bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Effects of Incidence Angle on the Mean Wake of a Surface-Mounted Finite-Height Square Prism
Authors: Ogunremi Ayodele , Sumner David
Published: November 2015

The wake of a surface-mounted finite-height square prism of sub-critical aspect ratio AR = 3 was studied experimentally in a low-speed wind tunnel at a Reynolds number of Re = 3.7×104. The ratio of the boundary layer thickness on the ground plane, to the width of the prism, was δ/D = 1.5. The incidence angle of the prism was varied from α = 0° to 45°. Wake mean velocity measurements were made in vertical planes normal to and parallel to the main flow direction using a seven-hole pressure probe. As the prism is rotated from α = 0° to 45°, the mean wake progressively widens and the maximum streamwise extent of the mean recirculation zone increases. The mean streamwise tip vortex pair is symmetric at 0° and 45°, but becomes strongly asymmetric at intermediate α, where the tip vortex is found higher above the ground plane on the wider side of the wake. The wake and tip vortex asymmetry is most pronounced near the critical incidence angle.
Numerical Optimization of a Piece-Wise Conical Contraction Zone of a High-Pressure Wind Tunnel
Authors: Hasselmann Karsten , Reinker Felix , aus der Wiesche Stefan , Kenig Eugeny Y.
Published: November 2015

The Organic Rankine Cycle (ORC) offers a great potential for recovering waste heat and using low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and, therefore, designing ORC components with high efficiencies and minimized losses is of major importance. Such an approach requires the use of a specially designed closed cascade wind tunnel. This contribution presents the design of the contraction zone shape. The ideal shape can be defined by a sixth order polynomial yielding a smooth curve for the nozzle profile. Due to pressure vessel costs, it is not possible to realize the whole contraction zone as one piece for this wind tunnel. Instead, a piece-wise conical design approach is chosen. Classical nozzle design guidelines do not offer an analytical solution to this flow problem. Therefore, computational fluid dynamics (CFD) in combination with Stratford’s separation criterion is used for an optimization study of a piece-wise conical contraction zone. Different combination of numbers of components, length, and inflection points are investigated. The optimization minimizes the flow deviation of the chosen profile to the optimal shape in two steps: a geometrical approach to the optimal shape and an optimization of the flow field within the contraction zone. The geometrical optimization yields a profile with minor deviation to the ideal shape. For the flow field optimization, a CFD analysis is used to minimize flow separations at the break points between the single conical pieces, especially those at the far end of the contraction zone. All shapes are investigated by Stratford’s separation criterion, which is adopted to conical pieces. The presented analysis indicates that the flow field optimization yields a much better approach for the fluid dynamics of the wind tunnel than the geometrical approach.
Aerodynamic Investigation of a Passive Secondary Jet Exciting a Separation Bubble for a Blunt Flat Plate
Authors: Helcig Christian , aus der Wiesche Stefan , Uhkoetter Stephan
Published: November 2015

The aim of this study is to examine the influence of passive jets interacting with the separation region of the flow around a blunt plate. Experimental and numerical analysis are used to measure the velocity within the separation and reattachment region of the blunt plate with different passive jet configurations. A blunt plate was placed in a low speed wind tunnel to conduct Laser-Doppler anemometry (LDA) measurements at Re = 2.06 × 104. For the numerical procedure a dynamical sub-grid model for Large Eddy Simulations (LES) was used. For all configurations the flow characteristics such as the reattachment length were determined to characterize the boundary layer. The passive jets showed a strong influence by interacting with the boundary layer of the blunt plate.
The Confined Flow Behavior of a Bingham Non-Newtonian Jet
Authors: Hammad Khaled J.
Published: November 2015

The flow behavior of a confined viscoplastic non-Newtonian jet is investigated numerically within the steady laminar flow regime. The Bingham constitutive equation is used to model the rheology of interest. A parametric study is implemented to investigate the influence of confinement ratio and rheology over the following range of parameters: Confinement ratio, CR = {5, 10, 20}, and Yield number, Y = {0, 0.5, 2}. A large corner recirculation region typically characterizes the flow of a confined Newtonian jet. However, in the case of a Bingham viscoplastic jet, once a critical yield number is exceeded, flow recirculation is eliminated and a stagnant corner region is formed. The confinement ratio has a dramatic impact on the recirculation intensity and the evolution characteristics of the jet only in the case of Newtonian flows, i.e. Y = 0. In general, a more intense recirculation is associated with higher confinement ratios. The extent and the strength of flow recirculation are found to significantly diminish with the yield number. The axial penetration of the confined jet substantially increases with the confinement ratio for Newtonian fluids only and decreases with the yield numbers for all confinement ratios.
Numerical and Experimental Study on Negative Buoyance Induced Vortices in N-Butane Jet Flames
Authors: Xiong Yuan , Suk Cha Min , Ho Chung Suk
Published: November 2015

