular pathology. Relationships between disturbed flow and various geometric factors from rest-state and exercise were examined. Wall shear stress, normal stress, and vorticity were used to verify the role of age, gender, and geometry on hemodynamic flow patterns.
Computational Fluid Dynamics (CFD) Analysis of a Single-Stage Downhole Turbine
Authors: Satti Rajani , Pillalamarri Narasimha Rao , Scholz Eckard
Published: December 2013

In this study, the application of computational fluid dynamics (CFD) is explored to predict the performance characteristics in a typical single-stage downhole turbine. The single-stage turbine model utilized for this study consists of a stator and a rotor. A finite-volume based CFD approach was implemented to simulate the complex flow field around the turbine. The analysis is based on transient, three-dimensional, isothermal turbulent flow in an incompressible fluid system. The inlet flow rates and angular velocity of the rotor were varied to encompass the operating regime.

Comparison with experimental data revealed excellent agreement, proving reliability of the model in predicting the performance characteristics. Motivated by the successful model validation, a parametric study (considering blade tip clearance and blade count) was also conducted to understand the effects of the design parameters on the performance of the turbine. Detailed flow visualizations and efficiency calculations were also done to provide further insight into the overall performance of the turbine. As part of the present study, significant efforts were also spent in the following areas: standardization of CFD methodology and assessment of commercial software to develop an integrated CFD-driven design process.
A Numerical Investigation of Multi-Staged Tesla Valves
Authors: Thompson Scott M. , Walters D. Keith , Paudel Basil J. , Jamal Tausif
Published: December 2013

The Tesla valve is a passive-type check valve used for flow control/rectification in a variety of micro/mini-channel systems. Previous studies have focused on its optimal design and effectiveness (i.e. diodicity) for the low-Reynolds number regime (Re < 500). Using three-dimensional (3D) CFD, multiple, identically-shaped Tesla valves arranged in-series, i.e.: a Tesla “tree” or multi-staged Tesla valve (MSTV), were investigated. Fully-developed flow at the inlet and complete-laminar conditions throughout the entire valve structure were imposed on all numerical simulations. The number of Tesla valves, valve-to-valve distance and Reynolds number were varied to determine their effect on MSTV diodicity. The individual Tesla valves within each MSTV possessed pre-optimized design parameters as reported from the literature. Results clearly indicate that the MSTV can provide for a significantly higher diodicity than a single Tesla valve and that this MSTV diodicity increases with Reynolds number. Minimizing the distance between adjacent Tesla valves can significantly increase the MSTV diodicity and, for very low Reynolds number (Re < 50), the MSTV diodicity is near-independent of valve-to-valve distance and number of valves used. In general, more Tesla valves are required to maximize the MSTV diodicity as the Reynolds number increases. The current investigation also demonstrates that 3D numerical simulations more accurately predict the diodicity of a single Tesla valve over a wider range of Reynolds numbers.
Microfluidic Based Biosensor for Detection of Cardiac Markers
Authors: Gunda Naga Siva Kumar , Mitra Sushanta K.
Published: December 2013

Myocardial Infarction (MI) occurs when the blood flow to the heart is blocked. It is major threat to human kind. Current laboratory and ELISA tests are expensive, time consuming, and are not very sensitive. Biosensors can play an important role in the diagnosis of MI without relying on hospital visits. Therefore, researchers are focusing to develop rapid, hand-held, inexpensive biosensors for detecting cardiac markers. In the present study, one of the cardiac markers (Troponin T) is detected using microfluidic based biosensor. Troponin T (cTnT) releases in to the blood serum within 4–6 h after minor heart attack and remains elevated for up to 2 weeks, which will help in diagnosing the heart condition. In this work, a microfluidic channel with an array of gold strips is considered for detecting and quantifying the Troponin T in an aqueous solution. Troponin T primary (capture) antibody is immobilized on gold strip using self assembled monolayer (SAM) consisting of a homogeneous mixture of oligo (ethylene glycol) (OEG)-terminated alkanethiolate and mercaptohexadecanoic acid (MHDA). Then, an aqueous solution containing Troponin T antigen is injected into the microchannel to facilitate antibody-antigen reaction to take place in less time. Later, FITC tagged Troponin T secondary (detection) antibody is dispensed in to the channel for quantification of Troponin T antigen. Using confocal fluorescent reader, the variation of fluorescent intensity across the microchannel is measured and quantified the concentration of Troponin T antigen with calibrated samples. Contact angle measurement system, Fourier Transform Infrared Spectroscopy and Ellipsometer are used to characterize the surface properties at each stage of biomolecule immobilization.
Unsteady Phenomena Induced Pressure Pulsation and Radial Load in a Centrifugal Pump With Slope Volute
Authors: Zhang Ning , Yang Minguan , Gao Bo , Li Zhong
Published: December 2013

