bluuebunny/crossref_metadata_2025 huggingface dataset:
Instrumenting a Flapping Wing Air Vehicle System for Free Flight Measurement
Authors: Gerdes John , Bruck Hugh A. , Gupta Satyandra K.
Published: December 2016

Flapping wing flight is a challenging system integration problem for designers due to tight coupling between propulsion and flexible wing subsystems with variable kinematics. Due to the fluid-structure interactions present in such a system, models must be tailored to a particular design instantiation to provide high accuracy and a clear picture of underlying physical phenomena. However, a practical design approach requires an extensible model that enables exploration of several design alternatives. The difficulty of generating models that are both highly accurate and extensible suggest a combined experimental and simplified modeling approach may offer a more tractable approach to system design and integration. However, experimental data on flapping wing air vehicles that is collected in a static laboratory test or a wind tunnel test is limited because of the rigid mounting of the vehicle, which alters the natural body response to flapping forces generated. Therefore, we undertake the design of a flapping wing air vehicle system that is instrumented to provide data that may be used to create and validate a simplified aerodynamics model that is capable of freely flying. The sensor suite includes measurements of attitude, heading, altitude, position, wing angle, as well as voltage and current supplied to the drive motors. With this approach, a complete energetic picture of flight is constructed, and by varying the parameters of the vehicle, the envelope of feasible performance is investigated. Finally, the results of the experimental testing are compared to a simplified aerodynamic model to establish the effectiveness of the proposed approach to system design.
Numerical Solution of Coupled Cahn-Hilliard and Navier-Stokes System Using the Least-Squares Spectral Element Method
Authors: Park Keunsoo , Dorao Carlos A. , Fernandino Maria
Published: December 2016

We consider the least-squares spectral element method to solve the phase field model for two immiscible, incompressible and density-matched fluids. The coupled Cahn-Hilliard and Navier-Stokes system is selected as the numerical model, which was introduced by Hohenberg et al. [1]. The least-squares spectral element scheme is combined with a time-space formulation where both time and space domains are discretized by the same finite element approach to cope with time dependent multidimensional problems in an efficient way. C1 Hermite basis functions are applied for approximating the coupled system. An element-by-element conjugated gradient method is used to facilitate parallelization of the solver. The convergence analysis is conducted to verify our solver, and two numerical experiments are addressed to show applicability of the solver in general situations. Energy dissipation with conserved phase field at equilibrium state is confirmed through the bubble coalescence case, and the influence of the interface mobility is studied with the two-phase lid-driven cavity flow example.
Numerical and Experimental Analysis of Single Phase Jet Interactions
Authors: Hernandez-Alvarado Freddy , Samaroo Randy , Kalaga Dinesh V. , Lee Taehun , Banerjee Sanjoy , Kawaji Masahiro
Published: December 2016

Impinging liquid jets have many applications ranging from manufacturing processes to jet propulsion systems. In thermal applications, they are often used in atomization processes to cool the surfaces in extreme heat and mass transfer processes. In the present work, 2-D Particle Image Velocimetry (PIV) measurements have been performed to study the interaction of multiple vertical liquid jets in single-phase flow. A perforated Perspex plate with seven symmetrically placed holes was used to make the liquid jets of degassed tap water. From the PIV measurements, a wide range of liquid jet velocities were investigated, and hydrodynamic parameters such as the instantaneous velocity fields, axial (z) and radial (r) mean and RMS liquid velocities, vorticity, and in-plane Reynolds stresses have been derived. Transient 3-D CFD simulations have also been performed and compared with the experimental data. Good agreement has been found between the experimental and CFD simulations. Further, Reichardt’s hypothesis (1943) has also been examined to better understand the onset of instability for the single-phase multi jet flow.
Leading Edge Vortex Control on a Delta Wing With Dielectric Barrier Discharge Actuators
Authors: Shen Lu , Wen Chih-Yung
Published: December 2016