Near nozzle flow field in flickering n-butane diffusion jet flames was investigated with a special focus on transient flow patterns of negative buoyance induced vortices. The flow structures were obtained through Mie scattering imaging with seed particles in a fuel stream using continuous-wave (CW) Argon-ion laser. Velocity fields were also quantified with particle mage velocimetry (PIV) system having kHz repetition rate. The results showed that the dynamic motion of negative buoyance induced vortices near the nozzle exit was coupled strongly with a flame flickering instability. Typically during the flame flickering, the negative buoyant vortices oscillated at the flickering frequency. The vortices were distorted by the flickering motion and exhibited complicated transient vortical patterns, such as tilting and stretching. Numerical simulations were also implemented based on an open source C++ package, LaminarSMOKE, for further validations.
Hydrodynamic Performance and Shape Considerations of a Compact AUV for Riverine Environments
Authors: Papadopoulos George
Published: November 2015

The riverine environment presents an interesting operational challenge for an autonomous underwater vehicle (AUV). The fluid dynamics involved are complex and in many ways more demanding than the open ocean waters for which most current vehicles have been designed for. These dynamics encompass strong head-on and side currents, shallow waters with bottoms that may be either rocky, hard or soft mud, topological bends or bifurcations that can lead to strong secondary flows, and local dense vegetation or artificial structures that introduce local flow perturbations. As an initial first step to engineering an AUV shape that can perform well in the riverine environment, one needs to better understand the fluid dynamics involved, both from a discrete, as well as, from a compounded point of view. The current paper reports on an ongoing investigation into the flow physics and dynamics involved within the riverine environment, with the interest of generating requirements that can provide guidance into AUV shape design. A cylindrical shape of high length-to-diameter ratio, indicative of most previously developed AUVs, serves as the nominal point of departure for the analysis.
Wind Tunnel Investigation of a Double Stacked Wagon in Free-Stream
Authors: Li Chao , Kost Michael , Burton David , Sheridan John , Thompson Mark C.
Published: November 2015

The surface flow structure and pressure distribution of a model representative of a 48ft, double-stacked container wagon of an intermodal freight train is characterized. The model used is 1: 14.6 in scale, and all experiments are conducted in Monash University’s 450kW closed loop wind tunnel. The model employs 474 pressure taps in total, and data is logged with two dynamic pressure-measuring systems. Flow visualizations are carried out on the top and side surfaces using fluorescent Kaolin china clay with kerosene as a carrier. Testing is performed under three different floor boundary-layer profiles in order to assess the sensitivity of the surface flow variation in the floor boundary-layer. It is shown that in a time-averaged sense, the shear-layer separating off the leading edges of the wagon roll up to form three recirculating bubbles on the top and side surfaces. The consequent surface pressure profile matches closely to that of a surface-mounted cube where top and side pressure recovery occurs. For the three boundary-layer profile tested, pressure distribution displays very minor changes. A Karman like left-right wake shedding is observed in the wake with a shedding frequency of St = 0.195.
Comparison of Three Slip Velocity Models for a Centrifugal Impeller
Authors: Lee Yu-Tai
Published: November 2015

The slip velocity model has been created to account for the effects produced by the difference in velocities between the suction side and the pressure side of the blade at the centrifugal impeller exit. The model is applied to reduce the ideal tangential velocity and provides an estimation of the impeller exit velocity and blade loading for use in turbomachinery meanline modeling. Wiesner reviewed all the proposed models in 1967 and came up with a set of formulations which are only dependent on the impeller geometry, such as number of blades, exit blade angle and blade inlet-to-exit radius ratio. In order to cover flow induced effects and off-design conditions, Qiu recently proposed a formula which contains the effects from the radial rotation, blade turning and passage width variation. For a centrifugal impeller, often the impeller exit condition is affected by downstream components. Pfleiderer’s model of 1961 includes effects of downstream vaned diffuser, vaneless diffuser, or a volute. This paper focuses on the comparisons of the three models in predicting blade loading for a centrifugal-fan impeller with a double-discharge volute at both design and off-design conditions. The comparisons reveal not only each model’s prediction accuracy, but also the flexibility of each model.
Extracting Static Pressure From Velocimetry in Vortical Flows
Authors: Merkl Jackson , Hiremath Nandeesh , Raghav Vrishank , Komerath Narayanan
Published: November 2015

The problem of extracting static pressure fields on and away from flow boundaries in complex flows, is considered. Given the correct velocity field in steady incompressible flow, an assumption of constant or known stagnation pressure allows finding the static pressure. This gives an upper bound on static pressure, and is in fact close to the real answer. The technique developed here is to start with the measured, ensemble-averaged 3-component velocity field in a periodic flow. The static pressure field computed from this velocity field in incompressible flow can be used along with the velocity field as the starting guess of a solution in a Navier-Stokes solver. The method is applied to the bottom surface near the sharp edge of a rotating rotor blade in the reverse flow domain encountered at high advance ratio in a wind tunnel. The drop in stagnation pressure along given streamlines even through the sharp-edge vortex, is shown to be very small, so that the effect on the static pressure estimate is minor. The pressure field successfully explains some features that could not otherwise be explained.
The Experimental Study of Water Accumulation in PEMFC Cathode Channel
Authors: Bozorgnezhad Ali , Shams Mehrzad , Ahmadi Goodarz , Kanani Homayoon , Hasheminasab Mohammadreza
Published: November 2015