Vibration in centrifugal pump still remains a tough problem to solve. Many studied have been done to find the relationship between hydraulic design and vibration. Both experiments and numerical simulation methods have been proposed to make clear the influence of pump parameters related to vibration. It is evident that unsteady phenomena in centrifugal pump are the main factors causing vibration. Also motor-stator interaction of impeller and volute keeps predominant role considering hydraulic factors.

Till now almost all reported researches consider pump geometry parameters, but the shape of volute is rarely proposed. To reduce interaction between impeller and volute tongue, a special volute with slope diffuser section is put forward in this paper. The relative position of volute tongue changes compared to the conventional spiral volute. Thus the effect of flow field striking with volute tongue can be receded effectively, and vibration will be reduced.

As the developing of computer technology, it is possible for us to achieve the unsteady flow field inner pump by using numerical simulation methods. A commercial software Fluent was adopted to analyze pressure pulsation and radial load of model pump. Slant angle and clearance rate were optimized considering pressure magnitude. It is observed that pressure amplitude at blade passing frequency achieve the lowest level at slant angle 15°. Pressure magnitude decreases significantly with the increasing of clearance, but limited to radial size of volute, it is suggested to be in the range of 0.134∼0.250.

Several monitor points are selected along the volute to have overall understanding of pressure pulsation characteristics. Pressure pulsation at blade passing frequency keeps the predominant in motor-stator interaction. Amplitude of both pressure and radial load increase rapidly when pump operating at off designed conditions.
A Wavelets Method for Solving Heat Transfer and Viscous Fluid Flow Problems
Authors: Sowayan A. S. , Bénard A. , Diaz A. R.
Published: December 2013

Wavelet-based methods have demonstrated great potential for solving partial differential equations of various types. The capabilities of the wavelet Galerkin method are explored by solving various heat transfer and fluid flow problems. A fictitious domain approach is used to simplify the discretization of the domain and a penalty method allows an efficient implementation of the boundary conditions. The resulting system of equation is solved iteratively via the Conjugate Gradient and Preconditioned Conjugate Gradient Methods. The fluid flow problems in the present study are formulated in such a manner that the solution of the continuity and momentum equations is obtained by solving a series of Poisson equations. This is achieved by using steepest descent method. The examples solved show that the method is amenable to solving large problems rapidly with modest computational resources.
Laminar and Transitional Boundary Layer Entropy Generation Over a Flat Plate Under Favorable and Adverse Pressure Gradients
Authors: Owen Landon D. , Xing Tao , McEligot Donald M. , Crepeau John C. , Budwig Ralph S.
Published: December 2013

Minimizing entropy generation is important to improve the efficiency of any system. The objective of this study is to use computational fluid dynamics (CFD) to elucidate the effects of pressure gradients on entropy generation rates in laminar and transitional boundary layers. The commercial CFD software, ANSYS FLUENT, is employed. The favorable and adverse pressure gradients are generated using various curved slip top walls. Bypass transition is simulated using the mean inlet velocity and Reynolds stresses from the direct numerical simulation (DNS) conducted by Nolan and Zaki [1]. Various turbulence and transitional models are employed and the results are compared to the DNS data. The factor of safety method is used to evaluate numerical error and grid uncertainties. Three systematically refined meshes are used to evaluate grid convergence. Monotonic convergence is achieved for all simulations with small grid uncertainties. The boundary layer correlation function, F(λ), the shear stress correlation, S(λ), and the dissipation coefficient, Cd, are calculated for the laminar CFD results. The dissipation coefficient, Cd and the intermittency, γ, are also calculated for the bypass transition CFD results. The laminar CFD results show better agreement with the correlation developed by McEligot than with the Thwaites correlation for F(λ) and S(λ). Overall, the percentage differences between the CFD results and the correlations increase as the magnitude of the pressure gradient variable, β, increases. The solvers and turbulence models in the transitional simulations are similar to the study by Ghasemi et al [2]. However, this study uses a much finer grid and improved boundary conditions for the inlet. These changes show an improvement for most turbulence models by comparison with the DNS results, especially for the location of transition.
Development of Double Suction Volute Pump for High Efficiency
Authors: Kobayashi Katsutoshi , Hagiya Isao , Akiniwa Hideki , Yoda Hiroaki , Senba Daijirou
Published: December 2013