The interest in the active flow control based on dielectric barrier discharge (DBD) plasma actuators has increased rapidly in the past decade. Because of its features such as light weight, low power consumption, fast response and flexibility, the DBD plasma actuator is a promising technology in advancing the aerodynamic performance and maneuvering of unmanned aerial vehicles. In this study, DBD plasma actuators are employed on a full span delta wing with a 75 degree swept angle to control the leading edge vortices (LEV), which generate the vortex lift on the delta wing. The experiment is conducted in a low speed closed-loop wind tunnel and the Reynolds number based on the delta wing chord is 50,000. To fix the stagnation points, both leading edges are beveled on the windward sides at an angle of 35 degrees and actuators are insulated at the leading edges. These actuators are driven independently at a frequency of 20 kHz and a voltage of 12 kV in both continuous mode and periodic mode. The DBD actuators are calibrated using a pitot tube. Smoke flow visualization result indicates that the breakdown points of leading edge vortices can be significantly affected by DBD plasma actuators at the leading edge. In the asymmetric control case (only an actuator on one side is powered), the breakdown point of the LEV on the controlled side is greatly advanced while the one on the uncontrolled side is delayed; in the symmetric control case (actuators on both sides are powered), the control shifted the breakdown points of both LEVs further downstream. Particle image velocimetry (PIV) demonstrates clearly that the control caused by DBD actuators at the leading edge can influence the separation at the leading edges and also the shear layer vortices, which form the substructures around the primary vortices. As a result, breakdown points of LEVs are affected. Interestingly observed, the control leads to a contrary flow phenomenon: in the asymmetric case, the breakdown point of the LEV on the controlled side is advanced while, in the symmetric control case, the breakdown points of the LEV on both sides are delayed. The effects of reduced frequency and duty cycle on the control authority are also investigated experimentally. Control efficiencies of both continuous mode and periodic mode are discussed.
Profile and Mixing Losses of a Turbine Cascade Under the Condition of Low Reynolds Number Flows
Authors: Rejek Jonas , Passmann Maximilian , Hasselmann Karsten , Reinker Felix , aus der Wiesche Stefan , Mazor Lilach , Willinger Reinhard
Published: December 2016

Systematic flow measurements of profile and mixing losses were made across the blade pitches of a linear turbine cascade at low and moderate Reynolds numbers. The effect of Reynolds number on mixing behavior and development of the wake downstream of the trailing edge were investigated by means of traverse results at different planes downstream of the cascade. The experimental loss data were compared with predictions of theoretical boundary layer flow methods and of computational fluid dynamics (CFD) analyses. Several turbulence models available in commercial CFD tools and in the open CFD code OpenFOAM were considered for the present case study. It was found that substantial deviations between the numerical predictions and the experimental data occurred. These deviations may be attributed to the fact that at low Reynolds numbers, laminar and transitional boundary layer flows and flow separation phenomena became relevant. Based on the experimental two-dimensional loss data, the validity of simple Reynolds number scaling rules was assessed.
Numerical Simulation of Flow Induced by Multiple DBD Plasma Actuators
Authors: Shan Hua , Aram Shawn , Lee Yu-Tai
Published: December 2016

Active flow separation control using dielectric barrier discharge (DBD) plasma actuators oriented in the spanwise direction has been successfully investigated by the authors using an integrated numerical simulation tool that couples the unsteady Reynolds averaged Navier-Stokes (URANS) or large eddy simulation (LES) solver for incompressible flows with the DBD electro-hydrodynamic (EHD) body force model. Although many experimental and numerical investigations have indicated that the spanwise-oriented DBD plasma actuator is an effective flow control method, the application is difficult to extend from model-scale to full-scale problems, partly due to the required high amplitude and high bandwidth excitation. Also, the flow control mechanism associated with a spanwise-oriented DBD actuator is mainly direct momentum injection, therefore, the effectiveness of actuation is sensitive to the location of the DBD actuator relative to the location of flow separation. On the other hand, a few experimental studies have shown promising results using the DBD Vortex Generator (DBD-VG) consisting of multiple plasma DBD actuators oriented in the streamwise direction. By generating streamwise vortices extending a long distance downstream, the DBD-VGs enhance the mixing of the inner and outer layers of turbulent boundary layer flows. As a result, the boundary layer can better withstand an adverse pressure gradient. When applied to flow separation control, the effectiveness of the DBD-VGs should be less sensitive to location of flow separation.

The present work extends the capability of the integrated numerical simulation tool from a single spanwise-oriented DBD plasma actuator to multiple DBD plasma actuators oriented in any direction, including the streamwise direction. As a demonstration of the new capability in the DBD-URANS coupled solver, numerical simulations of flow induced by a DBD-VG actuator with an array of exposed electrodes in a quiescent environment, as well as in a turbulent boundary layer over a flat plate, are carried out. The numerical simulation successfully reproduced the longitudinal vortices embedded in the boundary layer.
CFD Simulation of a Supersonic Steam Ejector for Refrigeration Application
Authors: Su Liju , Agarwal Ramesh K.
Published: December 2016

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.
Improvement of Outlet Nozzle Shape for Pressure-Loss Reduction in Air Conditioner
Authors: Sato Daiwa , Iwase Taku , Obara Hideshi , Fushimi Naoyuki
Published: December 2016

A reduction of fan power is required to develop high efficiency air conditioner. Fan-power reduction is achieved by reducing of the pressure loss of flow channels and/or improving the efficiency of a fan. An indoor unit of the air conditioner in the present study is installed on a ceiling in a room. The indoor unit consists of a centrifugal fan, a heat exchanger, an air inlet and 4 air-outlet nozzles. One of the areas of the highest pressure-loss in the indoor unit is around the air-outlet nozzles since the cross-section of the flow channel in the air-outlet nozzles is smaller than those in other areas. In addition, the path of air flow after passing through the heat exchanger is sharply turned downward by a cabinet wall of the indoor unit. The air flow separates in the air-outlet nozzles when the air flow gets over a drain pan which receives water condensed on the surface of the heat exchanger. As a result, the effective cross-section of the air-outlet nozzles is further reduced due to the flow separation. This is main cause of the pressure-loss in the air-outlet nozzles.