In the recent years, Proton Exchange Membrane Fuel Cell (PEMFC) has attracted much attention as a source of green energy and alternative to internal combustion engines. The PEMFC produces electrical power with heat and water as only byproducts. Water is needed to providing proper hydration of membrane and its ionic conductivity in PEMFCs, but excess water accumulation known as flooding phenomenon decreases reaction sites on gas diffusion and increases mass transport loss and consequently it leads to performance loss of PEMFC. Proper water management depends on characterization and study two-phase flow phenomenon of PEMFC as flooding. In the present work, the two-phase flow in the cathode channel of transparent PEMFC with single serpentine flow field is studied by direct optical visualization and utilization of Digital Image Processing for different inlet flow parameters and operational conditions. Liquid water accumulation in the cathode channel is quantified and the water coverage ratio is calculated as a scale of water content of the cathode channel in the unsteady and time-averaged states. Increasing the temperature and stoichiometry decrease the accumulation of liquid water in the cathode channel while increasing the reactants relative humidity leads to accumulation of more liquid water. Observations show in higher cathode stoichiometries, the effect of anode stoichiometry on the water coverage ratio decreases. The effect of anode stoichiometry on the water coverage ratio is more than the cathode stoichiometry.

In higher anode stoichiometries, the effect of cathode stoichiometry on the water coverage ratio decreases so that the change in cathode stoichiometry has no significant effect on the values of water coverage ratio.
Near Wall Turbulence Effects on Particle Transport and Deposition in Human Tracheobronchial Multi-Level Bifurcation Model
Authors: Mofakham Amir A. , Tian Lin , Ahmadi Goodarz
Published: November 2015

Transport and deposition of micro and nano-particles in the upper tracheobronchial tree were analyzed using a multi-level asymmetric lung bifurcation model. The multi-level lung model is flexible and computationally efficient by fusing sequence of individual bifurcations with proper boundary conditions. Trachea and the first two generations of the tracheobronchial airway were included in the analysis. In these regions, the airflow is in turbulent regime due to the disturbances induced by the laryngeal jet. Anisotropic Reynolds stress transport turbulence model (RSTM) was used for mean the flow simulation, together with the enhanced two-layer model boundary conditions. Particular attention is given to evaluate the importance of the “quadratic variation of the turbulent fluctuations perpendicular to the wall” on particle deposition in the upper tracheobroncial airways.
Numerical Study of Flow Dynamics in Human Eye Vitreous Chamber After Vitrectomy and Gas Tamponade
Authors: Yousefi Ali , Abouali Omid , Ghoshtasbi Rad Ebrahim , Ahmadi Goodarz
Published: November 2015

The purpose of this study is to evaluate the flow pattern and the fluid shear stress acting on the retinal wall in a human eye vitreous chamber after Vitrectomy and gas tamponade including the effect of saccadic eye movements. The correlation between the maximum shear stress induced on the retinal wall and the gas fill fraction (GF) and saccade amplitudes was investigated. In modeling the geometry of vitreous chamber cavity, the indentation of the lens was taken into account. The two-phase flow at the recovery phase of the operation was modeled numerically. Unsteady three-dimensional forms of continuity and Navier-Stokes equations were solved. Volume-of-fluid method was used to solve the two-phase flow in the eye. Saccadic motion of the eye was modeled using the dynamic mesh technique. The numerical model was validated by comparing the results with the available analytical solutions and experimental data for a spherical model. Then, numerical simulation was performed based on the deformed sphere configuration, representing a more realistic model of vitreous chamber cavity. The simulation results were compared with the available numerical studies for the spherical geometry. Then the wall shear stress on the retina was computed and compared for various gas fractions. The potential effect of wall shear stress on the retinal detachment and the need for post-operation posturing in all studied cases were discussed.
Optimization of Looped Airfoil Wind Turbine (LAWT™) Design Parameters for Maximum Power Generation
Authors: Banerjee Subhodeep , Song Binhe , Syrovy George , Agarwal Ramesh K.
Published: November 2015

The looped airfoil wind turbine (LAWT™) is a patented new technology by EverLift Wind Tecnology, Inc. for generating power from wind. It takes advantage of the superior lift force of a linearly traveling wing compared to the rotating blades in conventional wind turbine configurations. Compared to horizontal and vertical axis wind turbines, the LAWT™ can be manufactured with minimal cost because it does not require complex gear systems and its blades have a constant profile along their length [1]. These considerations make the LAWT™ economically attractive for small-scale and decentralized power generation in rural areas. Each LAWT™ is estimated to generate power in the range of 10 kW to 1 MW. Due to various advantages, it is meaningful to determine the maximum power generation of a LAWT™ by optimizing the structural layout.