The double suction volute pump consists of three components: a double suction flow path in upstream, an impeller with five blades, and a double volute flow path in downstream. The double suction was designed to improve a flow on the inlet surface of impeller. A significantly high pre-swirl velocity and low pre-swirl velocity were observed in original double suction, however its high pre-swirl velocity was slowed down and its low pre-swirl velocity was speeded up in designed double suction. As a result, the designed double suction had a more uniform velocity distribution on the inlet surface of impeller.

The impeller had twenty design parameters and those parameters were optimized by genetic algorithm (GA) to improve the impeller efficiency. A high total pressure loss was observed on the outlet surface of impeller and near the shroud wall of impeller meridian surface. On the other hand, its total pressure loss was decreased in optimized impeller, and the impeller efficiency increased by +0.7[%].

The cross-sectional surfaces, which were defined on a main streamwise curve of double volute, were designed to decrease a total pressure loss occurring inside double volute. In designed double volute, a secondary vortex on the cross-sectional surface was suppressed and a high circumferential velocity was decreased near the tongue and front edge of partition wall. As a result, the total pressure loss was decreased inside designed double volute.

The hydraulic pump performance for designed pump, which consisted of the designed double suction, optimized impeller and designed double volute, was predicted by numerical simulation. Efficiencies in double suction, impeller and double volute were increased by 0.6[%], 0.4[%] and 1.1[%] respectively and the total improvement of pump efficiency was 1.9[%]. The designed pump was manufactured and its hydraulic performance was measured by experiment. The numerical results of pump efficiency agreed well with experimental ones. The efficiency of designed pump increased by 2.0[%] compared with that of original pump in experiment.
The Influence of Working Fluid Characteristic Parameters on Turbine Performance for the Small Scale ORC System
Authors: Zhang Lei , Zhuge Weilin , Zheng Xinqian , Zhang Yangjun
Published: December 2013

The small scale Organic Rankine Cycle (ORC) using a turbine as expanders is considered as one of the most efficient ways to convert the waste heat energies of automobile engine into electrical energy, in the power range from several kW up to dozens of kW. In general, two important factors must be taken into account when designing the ORC turbine: the real gas effects of the organic fluid and the high expansion ratio presented in the machinery due to thermodynamic and efficiency factors. The characteristic parameters of R245fa have great difference compared with air. When designing an ORC turbine, the initial problem is the influence of the working fluid characteristic parameters on the turbine performance. Similarity analysis method is used to analyze this problem. When using the similarity theory to design two similar operating conditions, gas constant R and dynamic viscosity μ are easy to be taken into account as they have a dimension; specific heat ratio κ is hard to be taken into consideration. In this paper, a high expansion ratio ORC turbine is generated for a small scale ORC system working with the organic fluid R245fa, and the influence of κ on the turbine performance parameters analyzed.