The optimum nozzle shape to suppress flow separation in air-outlet nozzles of the indoor unit of an air conditioner was determined. An edge, shaped on the wall of the drain pan, minimized the flow separation by corresponding to the location between the edge and the attachment point of the flow separation. The location of the edge is defined by two parameters, and the influence of the parameters on reduction of fan power was determined by using Computational Fluid Dynamics (CFD). A CFD model of a whole indoor unit (including fan, heat exchanger, air-outlet nozzles) was applied to accurately predict fan power for different locations of the edge. Furthermore, the flow separation in the air-outlet nozzle was visualized on the basis of the CFD results. To obtain the appropriate combination of parameters to suppress the flow separation, a response surface based on the CFD results and approximate values given by a Kriging-based method, was used. The Kriging-based model is one of the response-surface methods and is characterized by approximating a nonlinear function based on Bayesian probabilistic estimation. The response surface provided the area containing the appropriate parameters for reducing fan power (“parameter area”, hereafter). The parameter area of fan-power reduction on the response surface was found. The CFD results confirm that the flow separation corresponds to the edge location given by this parameter area and that the edge minimizes the flow separation. To experimentally verify the effect of the edge on fan-power reduction, four points in the parameter area for fan-power reduction were selected, and four nozzle shapes with these parameters were prototyped. It was found that fan power was reduced (at most) by 9.9% by the optimized nozzles shapes in comparison with the current shape of air-outlet nozzles.
Study of a Bionic Anti-Erosion Blade in a Double Suction Centrifugal Pump
Authors: Qian Zhongdong , Dong Jing , Guo Zhiwei , Wang Zhiyuan , Wang Fan
Published: December 2016

A bionic blade with convex domes was applied in a double suction centrifugal pump to improve erosion resistance of the blade surfaces in this study. The hydraulic performance of the pump was simulated and the numerical results were in good agreement with the experiment data. The erosion rates of the smooth blade and bionic blades with convex domes at different heights (1.0 mm, 1.5 mm, 2.0 mm ) were numerically predicted. The results showed that the pump with bionic blades had a higher head and a lower efficiency than those of the pump with smooth blades. A comparison of the erosion rates indicated that the bionic blades exhibited much better erosion resistance than the smooth surface ones. The high erosion-rate area was reduced remarkably and the erosion region became more dispersed on the whole bionic blade surface. The pressure side of the blade with 2.0 mm-height convex domes showed better anti-erosion performance than those with other two heights, while the suction side with 1.0 mm-height domes showed better anti-erosion performance.
Analysis for Cooling Circuit of High Speed Rescue Pump Based on Flow-Heat Coupling
Authors: Bai Yuxing , Kong Fanyu , Xia Bin , Liu Yingying
Published: December 2016

In order to meet the requirement of coal mine flooding emergency rescue, a high power, high head and small volume high-speed wet submersible pump is designed. The high speed rescue pump applies the wet motor and pump integrated structure to achieve the best effect . When high speed rescue pump works, the temperature rise of the motor is high, which may cause the damage of the whole unit if the heat which produced by motor can not be taken away fully. The design of the cooling circuit is critical for the performance of the high speed rescue pump. This paper gives two design methods of the cooling circuit of high speed rescue pump. The design performance parameters: Capacity Q = 200m3/h, Head H = 50m, Rotate speed n = 6000r/min, Power P = 600kW. Two cooling circuits contains the normal and reverse one, which are based on theoretical deduction, numerical simulation and experimental verification. First and foremost, two theoretical models of cooling circuit are established by the theory of convective heat transfer .The heat balance and distribution are calculated by theoretical derivation. Then, both three-dimensional models of the circuit are built by CREO and simulated by ANSYS. The method of flow-heat coupling is used to simulate the whole inner flow field of the high speed rescue pump at different running conditions by considering the transformation of thermal performance parameter of cryogenic fluid caused by temperature change. In the simulation ,the information , such as temperature , flow field, pressure distribution of the whole cooling circuit together with temperature and velocity in the gas gap where temperature changed greatly, the convective heat transfer between fluid and motor ,and the flow rate of the cooling fluid are also gained. The analysis results show that: from the comparison of the pressure distribution of the two cooling forms, under the same inlet and outlet liquid condition ,the minimum and maximum pressure value of the reverse circuit are much higher than the corresponding value ,which means the reverse cooling method is better than the normal method as the aspect of cavitation performance. The temperature rise of reverse cooling circuit with the value 1.5K is smaller than the value of the normal cooling circuit. As the key part of the cooling circuit, the motor gas gap has a significant influence on the performance of the circuit. The velocity and temperature distribution is given to study the law of the flow and thermal field in the gap which can supply an intuitive understanding of the key part. At last, an experiment of a model pump is carried out on the test table validated the reliability of the reverse cooling circuit. It can be also concluded that the cooling circuit can satisfy with mode demand of the working condition of the high speed rescue pump.
Numerical Simulation and Performance Prediction of Multistage Canned Motor Pump
Authors: Xia Bin , Kong Fan-Yu , Bai Yuxing , Duan Xiaohui
Published: December 2016