In this study, CFD simulations were conducted using ANSYS Fluent to determine the total lift and drag coefficient for a cascade of airfoils. The k-kl-ω turbulence model was used to account for flow in the laminar-turbulent transition region. Given the lift and drag coefficients and the kinematics of the system, an analytical formula for the power generation of the LAWT™ was developed. General formulas were obtained for the average lift and drag coefficients so that the total power could be predicted for any number of airfoils in LAWT™. The spacing between airfoils was identified as the key design parameter that affected the power generation of the LAWT™. The results show that a marked increase in total power can be achieved if the optimum spacing between the airfoils is used.
Numerical Investigation on Saturated Boiling Heat Transfer in a Vertical Rectangular Minichannel
Authors: Cai Weihua , Ma Hongqiang , Yao Yang , Jiang Yiqiang
Published: November 2015

A numerical method based on the Euler-Euler model was developed to investigate the mechanism of saturated boiling heat transfer mechanism on upward flow in a vertical rectangular minichannel. This method validated by the experimental data from literature. At the same time, the mechanism of saturated boiling heat transfer was also investigated by ANSYS CFX for Freon R21 at high vapor quality in a vertical rectangular minichannel based on the above numerical method. The results show that the simulation results are good agreement with experimental data from reference and the deviation is within ±15%. The main boiling mechanism is forced convective boiling while the contribution of nucleate boiling is slight for saturated boiling heat transfer at high vapor quality. The evaporation of dispersed liquid phase should be also a main boiling heat transfer mechanism. These results will provide some constructive instructions for the understanding of saturated boiling heat transfer phenomenon in a vertical rectangular minichannel of PFHE.
Numerical and Experimental Investigation of Heat Transfer Coefficient and Friction Factor in Internal Channels With Fins
Authors: Regmi Pramesh , Chandra Pankaj R. , Zhang Ning
Published: November 2015

Surface heat transfer enhancement is widely used in a wide range of industrial applications. The turbulence created by the enhancement has significant effects on increasing the heat transfer. On the other hand, the surface enhancement usually causes a larger friction that leads to a larger pressure drop. In this study, an experimental investigation with computational verification of the wall heat transfer and the friction characteristics of a fully-developed turbulent air flow in a square channel with circular micro-fins was reported. The protuberances of 6.35×10−3 m diameter and 6.35×10−3 m height were placed in three different configurations. Tests were performed for the Reynolds numbers ranging from 27,000 to 96,000. The fin height-to-channel hydraulic diameter ratio, e/Dh, was kept at 0.125. The channel length-to-hydraulic diameter ratio, L/Dh, was 20. The heat transfer was enhanced using micro-fins as turbulence promoters. The computational analysis was also performed and found in close agreement with the experimental results. The simulations can be used in predicting local turbulence characteristics, thus the turbulence-heat transfer relationship. The simulation results can also predict the local heat and friction characteristics and in locating high temperature regions, or “hot spots,” which is beyond the potential of the experimental setup. This investigation could be helpful in applications concerning internal channel turbulent flows and involving micro-fins to boost heat transfer. Heat Exchangers, Air Compressors, Turbines are some of equipment where the results of this study can be utilized.
CFD Simulation of a Supersonic Steam Ejector for Refrigeration Application
Authors: Su Liju , Agarwal Ramesh K. , Banerjee Subhodeep
Published: November 2015

Supersonic steam ejectors are widely used in many industrial applications, for example for refrigeration and desalination. The experimental evaluation of the flow field inside the ejector is relatively difficult and costly due to the occurrence of shock after the velocity of the steam reaches over the sonic level in the ejector. In this paper, numerical simulations are conducted to investigate the detailed flow field inside a supersonic steam (water vapor being the working fluid) ejector. The commercial computational fluid dynamics (CFD) flow solver ANSYS-Fluent and the mesh generation software ANSYS-ICEM are used to predict the steam performance during the mixing inside the ejector by employing two turbulence models, the k-ω SST and the k-ε realizable models. The computed results are validated against the experimental data. The effects of operating conditions on the efficiency of the ejector such as the primary fluid pressure and condenser pressure are studied to obtain a better understanding of the mixing process and entrainment. Velocity contours, pressure plots and shock region analyses provide a good understanding for optimization of the ejector performance, in particular how to increase the entrainment ratio.
Effect of Brownian Dynamics on Ellipsoidal Fibers in Human Tracheobronchial Airways
Authors: Tian Lin , Ahmadi Goodarz
Published: November 2015

In vitro and vivo studies and observation of patients’ tissues have linked the occurrence of respiratory cancer to human exposure to asbestos fibers. While substantial evidences identified the ultra-fine fibers with diameter < 0.25 μm posing the highest carcinogenicity, the details of such correlation is still not fully understood. Particles in the submicron range are known to exhibit random Brownian motion and the intensity are well correlated to inversely to the particle dimension. The process of fiber Brownian motion and the extent that it affects the fiber transport and deposition in human tracheobronchial airways is very important but largely unknown. In this study, the motions of ultra-thin fibers were analyzed by solving the system of coupled equations for translational and rotation motion of fibers under the action of hydrodynamic drag and torque, shear induced lift, gravitational sedimentation, turbulence dispersion and Brownian diffusion in a human airway bifurcation model. Based on the performed simulations, the relationship of fibers’ hydrodynamic characteristics and Brownian dynamics on the fibers’ transport behavior were quantitatively explored. The carcinogenicity if fibers in the light of new findings was discussed.
Experimental Investigation of a Counter-Rotating Mixed-Flow Single Stage Pump Under Cavitation Conditions
Authors: Tosin Stefano , Friedrichs Jens , Dreiss Andreas , Schiavello Bruno , Elebiary Kariem
Published: November 2015