Firstly, the turbine geometry is designed in an iterative process using the commercial design tool Concepts-NREC Rital program, and the designed operating condition is determined. Secondly, the similarity criterion numbers are deduced with no consideration of the specific heat ratio κ, and the similar operating condition is calculated by the deduced similarity criterion numbers. The results achieved by the one-dimensional design software Rital shows that the deviation of similarity criterion numbers is small, which indicates that the two operating conditions are similar. Then, to verify the conclusion above, the flow field simulation using one channel model is conducted based on the R245fa operating condition and air operating condition using the computational fluid dynamics (CFD) code NUMECA-FineTurbo. However, deviations of the similarity criterion numbers from the CFD results are more than twice to those from the one-dimensional results. The larger deviation may indicate that the influence of the specific heat ratio κ cannot be ignored. After that, the distributions of the total pressure, total temperature, the relative Ma number and entropy in the nozzle and rotor channel are compared. These results show that except the total temperature the distributions of the other three parameters are very similar. The similar distribution may indicate that the specific heat ratio κ has little influence on the efficiency and expansion ratio, but κ has greater influence on the temperature and output power. All of these conclusions are made according to the simulation results, the accuracy should be verified through the test results.
Microfluidic Device for Synthesis of Chitosan Nanoparticles
Authors: Cetin Barbaros , Taze Serdar , Asik Mehmet D. , Tuncel S. Ali
Published: December 2013

Chitosan nanoparticles have a biodegradable, biocompatible, non-toxic structure, and commonly used for drug delivery systems. In this paper, simulation of a microfluidic device for the synthesis of chitosan nanoparticle is presented. The flow filed together with the concentration field within the microchannel network is simulated using COMSOL Multiphysics® simulation environment. Different microchannel geometries are analyzed, and the mixing performance of these configurations are compared. As a result, a 3D design for a microfluidics platform which includes four channel each of which performs the synthesis in parallel is proposed. Future research directions regarding the fabrication of the microfluidic device and experimentation phase are addressed and discussed.
Development of PIV System for Jet Mixed Tanks
Authors: Muhammad Ibraheem R. , Bryant Harry C. , Allen Monica , Kizito John P.
Published: December 2013

Particle image velocimetry (PIV) is a very useful tool to measure fluid velocity in various systems. In the present study, an “in-house” PIV system was developed for fluid flow measurements in a jet mixed tank. The flow profile was observed for a single jet mixer in a rectangular shaped mixing tank with varying liquid height. The jet angle was varied for the studies from 0 to 45° from the center axis. The liquid height was varied from 17–26 cm. To ensure the system was able to provide accurate results, a gravity driven pipe flow problem was first set up. The PIV system was able to accurately capture the parabolic flow profile that is known to result from Poiseuille flow problems. Results from the jet mixing study showed that recirculation in the mixing tank as a result of the jet impingement on the tank walls varied due to the angle of the jet. Low mixing areas, or locations in which the velocity was minimum, was determined from the jets of different angles. Results showed that the velocity along the surface maintained the same profile for each of the three liquid levels studied. The velocity magnitudes decreased as the liquid level was increased.
Multi-Color Imaging Pyrometry Techniques for Gas Turbine Engine Applications
Authors: Estevadeordal Jordi , Tralshawala Nilesh , Badami Vivek
Published: December 2013

As part of a Department of Energy/GE sensors program multicolor pyrometry (MCP) imaging techniques were evaluated for incorporation into single color IR camera systems for gas turbine engine applications. MCP offers advantages over single-color band imaging pyrometry such as having less restrictive assumptions on wavelength dependent emissivity and capability to correct for optical density changes, contamination and fouling.

Several prototype imaging designs were built, tested and calibrated in jugular laboratory experiments and a design was implemented and demonstrated in gas turbine full-speed, full-load engine tests. Results of multicolor-color imaging and MCP temperature and apparent emissivity calculations are presented for a variety of laboratory experiment conditions, as well as for various blade conditions in the hot gas path region of turbine blades of a gas turbine engine. MCP and image processing algorithms are designed and applied to characterize the temperature and emissivity changes in the viewed surfaces in these experiments.
Numerical Study of the Influence of Viscosity on the Performance of an Electrical Submersible Pump
Authors: Sirino Thiago , Stel Henrique , Morales Rigoberto E. M.
Published: December 2013