Due to the advantages of high head and no leakage, multistage canned motor pump is widely used in oil industry, chemical industry, national defense and atomic energy. In order to meet the needs of the market, the multistage canned motor pump is designed. This paper introduced the hydraulic design and structural design. In order to optimizing the performance of the pump, this paper designed and used multistage canned motor pump DBP15–50×8 as the research object. Three-dimensional model of the main flow passage components is built and the mesh is generated respectively by using Pro/E and ICEM software, and we calculated the whole internal flow field of the pump that was selected by using ANSYS CFX14.0 software, achieving the pressure and velocity distribution in the pump and the internal details of flow in impeller and other main flow components. The post-processing showed the fluid in sliding bearing section rotates around the shaft, so the local flow is disorder. The comparison of the performance prediction and the experiment shows that the error is low. The cavitating turbulent flow in the flow field was numerically simulated by using the cavitation model. The cavitation phenomena didn’t occur in the experiments. The condition meets the result of numerical simulation.
A Study of 3-Dimensional Reattachment on Rotor Blades After Dynamic Stall
Authors: Raghav Vrishank , Hiremath Nandeesh , Komerath Narayanan
Published: December 2016

Stereoscopic Particle Image Velocimetry data from a 2-bladed rigid NACA0013 rotor undergoing retreating blade dynamic stall in a low-speed wind tunnel, are analyzed to understand the phenomenon of 3-dimensional reattachment at the end of the dynamic stall cycle. Continuing from prior studies on the inception and progression of 3-D rotating dynamic stall for this test case, phase-resolved, ensemble-averaged results are presented for two values of rotor advance ratio at two spanwise stations along the blade. The results show the nominal reattachment getting delayed in rotor azimuth with higher advance ratio. At low advance ratio reattachment starts at the leading-edge and progresses towards the trailing-edge with a vortex shedding transporting excess vorticity sheds from the leading-edge and convects away, with the flow reattaching behind it. At higher advance ratio, the vortical structure shrinks in size while the flow close to the trailing-edge appears to reattach. Spanwise vorticity transport appears to be the mechanism. The difference could be attributed to the lower chordwise velocity of the blade at higher advance ratio, bringing in a rotation effect.
Influence of Inclination Angle on Intermittent Two Phase Flows
Authors: Escrig Escrig Josep , Hewakandamby Buddhika , Dimitrakis Georgios , Azzopardi Barry
Published: December 2016

Intermittent gas and liquid two-phase flow was generated in a 6 m × 67 mm diameter pipe mounted rotatable frame (vertical up to −20°). Air and a 5 mPa s silicone oil at atmospheric pressure were studied. Gas superficial velocities between 0.17 and 2.9 m/s and liquid superficial velocities between 0.023 and 0.47 m/s were employed. These runs were repeated at 7 angles making a total of 420 runs.

Cross sectional void fraction time series were measured over 60 seconds for each run using a Wire Mesh Sensor and a twin plane Electrical Capacitance Tomography. The void fraction time series data were analysed in order to extract average void fraction, structure velocities and structure frequencies.

Results are presented to illustrate the effect of the angle as well as the phase superficial velocities affect the intermittent flows behaviour. Existing correlations suggested to predict average void fraction and gas structures velocity and frequency in slug flow have been compared with new experimental results for any intermittent flow including: slug, cap bubble and churn. Good agreements have been seen for the gas structure velocity and mean void fraction. On the other hand, no correlation was found to predict the gas structure frequency, especially in vertical and inclined pipes.
Friction Factor of Silicon Dioxide-Water Colloidal Suspension Flow in Circular and Square Tubes
Authors: Sharif Md. Tanveer , Pant Sarbottam , Tang Clement C.
Published: December 2016