The increase in power per unit volume in modern pumps has been driven by manufacturing cost reduction. The first prototype of a new generation of centrifugal pumps has been experimentally and numerically investigated. It presents a particular and novel design characterized by the absence of any stator blade, which has been substituted with a counter-rotating radial impeller. According to an exhaustive literature survey, the usage of a mixed-flow impeller as a front rotor, followed by a radial-flow impeller seems to be a novel approach in pump design. The combination of a high specific speed impeller with a low specific speed counter-rotating diffuser produces flexible adaptability against varying working conditions. It also gives a rise to an increase of pressure coefficient values beyond limits of similar volute envelope. Applying the counter-rotating design principle to a radial pump increases power density, however cavitation-related issues remains a limiting factor. Counter-rotating design also features an additional degree of freedom to the system due to the independency of motor speeds of one another. This aspect improved cavitation inception characteristics especially at overload capacities. Moreover, such an arrangement required building a special test rig in order to accommodate for the double motor configuration. In this study, the NPSH3% -curve and the NPSHic cavitation inception characteristics have been measured. The system dependency on speed ratio variation has been also investigated along with the influence of the speed ration on the cavitation. Results of the cavitation inception visualizations were obtained using an endoscope at front rotor in order to analyze the behaviour of the pump under cavitation conditions. Test results showed two distinct speed ratios where maximum head and best cavitiaiton behavior were achieved. Additionally, results also confirmed that the cavitaion-free range can be optimized by using different speed ratios. A head drop-efficiency curve with variable speed ratios, which have been progressively adjusted for several flow capacities, is developed. This curve highlights the advantage of this new design compared to a conventional pump particularly under off-design conditions. It is clearly evident that delaying head deterioration, due to low inlet available suction energy, is solely attributed to the variable speed ratio of the runners.
CFD Analysis of the Pump Performance With Different Liquid Viscosity
Authors: Strongin Mikhail P.
Published: November 2015

The pumping of liquids with different viscosity is used in many industrial applications from automotive to food processing. Change of viscosity may have high influence on the pump performance. Therefore, it is important to compare efficiency of the same pump by pumping different liquids with large variety of viscosity through them.

In the present work the behavior of flows in the centrifugal pump with viscosity in the range from 10−3 to 1 kg/(m*s) is studied.

The pump model consists of suction, impeller, and discharge parts, which were studied as a single entity. This setup naturally permits analysis of the effects of non-uniformity of velocity. Full geometry was considered due to the absence of symmetry on the volute part of the pump.

K-ω SST turbulence closure model was used for these simulations. Commercial code Fluent 15.07 was chosen for Computational Fluid Dynamics (CFD) calculations. Multiple Reference Frame (MRF) model for steady state calculations was selected with the total of 3.4 million cells. Control transient calculations were done with sliding mesh approach. Transient and steady state cases showed a difference in the head within 5%.

The results show the drop of the pump head (∼ 4%) and efficiency (∼ 9%) with change the Re number on the inlet from 500,000 to 50,000 or kinematic viscosity from 10−6 to 10−5 m2/s respectively with the same flow rate. Model results show that at Re = 5,000 head dropped by 15% and efficiency by 35% in comparison to the case where Re = 500,000.

Moreover, the calculations showed that the blockage effect of large flow for high flow rate (>1.7 BEP) for Re < 5,000 appeared on the volute discharge side. Blockage effect was due to cavitation.

CFD simulations of the influence of liquid viscosity on the pump performance can help prepare practical recommendations for designers.
Design and Optimization of a Vertical Turbine Pump
Authors: Xia Yanjun , Maddox George , Lowry Sam , Ding Hui
Published: November 2015

An example of the complete process used by PumpWorks 610, LLC in designing and optimizing a vertical turbine pump is presented, starting with the creation of an initial prototype using the design software CFturbo®, and the subsequent virtual testing and analysis with the CFD tool PumpLinx®. The results of the CFD analysis are used to identify the sources of loss of efficiency, with specific examples of how those losses are identified. The geometry of the pump is then modified to improve performance and re-tested in the virtual environment before any hardware is manufactured. Once built, the predicted performance of the optimized pump is verified by physical testing. Comparisons between the CFD predictions and the empirical data are presented. Once demonstrated to perform as intended, the final design is delivered to the customer.
The Effects of Variable-Inlet Guide Vanes on Performance of an Axial Flow Pump With Tip Clearance
Authors: Feng Wei-Min , Pan Jing-Ye , Guo Zhi-Wei , Cheng Qian
Published: November 2015