This work presents a numerical analysis on the influence of viscosity on the performance of a semi-axial electrical submersible pump (ESP) such as the ones used in offshore petroleum production. A single stage composed of an impeller with seven blades and a diffuser with seven vanes is considered. Flow simulations for water and other fluids with viscosities ranging from 60 to 1020 cP were performed with the aid of Computational Fluid Dynamics, and both design and off-design flow rates and impeller speeds were investigated. The numerical model was validated with experimental measurements of the static pressure difference on a given stage of a three-stage ESP system. Results showed good agreement between the computed and the measured pressure difference values. Analyzes of the water flow inside the pump revealed that the flow is blade-oriented at the best efficiency point as expected, while large separation zones are found in the impeller and diffuser channels for part-load conditions. However, flow is not strictly blade-oriented at the best efficiency point for fluids other than the water. Examination of performance for water and fluids with higher viscosities shows that similarity laws are restricted for water, and that the best efficiency point is shifted when considering viscous fluids. Also, head values for viscous fluids are degraded not just due to viscosity and high flow rates, but also with rotor speed. The flow pattern analysis and the results found may provide useful information for engineers concerned with highly viscous fluid pumping and, possibly, shed some light on the understanding of more complex phenomena associated with actual offshore oil production operations such as multiphase pumping of viscous fluids.
Vortex Penalization Method for Solid-Porous-Fluid Media With Application to Passive Flow Control
Authors: Mimeau Chloé , Mortazavi Iraj , Cottet Georges-Henri
Published: December 2013

In this work, a coupling of vortex methods with penalization methods is proposed in order to accurately and easily handle solid-fluid-porous media. This immersed boundary approach indeed maintains the efficiency and the robustness of vortex methods and allows to model the three different media without prescribing any boundary condition. In this paper, we propose an application of this immersed boundary method to passive flow control around a semi-circular cylinder, realized adding a porous sheath on the obstacle surface in order to smooth the flow dynamics.
Development of High-Order Scheme in Unstructured Mesh for Direct Numerical Simulations
Authors: Yang H. Q. , Chen Z. J. , Dudley Jonathan G.
Published: December 2013

There has been a growing interest in higher-order spatial discretization methods due to their potential for delivering high accuracy at reasonable computational overhead for the Direct Numerical Simulation (DNS) of vortex-dominated flows. Many of the existing high-order schemes for unstructured grids use more degrees-of-freedom (DOF) in each cell to achieve high-order accuracy. This paper formulates and demonstrates a high-order correction method for unstructured grids. Using this approach, there is no increase in DOF within each cell. By adding higher order correction terms, higher order accuracy can be achieved. The present technique is innovative in that it can be readily added to existing lower order solvers, it can achieve very high-order accuracy, it is stable, and it can make use of either central or upwind schemes. Many examples are presented and used to demonstrate the high-order accuracy.
Effect of Rotor-Stator Configuration in the Generation of Vortical Scales and Wake Mixing in Single Stage Axial Fans: Part I — LES Modelling and Experimental Validation
Authors: Galdo Vega Mónica , Fernandez Oro Jesus Manuel , Argüelles Díaz Katia María , Santolaria Morros Carlos
Published: December 2013

The unsteadiness and vortical structures associated to impinging wakes convected through rotor and stator passages have been studied in detail in a single-stage low-speed axial fan, with 9 blades and 13 inlet/outlet guide vanes. In particular, in this first part, the effect of complementary rotor-stator (RS) and stator-rotor (SR) configurations has been addressed in terms of wake mixing and generation of vortical structures in both absolute and relative frames of reference.

A LES simulation of the midspan section (in a 2.5D model) is introduced to resolved the largest scales of the vortical motion within the wakes, related to vortex shedding, especially at off-design conditions. Chopping mechanisms and periodic interactions of the coherent turbulent structures are described and the presence of turbulent spots due to wake-wake interactions is revealed. Another relevant flow pattern, like the advection of leading edge separation through the downstream passage, is also identified and linked to the periodic potential interaction of upstream vanes (SR) or blades (RS).

Additionally, complete experimental databases of the time-resolved and the turbulent scales of the flow are available for both configurations by means of hot-wire anemometry measurements. Wake transport and viscous mixing are identified in corresponding measuring windows, and primary flow structures at midspan are also recovered and compared with the numerical results for validation.