The present study focuses on the friction factors of a colloidal suspension flow in circular and square tubes. The colloidal suspension was made of silicon dioxide nanoparticles dispersed in distilled water at a concentration of 9.58% by volume. The viscosity and shear stress of the suspension were measured and it was found that the fluid exhibited non-Newtonian behavior. The rheological behavior of the suspension could be adequately modeled as a power-law generalized Newtonian fluid (GNF). When the consistency and the flow behavior indices of the suspension were properly evaluated, the friction factors of the suspension flowing in tubes with circular and square cross-sections exhibited similarities with those of Newtonian fluid flow. In fully-developed laminar flow, the Poiseuille number for the suspension was similar to that for a Newtonian fluid flow. In turbulent flow, the Dodge and Metzner’s relations for the friction factor and a generalized Reynolds number can be used to adequately describe the suspension in turbulent flow. Observations from the friction factor measurements showed that the onsets of transition to turbulent flow vary with the cross-sectional shape of the tube and differ from those of Newtonian fluid flow. This might suggest that the cross-sectional shape of the flow passage and the presence of nanoparticles could affect the onset of transition to turbulent flow for the suspension.
Parametric Study of Erosion Under High Concentrated Slurry: Experimental and Numerical Analyses
Authors: Mahdavi Marzieh , Karimi Soroor , Shirazi Siamack A. , McLaury Brenton S.
Published: December 2016

Highly concentrated slurries are found in many different industrial and environmental applications, such as hydro-transport systems of the oil sands industry, drilling and fracturing applications, and stirring vessels. When the volume fraction of particles is low, particles have little influence on the structure of the flow. However, even when average concentration is relatively low, there can still be some regions of high concentration. In highly concentrated flows, the effect of particles on the dynamics of the flow cannot be neglected. Under this condition, particle concentration can affect the turbulence intensity and erosion ratio.

Several experiments have been conducted to examine the effect of different parameters on erosion. Different models have been developed to predict erosion ratio in liquid and gas flows. However, previous studies mostly have examined dilute slurries and less attention has been paid to the effect of high concentration of particles on erosion. In this study, the erosion due to highly concentrated slurries is investigated using both experimental and numerical approaches. There are several parameters such as particle properties and shape, target material, fluid properties and dynamics of the flow that affect erosion ratio. In addition, higher fluid viscosity can significantly affect the flow dynamics and change the interaction behavior between fluid and solid particles.

Effects of particle size and velocity on erosion ratio are investigated for different sand concentrations. Experiments have been conducted for various concentrations, ranging from 1% to about 20% by mass and two different particle sizes, 75 μm and 300 μm. Erosion ratio was calculated based on two different approaches, mass loss and volume loss obtained from 3-D profilometry data. Scanning electron microscope (SEM) images were obtained for 1% and 15% concentration cases to examine the erosion on different parts of the specimens. In addition to the experimental work, a CFD model is setup to simulate the erosion results. The aim of this CFD simulation is to predict erosion rate of the specimen caused by submerged slurry jet flow by using Reynolds stress as turbulence model. The fluid flow solution is obtained using an Eulerian approach and a Lagrangian scheme is used to track the sand particles. In these models, the injected particles from the inlet impact the target wall in order to investigate the erosion.
Numerical Simulation of Insulin Depot Formation in Subcutaneous Tissue
Authors: Zedelmair Michael M. , Mukherjee Abhijit
Published: December 2016

In this study a numerical model of the insulin depot formation and absorption in the subcutaneous adipose tissue is developed using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. A better understanding of these mechanisms can be helpful in the development of new devices and cannula geometries as well as predicting the concentration of insulin in the blood. The injection method considered in this simulation is by the use of an insulin pump using a rapid acting U100 insulin analogue. The insulin is injected into the subcutaneous tissue in the abdominal region. The main composition of the subcutaneous tissue is blood vessels and adipose cells surrounded by interstitial fluid. The numerical simulation is conducted in a 2D-axisymmetric domain where the tissue is modeled as a fluid saturated porous media. Due to the presence of channel formation in lateral direction in the tissue, an anisotropic approach to define the permeability is studied having an impact on the viscous resistance to the flow. This configuration is resulting in a rather disk shaped depot following recent experimental findings. The depot formation is analyzed running Bolus injections ranging from 5–15 Units of insulin corresponding to 50–150μl. The depot formation model has been extended implementing the process of absorption of insulin from the depot to be able to run the simulation over longer timeframes where absorption starts playing an important role.
Dynamics and Propulsive Efficiency of Bio-Inspired Undulatory Marine Locomotion
Authors: Gater Brittany , Feaster Jeffrey , Bayandor Javid
Published: December 2016