The effects of variable-inlet guide vanes on the performance of an axial flow pump considering tip clearance are investigated. The performance and the main flow field of the whole passage with five different angles of inlet guide vanes ( −10°, −5°, 0°, 5°, 10°) and with two tip clearance sizes (1‰ and 2‰) are presented. The results show that when the angle of inlet guide vane increases from negative values to positive values, the pump head reduces for two tip clearance sizes. This is mainly caused by the change of inlet velocity triangle of blade. Moreover, as tip clearance size increases from 1‰ to 2‰, both the pump head and efficiency decrease because of increasing of the strength of tip clearance leakage vortex and reverse flow.
The Design of a Degassing Pump Based on Numerical and Experimental Research
Authors: Xie Dongjie , Wu Peng , Wu Dazhuan
Published: November 2015

In the food industry, it is necessary to remove the gas in liquid, in order to prevent the juice from oxidation and prolong guarantee period. At present, vacuum tanks are widely used in beverage productive process to remove air. However, the vacuum tanks are usually bulky and of high energy consumption.

In this study, the purposes of degassing pump design are: (1) effectively removing free gas and dissolved gas in liquid, (2) conveying the liquid, (3) more energy efficient than vacuum tank. In this process, numerical method is adopted to simulate the gas-liquid separation with eulerian multiphase model and population balance model (PBM) using the commercial code FLUENT.

Structures of pulp pump and gas-liquid cylindrical cyclone separator are used for reference. The degassing pump mainly consists of inlet tube, centrifuge drum, exhaust tube, impeller, volute and outlet tube etc.

The numerical simulation results show that there is a huge low pressure area in the center of the drum. Free gas and dissolved gas are separated into the low pressure region under the effect of centrifugal force and local low pressure.

Bubble diameter has a great impact on the degassing effect. PBM which considers bubbles coalescence and breakup is adopted here to calculate the diameter of bubbles. The drum diameter has an extremely influence on the inlet pressure of degassing pump. The centrifuge drum is installed in front of impeller, so pre-swirl of the fluid inside impeller inlet is strong. The hydraulic performance of pump slightly declines when centrifuge drum is added in numerical calculation.

The degassing pump is in manufacturing and will be tested in future.
An Examination of Changes in Bat Flight Kinematics During Take Off
Authors: Matta Alexander , Bayandor Javid , Müller Rolf
Published: November 2015

The powered flight of bats is unique in nature because of the agility that it allows them to achieve in comparison to other flying animals of equivalent size. One example of this is a bat’s ability to take off with no initial freestream velocity and transition to cruising flight over the duration of relatively few wing beat cycles. Bat’s wings are highly complex and have 20+ degrees of freedom (DOFS) per wing. Adjustments to several of these DOFS occur to allow for quick transition to cruising flight. In order to capture this transition in wing motion, video of Great Himalayan Leaf-Nosed Bats (Hipposideros Armiger) was captured over a period that included both take off and cruising flight. Images captured using a multi-camera setup, containing three rings of 10 RGB cameras each, were used in conjunction with triangulation techniques to capture the 3D coordinates of marker points on the wing. This setup eliminated the point dropout that can occur due to occlusion in traditional 2 camera systems due to its 360 degree coverage. Furthermore, the redundancy caused by collecting 3 or more 2D marker point projections from some of the 10 cameras per ring improved accuracy of the 3D coordinates. In order to capture the transition in wing kinematics, changes in flap amplitude, velocity, and frequency, were recorded. The data suggests that this species of bat utilize a change in flap amplitude as the primary means to transition from takeoff to cruising flight while keeping other parameters such as angle of attack and flap frequency constant.
The Effects of Fuel and Air Mixtures in Non-Premixed Combustion for a Bluff-Body Flame
Authors: Chen Lu , Battaglia Francine
Published: November 2015

The bluff-body stabilized flame is used in a numerical study of the non-premixed flames. This paper shows numerical investigations on the effects of hydrogen compositions and nonflammable diluent mixtures on the combustion and NO emission characteristics of syngas non-premixed flames for a bluff-body burner. The assessment of turbulent non-premixed combustion modeling techniques is presented and discussed. The simulations study the predictive capabilities of five turbulence models and are compared with the experiments of Correa and Gulati [1] for a non-premixed flame of 27.5%CO/32.3%H2/40.2%N2 and air. The Realizable k-ε and the Reynolds Stress (RSM) models were found to perform the best. Based on this, a numerical study to assess the effects of hydrogen component on syngas non-premixed combustion was performed. As a result, hydrogen addition caused the radial velocity and strain rate to decrease, which was important for mixing to decrease NO. Also, the effectiveness of nonflammable diluent mixtures, including N2, CO2 and H2O, were characterized in terms of the ability to reduce NO emission in syngas non-premixed flames. Results indicated that CO2 was the most effective diluent to reduce NO emission and H2O was more effective than N2. CO2 diluent produced low levels of OH radical, which makes CO2 the most effective diluent. Although H2O increased OH radicals, it was still effective to decrease the thermal NO because of its high specific heat.
Development of a Cyclic Pitch Turbine
Authors: Prasad Rao Jubilee , Diez F. Javier
Published: November 2015