From the comparison of experimental and numerical results it can be concluded that the numerical modeling is able to reproduce accurately the unsteady phenomena that occur inside the axial fan, and shows the potentiality of LES techniques to resolve with high fidelity the main turbulent structures present in the flow, especially at off-design flow rates.
Numerical Investigation of Pressure Fluctuation and Rotor-Stator Interaction in a Multistage Centrifugal Pump
Authors: Zhou Ling , Shi Weidong , Bai Ling , Lu Weigang , Li Wei
Published: December 2013

The unsteady flow field in a multistage centrifugal pump was simulated with ANSYS-CFX code based on transient rotor-stator method, and Shear Stress Transport (SST) turbulence model to investigate the pressure fluctuations in the three stages passages. With the Fast Fourier Transform (FFT) analysis, the pressure fluctuations and frequency domains are analyzed and compared between stages. The numerical results show that the pressure fluctuates at the blade passage frequency, and the maximum amplitude of blade passage frequency occurs in the region from the rotor to the stator when the impeller blade gets close to the diffuser vane leading edge. The pressure pulsation period mainly associated with the number of impeller blades, but the influence gradually reduce when the fluids flow into the diffuser. The flow patterns and pressure fluctuation between stags are similar.
Performance Evaluation of a Centrifugal Blower Using Optimal Design Method
Authors: Jang Choon-Man , Lee Jong-Sung , Yang Sang-Ho
Published: December 2013

Effects of design variables on the performance of a centrifugal blower have been analyzed based on the three-dimensional flow analysis. Two design parameters defined the shape of a volute casing are introduced to enhance a blower performance. To analyze three-dimensional flow field in the centrifugal blower, general analysis code, CFX, is employed in the present work. SST turbulence model is employed to estimate the eddy viscosity. Boundary condition at the interference plane between rotational and stationary domains is applied by a stage method. Unstructured grids are used to represent a composite grid system including blade, casing and inlet guide.

In the present study, throughout the shape optimization of the centrifugal blower at the design flow condition, the blower efficiency and pressure are successfully increased by 0.5 and 1.6 percent compared to reference one. It is found that the casing height of design variables is more sensitive on the object function of efficiency compared to that of the casing width. And secondary flow due to velocity gradient and low velocity region increase pressure loss, leading to make low efficiency. Detailed flow field inside a centrifugal blower is also analyzed and compared.
A Steady State, Adiabatic Compression and One-Dimensional Generalized Flow Analysis of a Natural Gas Pipeline Using Soave-Redlich-Kwong Equation of State
Authors: Oumechouk Hicham T. , Ait-Ali Mohand A.
Published: December 2013

Steady state adiabatic compression and one-dimensional generalized gas flow is analyzed using governing conservation laws and Redlich-Kwong-Soave (R-K-S) equation of state applied to a representative mixture of natural gas. The objective of this work is to obtain the state properties of the natural gas considered as an open thermodynamic system at compressor and gas pipeline exits, then the compressor power and energy auto-consumptions for a few diameters and pipe line lengths configurations. The adiabatic, irreversible compression process is analyzed with formal state property definitions where departures from ideal gas properties are obtained using R-K-S equation of state. The one-dimensional generalized gas flow problem is analyzed with continuity, momentum and energy equations, combined with the equation of state; Reynolds analogy between heat transfer and flow friction is adopted. This problem is thus defined with four non linear coupled differential equations; the variables to be determined are pressure, temperature, specific volume and velocity at the gas pipeline exit. The adopted calculation procedure to obtain the gas properties is iterative. It assumes pressure and temperature initial values, solves the equation of state for the specific volume and the continuity equation for the velocity, then corrects for pressure and temperature with integrated values to be used with the next iteration from a solution of the differential equations of motion and energy. This procedure is applied to a few gas pipeline configurations of pipe diameters sections and number of boosting compressor stations for a gas pipeline capacity of 13.5 billions standard cubic meters per year to be delivered to a natural gas liquefaction plant located at a sea port at a distance of some 350 miles.
Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
Authors: Galván Sergio , Reggio Marcelo , Guibault Francois
Published: December 2013

In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the diffuser efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.
An Experimental Study on Flow Past an Equilateral Triangular Prism at Intermediate Reynolds Number and the Effect of its Orientation
Authors: Agrawal Namit , Dutta Sushanta , Gandhi B. K.
Published: December 2013