Computational fluid dynamics (CFD) was used to investigate the fluid mechanics for undulatory stingray locomotion. This method of undulatory propulsion can be utilized to generate non-turbulent thrust with minimal disturbance to the immediate environment, ideal for exploratory vehicles for underwater environments. Undulatory locomotion was modeled as a two-dimensional fin in free flow with a deforming non-slip boundary to represent a propagating sinusoidal wave with a linearly increasing amplitude, constant frequency, wavelength and flow velocity. In the presented computational study, we varied the amplitude, wavelength, frequency, and flow velocity parametrically and examined the effect on thrust, lift, and pitching moment. Average net thrust was found to increase with wavelength and frequency, whereas for this two-dimensional case amplitude showed negligible effects. For the parametric cases, a theoretical efficiency for forward propulsion was then calculated for a continuous fin. The amplitude was found to increase the input power required for actuation, but decreased output power for forward thrust. Variation of the other parameters showed that the output power depends nearly linearly on the input power, regardless of the particular kinematics or swimming speed.
Adaptive-Time-Step High-Frame-Rate Particle Image Velocimetry
Authors: Nedyalkov Ivaylo , Wosnik Martin
Published: December 2016

With the availability of high-frame-rate (HFR) PIV systems, it is possible to capture time series of particle images at rates which can exceed the necessary frequency to temporally resolve essential flow. In this case, some of the recorded frames can be skipped, in order to obtain an adequate time step between two images, leading to favorable values for pixel displacement. In this paper a technique for decreasing pixel locking in complex flows based on an adaptive time step processing procedure is proposed. If PIV data are taken at much higher frequency than needed, the processing can be repeated for multiple time steps, ensuring the optimal pixel displacement for every interrogation spot. A smaller time step is used for large velocities and larger time steps are used in the areas of low velocity. To illustrate this technique, a sample data set was acquired of the flow on the suction side and the region just downstream of a NACA 0015 hydrofoil at a high angle of attack (16 degrees), ensuring a wide range of velocities within the PIV field of view. The experiments were performed in the University of New Hampshire High-Speed Cavitation Tunnel – HiCaT, at a comparatively low speed (2 m/s) in order to increase the range of possible time steps for post processing. HFR PIV data were obtained at 1800 frames per second for a field of view of approximately 100 mm × 100 mm. The data were processed multiple times, each time skipping between 0 and 19 frames, resulting in time steps between 1 to 20 times of the original time step between two images. As expected, there is a significant difference between the results for mean velocities with different time step processing, most notably in the region of the suction side of the foil. The RMS velocity fields also show a similar trend. In order to obtain a more accurate representation of the mean flow, the data for each interrogation spot were combined based on the pixel displacement values. The resulting velocity field was compared to that obtained with single-time-step PIV. A “map” was created showing what time step was selected for each interrogation spot. Suggestions were made on what time steps should be selected for the post processing in order to decrease the post processing computational time. A discussion was provided on the feasibility of using the technique for instantaneous velocity fields. Using ATS PIV may be beneficial in flows where both large and small velocities are of importance, e.g., flows with separation.
Wingtip Devices for Tidal Turbines: Performance Improvement and Cavitation Mitigation
Authors: Nedyalkov Ivaylo , Gagnon Ian , Shull Jesse , Brindley John , Wosnik Martin
Published: December 2016

Wingtip devices are common in aeronautical applications and are increasingly used on wind turbines. However, their use in hydrokinetic energy conversion applications such as tidal turbines to date is minimal, due to the concern for increased bio-fouling and also the fact that there is little or no data publically available describing their cavitation characteristics. In this study, three wingtip designs were considered for hydrokinetic turbine applications: a plain foil with a rounded tip (considered the reference case), a generic wingtip device (a winglet), and a novel “split-tip” device. The tips were studied numerically and experimentally at different angles of attack. The numerical simulations were performed in OpenFOAM using the k-omega SST model to predict the lift and drag characteristics of a “base” foil with each of the three wingtip devices. Additionally the pressure and vorticity were observed. Experiments were conducted in the University of New Hampshire High-Speed Cavitation Tunnel – HiCaT. A modular experimental test bed with an elliptical foil section was developed specifically for the study. The test bed extends to the centerline of the tunnel where wingtips are attached, and has four small-diameter tube openings to accommodate pressure measurements and/or mass injection studies. Water tunnel data were obtained for lift, and cavitation inception, and compared to the numerical simulations. The numerical results show decreased vorticity with presence of the wingtip devices, however, the advantage of using wingtips for decreasing drag and increasing lift forces is not conclusively exhibited. The experimental measurements suggest that there is a significant suppression of tip vortex cavitation with the use of wingtip devices at high angles of attack (around 10 degrees), but the advantage of using the wingtip devices diminishes at lower angles of attack.