A novel wind turbine design is proposed that increases turbine efficiency. The design consists of blades symmetrically positioned around a vertical axis. The blades experience cyclic pitch variations while rotating about the axis. The pitch variation is accomplished by an innovative mechanism that rotates the blades about a horizontal axis during rotation of the turbine. This controlled pitch variation allows the blades travelling upstream to be oriented horizontally so minimum drag is obtained. On the other hand, the blades travelling downstream are oriented vertically so maximum drag is achieved. Since the aiding downstream drag is maximum and the adverse upstream drag is minimum, this configuration allows for higher power output compared to conventional vertical axis wind turbines. Experiments on the turbine conducted in a water tunnel suggest an increase in power efficiencies.
A Computational Study of Insect Wing Cross-Sectional Geometry on Flight Performance
Authors: Feaster Jeffrey , Battaglia Francine , Bayandor Javid
Published: November 2015

The influence of cross-sectional geometry on flight performance is investigated for an insect wing using bee-like kinematics. Bee flight is of particular interest due to its mechanical simplicity, utilizing only three degrees of freedom, a high flap frequency, and mechanically linked front and hind wings. These unique flapping flight kinematics result in extremely agile flight characteristics, capable of carrying extraordinary loads relative to the bee’s weight, at a biologically capable efficiency. The performance of a corrugated insect wing and a more intuitively aerodynamic profile are compared computationally. At velocities from 1–3 m/s, the approximated cross-section is foudn to overpredict the lift generated by the corrugated profile by up to 18%. At higher velocities, 4 and 5 m/s, the approximated profile underpredicts the lift generated by the corrugated cross-section by 15%. Based upon this information the cross-sectional geometry of an insect’s wing is significant to the investigation and quantification of insect flight characteristics, for both computational analysis and future robotic applications.
Turbulent Simulations of Particle Deposition in Feline Aorta Flow for Hypertrophic Cardiomyopathy Heart Conditions
Authors: Bhushan Shanti , Borse Manish , Robinson Bryan , Walters Keith
Published: November 2015

Turbulent CFD simulations are performed for feline aorta flow to study the physiology of thrombus localization for hypertrophic cardiomyopathy (HCM) heart condition. Simulations are performed using pulsatile normal and HCM heart cardiac output velocity profiles consisting of a single peak and dual peak pattern, respectively. The predictions for the normal heart conditions are validated using experimental data. The mass outflow through the arteries compares within 1.15% of the expected values. The flow rate through the iliac artery during a cardiac cycle, and shear stress profile at infrarenal aorta cross-section also compares well with the experimental data. Most vortical structures are predicted during decreasing cardiac flow, and are located close to the renal and iliac arteries, consistent with CFD studies in the literature. The model is therefore judged to be reasonably accurate for HCM predictions. For the HCM heart conditions, outflow from all the abdominal arteries shows a trimodal pattern, with reverse flow during the secondary flow. Several vortices are predicted in the increasing secondary cardiac flow. The vortices are mostly located in the lower abdominal aorta between the renal artery and iliac trifurcation. Turbulence plays a significant role in this case, and affects flow in most of the abdominal aorta after the primary peak. Particle deposition occurs in the thoracic aorta, below the renal artery and above the trifurcation. Deposition in the lower abdominal aorta is identified due to presence of flow recirculation and low streamwise velocity.
CFD Validation Experiment of a Mach 2.5 Axisymmetric Shock-Wave/Boundary-Layer Interaction
Authors: Davis David O.
Published: November 2015

Preliminary results of an experimental investigation of a Mach 2.5 two-dimensional axisymmetric shock-wave/boundary-layer interaction (SWBLI) are presented. The purpose of the investigation is to create a SWBLI dataset specifically for CFD validation purposes. Presented herein are the details of the facility and preliminary measurements characterizing the facility and interaction region. These results will serve to define the region of interest where more detailed mean and turbulence measurements will be made.
A Geometric Preprocessor for Immersed Boundary Method Calculations
Authors: Senocak Inanc , Sandusky Micah , DeLeon Rey , Wade Derek
Published: November 2015

Computer implementation of an immersed boundary (IB) module inside a flow solver can be accomplished non-intrusively. However a versatile preprocessor is needed at the first place to extract the geometric information pertinent to the immersion of an arbitrarily complex geometry inside a Cartesian mesh. Geometric errors can negatively impact the correct implementation of the IB method as part of the solution algorithm. Additionally, the distance field from the geometry is needed to implement various turbulence models or flow initialization. Geometric processing stage for complex geometry have received less attention despite the popularity of the IB method. Our experience has shown that some of the procedures described in the literature have difficulties processing highly complex geometry or can be inflexible to implement reconstruction schemes for turbulent flows. To address these issues, we present a geometric preprocessor with a distance field solver. We constructed our procedure from computational geometry algorithms such as point-in-triangle and point-in-edge. The distance field solver uses the initial distance field at the immersed boundaries and propagates it to the rest of the domain by solving the Eikonal equation with the fast sweeping method. We demonstrate the versatility of our preprocessor for challenging test geometries from the computer graphics field, complex terrain and urban environments.
Three-Dimensional Hybrid Vortex-Immersed Boundary Method With Application to Passive Flow Control
Authors: Mimeau Chloé , Mortazavi Iraj , Cottet Georges-Henri
Published: November 2015