This paper explores the effect of two orientations (0° and 180°) on near wake region of an equilateral triangular prism at intermediate Reynolds number. The paper also investigates the effect of Reynolds number on the near wake region at intermediate regime. Two orientations are defined such that the apex of the equilateral triangle is pointing upstream and downstream respectively. The flow field behind a triangular prism is different in these two orientations. When apex angle points upstream it corresponds to a fore-body attached to a flat plate while when apex angle points downstream the flat face acts like a flat plate with an after body attached to it. This after-body penetrates the recirculation zone formed behind the flat plate. These two effects are investigated for various Reynolds numbers in intermediate regime. Factors affecting drag coefficient and Strouhal number are different in both cases. In first case the fore-body changes the flow before it gets separated in two free shear layers. In other words, the fore-body affects the free shear layers formed and hence the drag. In the second case, the two shear layers are formed first then their interaction is modified by the after-body in the near wake region behind the prism. Particle Image Velocimetry (PIV) and Hotwire anemometry is being used in present study. Detailed flow field is investigated in terms of velocity magnitude, stream traces, vorticity contours, centerline recovery, power spectra, velocity profiles, Strouhal number and drag coefficient.
Fully Resolved Simulation of Particulate Flow Using a Sharp Interface Direct Forcing Immersed Boundary Method
Authors: Yang Jianming , Stern Frederick
Published: December 2013

In this paper, the sharp interface, direct forcing immersed boundary method developed by Yang and Stern (A simple and efficient direct forcing immersed boundary framework for fluid-structure interactions, J. Comput. Phys. 231 (2012) 5029–5061) is applied to the fully resolved simulation of particulate flow. This method uses a discrete forcing approach and maintains a sharp profile of the fluid/solid interface. Also, it employs a strong coupling scheme for fluid-structure interaction through a predictor-corrector algorithm. The fluid flow solver is not included in the predictor-corrector iterative loop thanks to the direct forcing idea, which makes the overall algorithm highly efficient and very attractive for the fully resolved simulation of particulate flow with numerous solid particles. Several cases including sedimenting and buoyant particles and the interaction of two sedimenting particles showing kissing, drafting, and tumbling phenomenon are examined and compared with the reference results to demonstrate the simplicity and applicability of our method in particulate flow simulations.
Computing Profiles of Porosity and Surface/Volume Ratio in a Packed Bed Using Monte Carlo Method
Authors: Li Genong
Published: December 2013

Porosity and surface/volume ratio are two important parameters for a packed bed. In cylindrical packed beds at low tube-to-particle diameter ratio, they vary greatly in the radial direction. In the existing literature, radial profiles of porosity and surface/volume ratio have been computed using some analytical equations which involve elliptic integrals. In this paper, a Monte Carlo method is used to compute those profiles. To the authors’ knowledge, the method has never been employed in this context. The procedure of using this novel method is explained in detail. Through a rigorous error analysis based on statistics, the accuracy of the simulation result can be controlled. Before any simulation, the number of sampling points needed in the Monte Carlo simulation can be determined given an accuracy requirement. The method is completely general and can be used to compute profiles of porosity and surface/volume ratio in any packed bed with any shape of packing elements.
Mysterious Behavior of Optimization Calculation With MOGA
Authors: Lee Yu-Tai
Published: December 2013

Multi-Objective Generic Algorithm (MOGA) is a popular and viable optimization calculation scheme for many practical engineering problems. This is because MOGA provides reliable search results covering wide and multi-variable design spaces. Most importantly when an optimization problem involves using mixed design variables, i.e. continuous and discrete variables, MOGA is still applicable. However, in such a condition MOGA needs to be programmed in a binary mode, which requires a minimum number of bits to represent each real and integer design variable. The accuracy of the prediction of the optimization calculation is expected to depend on the number of bits used. This paper introduces such a problem based on a general turbomachinery design problem. The design variables of the centrifugal impeller design consist of discrete and continuous variables. Some puzzling behavior occurred when the optimization calculation was carried out, related to the prediction accuracy when applying different number of bits to represent the continuous and discrete design variables. It is found that the accuracy is independent of the number of binary bits used. Detailed analyses were performed using simplified analytic formulations for the objective functions to determine why the calculated results show such a behavior. In addition, objective functions are developed and verified that do not show this behavior.