It was shown by Arndt [1] that tip-vortex cavitation on hydrofoils can be related to the lift coefficient and the Reynolds number, where the cavitation index at inception is proportional to the square of the section lift coefficient and the Reynolds number based on hydrofoil chord, taken to the power m. The power exponent m has been generally accepted to be approximately 0.4. This relation is made into an equation via a coefficient of proportionality K, which depends on the wingtip and foil section geometry, and has been empirically determined to have values between 0.025 and 0.056 for previously investigated wings. While the value of the coefficient K for the reference wing tip remained comparatively constant for the range of conditions investigated (angles of attack, Reynolds numbers), it varied significantly for the foil terminated by the winglet. This may be due to the non-elliptical load distribution in the span-wise direction, but also raises the question whether the standard tip-vortex cavitation correlation for hydrofoils is applicable for general wingtip devices.
Validation of a Time Dependent Physio-Chemical Model for Thrombus Formation and Growth
Authors: Hosseinzadegan Hamid , Tafti Danesh K.
Published: December 2016

In this study, a shear-dependent continuum model for platelet activation, adhesion and aggregation is validated using computational fluid dynamics (CFD). To take the presence of red cells into account, a combination of excess-platelet boundary layer and enhanced mass diffusivity of platelets and large species is used to mimic this behavior. The model has been validated under three different shear conditions and two different heparin levels. Also three-dimensional simulations were carried out to evaluate the model’s prediction of thrombus growth rate for stenosed tubes under various flow conditions and stenosis degrees. For these cases, also the effect of change in platelet diffusivity has been investigated by using an empirical correlation for enhanced diffusivity of platelets. For all 3D simulations, results for thrombus growth rate as a function of local wall shear rate were compared to those of experiments and numerical studies in the literature and an acceptable agreement was achieved.
Analyses of Pressure Fluctuation and Fluctuation Reduction of an Automobile Fuel Pump
Authors: Zhang Lu , Wu Peng , Wu DaZhuan
Published: December 2016

The automobile fuel pump studied in this paper is a mini regenerative pump consisting of a casing with an axial channel and an impeller with 33 radial blades. In this study, the pressure fluctuation characteristics of the regenerative pump were analyzed with the method of unsteady CFD analysis. To investigate the pressure fluctuation, the unsteady Reynolds-averaged Navier-Stokes equations (URANS) were solved with realizable k-ε turbulence model using the CFD code FLUENT. To study the effect of arc length of stripper on the pressure fluctuation, the pressure fluctuations at several locations of pumps with strippers of different arc length were analyzed in time and frequency domain. The static pressure contours at different times were presented to reveal the generating mechanism of pressure fluctuation of the regenerative pump. For the purpose of pressure fluctuation reduction, a random modulation of blade spacing method was applied to design a new impeller with uneven spaced blades. The pressure fluctuations of four different pump units of the combination of different blade distribution impellers with casings of different arc length of stripper were studied and discussed. The pressure fluctuation of the pump unit of combination of random blade distribution impeller and large arc length stripper is significantly reduced. In this paper, the generating mechanism of pressure fluctuation for regenerative pump is uncovered, and a good solution to the fundamental pressure fluctuation reduction of regenerative pump is put forward.
Application Building in Undergraduate Courses With a Simulation Component
Authors: Milanovic Ivana , Eppes Tom
Published: December 2016

The undergraduate engineering curriculum at our institution is replete with both problem-based and project-based learning components. This paper focuses on the third and most complex methodology needed to prepare students for a successful career in engineering: inquiry-based learning (IBL). With IBL, students learn with the aid of mentoring how to develop and answer a research question. However, IBL requires a significant time-investment, both in and outside the classroom. This is one of the teaching challenges within lecture-based thermo-fluids courses, where the coverage of required material does not allow much time for both IBL and development of field-specific simulation skills. Additional challenges include the reliance on mathematical tools that often hamper student understanding of the underlying phenomena and difficulty in providing immersive and exciting visuals that support in-depth learning.

An IBL component was incorporated into a simulation-based design in two successive junior year courses: fluid mechanics and heat transfer. Both courses were modified to contain scaffolded and contextualized simulations with application building that develop: (a) technical competency by developing modeling skills, (b) deeper understanding of thermofluids by solving realistic technological problems, and (c) writing skills by producing technical reports for each simulation.

Companies are increasingly using simulation applications to extend the benefits of product and process models beyond engineering to other internal business functions such as manufacturing, product development, and sales technical support. Applications involve creating a simplified interface that still contains the full efficacy of the underlying model without having to expose the end user to its complexity. An ‘Application’ building component adds a new skillset that further strengthens our program graduates.