In this work, a hybrid particle-penalization technique is proposed to achieve accurate and efficient computations of 3D incompressible flows past bluff bodies. This immersed boundary approach indeed maintains the efficiency and the robustness of vortex methods and allows to easily model complex media, like solid-fluid-porous ones, without prescribing any boundary condition. In this paper, the method is applied to implement porous coatings on a hemisphere in order to passively control the flow dynamics.
Characterization of Turbulent Flow and Pressure Fluctuations Over a Hydrophone by LES
Authors: Bharath Aidan , Groulx Dominic , Campbell Sean
Published: November 2015

This paper presents a numerical CFD study of the turbulent flow at up to 4 m/s of water around an underwater hydrophone from the company Ocean Sonics. At such high flow rates in tidal environments, pseudo-noise, coming from turbulence induced pressure fluctuations around the hydrophone, contaminate the acoustic noise reading obtained with the device. Through the use of fine scale large eddy simulations (LES) in ANSYS Fluent, this study shows the impact of increasing flow velocities on the generated turbulence and vorticity, as well as identifying regions in the flow, and geometric aspects of the device, that are playing the larger role in pseudo-noise generation.
Spatio-Temporal Correlations of Hydrodynamic Forces on Particles in an Oscillatory Wall-Bounded Flow Environment
Authors: Ghodke Chaitanya D. , Apte Sourabh V.
Published: November 2015

Particle-resolved direct numerical simulations are performed using fictitious domain approach [1] to investigate the effect of an oscillatory flow field over a rough wall made up of a regular hexagonal pack of fixed spherical particles, in a setup similar to the experimental configuration of [2]. Turbulent flows at Reynolds numbers, Reδ = 200 and 400 (based on the Stokes-layer thickness δ) are studied. The unsteady nature of hydrodynamic forces on particles and their cross-correlations with measurable flow variables are investigated. Temporal correlations showed drag and lift to be positively correlated with a phase difference, which is approximately equal to the Taylor micro-scale related to drag/lift correlations. Spatio-temporal correlations between the flow field and particle-related quantities showed that the lift force is well correlated with the streamwise velocity fluctuations up to distances of the same order as the particle diameter, beyond which the cross correlation decays considerably. On the other hand, the pressure fluctuations are correlated and anti-correlated with the lift force in the front and aft regions of the particle, respectively, as a result of wake effects. Further statistical analyses showed that the near-bed velocity and pressure fluctuations fit poorly with Gaussian distributions. Instead, a fourth order Gram-Charlier distribution model is proposed that may have consequences on the Gaussian descriptions of sediment pick-up functions typically used in quantification of turbulent transport of sediment particles.
Numerical Simulation of Different Turbulence Models in a Compact Return Diffuser
Authors: Zhou Ling , Lang Tao , Shi Weidong
Published: November 2015

CFD have been became the main method to study the pump inner flow patterns. It is important to understand the differences and features of the different turbulence models. In this paper, the velocity flow fields in a compact return diffuser under multi-conditions are studied by CFD and PIV measurements. In the numerical simulation, three turbulence models are used to solve the steady flow filed using high-quality fine structured grids, which are including SST k-ω model, DES model and SST k-ω model with low-Re corrections. A special test rig is designed to carry out the 2D Particle Image Velocimetry (PIV) measurements, and the PIV results are used to validate the CFD results. The detailed comparison between different turbulence models and PIV results is performed. Velocity flow fields in the diffuser middle section are compared and analyzed under different flow rates. SST k-ω model with low-Re correction give a better results comparing to DES and SST k-ω model, especially have a good predication about the vortex core position under strong part-loading conditions.
A Bidirectional Valveless Piezoelectric Micropump With Double Chambers Applying Synthetic Jet
Authors: Zhang Xitong , Yang Song , He Xiuhua , Yuan Shouqi
Published: November 2015

A novel bidirectional valveless piezoelectric micropump with double chambers applying synthetic jet effect was developed. The numerical simulation was applied to study the performance and flow field of the micropump. The micropump consisted of a pump body, a cover and two piezoelectric actuators had a simple structure. The direction of the flow of the micropump could change immediately based on the Coanda effect by controlling the displacement of the two piezoelectric actuators. And the synthetic jet element increase the flowrate greatly. The effects of the Reynolds number and frequency on the flowrate were studied. The size of the throat was 200 μm × 200 μm. The Reynolds numbers were 500 and 1000 in the simulation and the SST turbulence model was chosen. The sinusoidal vibration was applied and the frequency ranged from 10 to 50 Hz. The results showed that the flowrate of jet entrainment accounted for more than 80% of the outlet flowrate. And the outlet flowrates were much larger than the volume changes of the pump chambers. The fluctuation of flowrate decreased with the increase of frequency. The micropump could achieve continuous outflow as the frequency was higher than 30 Hz.