Consequently, supported by mentoring, students now integrate prior skills into an independent research initiative. They propose, plan and execute a design that is of their interest, relevant to the course topics, and suitable in rigor. In parallel with skillset and technical knowledge building, strategies and resources are introduced to engage students in a research topic of their choosing. This process includes preparing a statement of work, reviewing relevant literature, completing a technical study, and documenting the results. The results to date are presented along with some examples of student projects.
Analysis of Bloodstains Patterns at Sharp Impact Angles
Authors: Moshfeghi Mohammad , Rahimipetroudi Iman , Hur Nahmkeon
Published: December 2016

Bloodstain pattern analysis is of tremendous value for the investigation of the evidence at the crime scene. Analyzing the bloodstain patterns provides an appropriate method for retracing the origin of blood droplets and also reconstruction of the crime scene. The patterns of the bloodstains on the floors and walls are determined by the impact conditions of blood drops such as droplet sizes, impact angles and velocities. The objective of this work is to study the bloodstain patterns on an inclined surface, in order to categorize the bloodstain shapes. The experiments have been carried out using a 38% glycerol solution at room temperature between 16° C∼21° C. The experiments have been done for three different droplet diameters, five different velocities and four different surface inclinations. The blood-mimicking fluid viscosity and density have been measured at the same temperature range with the experiments. The results have been investigated in terms of bloodstain shape and patterns and three different categories have been determined. In addition, a new mathematical formula has been derived based on the equivalent diameter of the bloodstains, which relates the bloodstain dimensions to the droplet Reynolds and Weber numbers. It has been shown that the proposed formula fits more accurately with the experimental results for high impact angle cases as compared to the classical formula.
Convective Flow and Heat Transfer Inside a Beta Type Stirling Engine Based on Control Volume Finite Element Method
Authors: Gheith Ramla , Hachem Houda , Zahi Nessrine , Aloui Fethi , Ben Nasrallah Sassi
Published: December 2016

In this manuscript, a beta type Stirling engine is numerically modulated. The flow and heat transfer characteristics are finely considered in each engine compartment. The PV diagram is plotted to determine the produced work by the engine. The instantaneous temperature in compression and expansion spaces present a larger variations that recorded in all treated heat exchangers. It is observed that the porous media dumps the oscillations. The temperature evolution is plotted for 100 successive Stirling cycles in order to observe its stability in each Stirling compartments. During the first 10 cycles, the regenerator temperature is influenced by the cold flow pumped by the cooler. It reaches thermal equilibrium after only 10 cycles. From this point, the regenerator temperature undergoes a slight increase to stabilize at 1.05 * Ta.
Correlated Bias Uncertainty in PIV Data due to Interrogation Window Overlap
Authors: Cressall Rick , Smith Barton L.
Published: December 2016

Vorticity fields calculated from PIV data have previously been shown to be sensitive to interrogation window overlap and differentiation scheme. To date, only qualitative comparisons have been made since a quantitative study requires knowledge of the “true” velocity. A data set consisting of several simultaneous measurements of both high fidelity and more typical PIV data is used for the present study. The uncertainty of the high fidelity data is small enough compared to the typical data to be considered “truth”. This allows a quantitative measure of correlated error due to interrogation region overlap and how it decreases with distance. Two similar differentiation schemes that are known to produce qualitatively different vorticity fields are also examined. The net effects of correlation are shown to decrease random uncertainty in most cases.
Noninvasive quantitative estimation of hepatic steatosis by ultrasound: a comparison of the hepato-renal index and ultrasound attenuation index.
Authors: Kwon Heon-Ju , Kim Kyoung Won , Jung Jin-Hee , Choi Sang Hyun , Jeong Woo Kyoung , Kim Bohyun , Song Gi-Won , Lee Sung-Gyu
Published: December 2016

Aims: To compare the accuracy of the ultrasound attenuation index (USAI) and hepato-renal index (HRI) for the diagnosis of hepatic steatosis (HS). Material and methods: Two hundred and twenty-four potential living hepatic donors underwent US and subsequent US-guided liver biopsy. The USAI was calculated from US images with an 8 MHz transducer and HRI was measured on sagittal images with a clear visualization of both the liver and kidney. Using histological degrees of HS as the reference standard, we compared the performance of USAI and HRI for diagnosing HS ≥ 5% and ≥ 30% by receiver operating characteristic curve analysis. The interobserver agreement was evaluated by using intraclass correlation coefficients (ICCs) or Bland–Altman statistics. Results: Histologic degree of HS was 0–70% (median, 5%). HRI showed a tendency towards higher accuracy than USAI for diagnosing HS ≥ 5% (the area under the ROC curve, 0.856 vs. 0.820; p= 0.279) and ≥ 30% (0.937 vs. 0.909; p = 0.378) without statistical significance. There was an excellent interobserver agreement for both USAI and HRI (ICC = 0.931 and 0.973, respectively). According to the Bland–Altman method, the 95% limits of difference between two readers for HS were −8.5% to 6.6% by USAI and −4.8% to 6.2% by HRI. Most patients would have the difference of calculated HS by USAI (74.0%) and HRI (96.0%) from different operators within a range of ±5%. Conclusions: Although statistically insignificant, HRI was superior to USAI for the diagnosis and quantitative estimation of HS in terms of diagnostic performance, including accuracy and reproducibility.