bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow-Field in a Linear Vane Cascade With Endwall Fillet and Film-Cooling
Authors: Mahmood Gazi I. , Arnachellan Keenesh
Published: October 2018

Fillets at the junction of blade and endwall are employed to passively control the endwall secondary flows and total pressure losses in the cascade flow-field investigations. Film-cooling of the endwall using the slots at the entrance of blade passage is also investigated in the cascade setup to actively control the flow-field. The present paper reports the experimental measurements of the flow-field in a linear vane cascade that employs the endwall fillet and film cooling flow. The objectives are to investigate the additional effects of the film-flow on the secondary flows and total pressure losses in the cascade when the fillet is present. The fillet is employed at the vane-endwall junction from the leading edge to the throat region of the cascade passage. The film-cooling flow is provided from two slots located at the entrance of vane-passage simulating the platform gaps between the rotor/stator or combustor/NGV (nozzle guide vane) discs in the gas turbine. The vane-profile and cascade geometry are obtained from the first-stage of the GE-E3 gas turbine engine. The inlet Reynolds number based on the actual-chord of the vane is 2.0E+05. The inlet blowing ratio of the film cooling flow is varied between 1.1 and 2.3 as the density ratio of the film-flow to mainstream remains constant at 1.0. As the cascade is housed in an atmospheric wind tunnel, the measurements are obtained in the incompressible flow regime. The measurements include the distributions of endwall pressure, flow angles, axial vorticity, and total pressure losses along the vane passage. The results indicate the flow yaw angle and axial vorticity in the filleted passage without the film-cooling are reduced in the endwall region compared to the baseline case (no fillet and film cooling). Consequently, the passage vortex, which is the primary secondary flow, is weakened reducing the total pressure losses in the filleted passage. As the film-cooling flow is introduced in the filleted passage, the yaw angle in the endwall region is reduced further weakening the pitchwise-flow responsible for the development and strengthening of the passage vortex. The total pressure losses are also reduced further with the film-cooling flows and with the increasing blowing ratios. The film coverage of the endwall will be better as the passage vortex is weakened in the filleted passage. The present investigation is important for reducing the aerodynamic losses and improving of the film-cooling effectiveness in the gas turbine cascade.
Coherent Structures of Tornado-Like Vortices
Authors: Karami Mohammad , Carassale Luigi , Hangan Horia , Refan Maryam
Published: October 2018

Tornado-like vortices have distinctive characteristics that make them significantly different from atmospheric boundary flows. These dynamic characteristics are highly turbulent and unsteady which make them very complex. In this paper, it is tried to identify these dominant patterns, known as coherent structures, out of tornado-like vortex. These vortices are experimentally simulated in a 1/11 scaled model of WindEEE Dome at Western University.

Coherent structures provide simplified but physical understanding of the flow. The classical method for extraction of coherent structures is proper orthogonal decomposition (POD) method. However, there are serious concerns about POD as it has orthogonality constraint. Thus, we applied another method called independent component analysis (ICA) which does not have orthogonality restrictions. This method helped us to identify non-physical POD modes and to provide a better physical description of the flow.
Evaluation of Performance and Code-to-Code Variation of a Dynamic Hybrid RANS/LES Model for Simulation of Backward-Facing Step Flow
Authors: Shobayo Olalekan O. , Walters D. Keith
Published: October 2018

Computational fluid dynamics (CFD) simulation results are presented for the canonical test case of flow over a backward facing step (BFS). The BFS case exhibits complex physics including turbulent separation, reattachment, and boundary layer restart. Results are obtained using two different turbulence models as representative examples of two classes of modeling: Reynolds-averaged Navier-Stokes (RANS) and hybrid RANS-LES (large-eddy simulation). The specific models used are k-ω SST and dynamic hybrid RANS-LES (DHRL). The objective of the study is to compare the performance of both turbulence models as implemented in three different flow solvers (Flow Psi, Loci-CHEM, and Ansys FLUENT) and using three different methods for numerical discretization of the convective terms in the governing equations. Results are compared to experimental data for validation purposes. Results show that both k-ω SST and DHRL models are capable of reproducing the mean flow physics with reasonable accuracy. The differences due to solver algorithm and convective discretization scheme are apparent for both models, but the DHRL model shows more sensitivity, as expected. Overall the results highlight the importance of considering all integrated aspects of a turbulent CFD simulation to ensure that an optimum combination of model and numerical method are employed.
Effects of Blade Configuration on the Performance of a Feed Pump
Authors: Kang Can , Gu Yiping , Ding Kejin , Zhang Wenbin
Published: October 2018

The emphasis of the present study was placed on the impeller of a centrifugal feed pump. A comparative investigation was implemented between three impeller schemes, one with ten equal-length blades and the other with five long and five short blades. Numerical simulation was performed to investigate the flow field associated with the three schemes. Flow patterns were considered. Pressure fluctuations at the impeller outlet and the volute channels were monitored. The validity of the numerical approach was proved with a comparison between experimental data and the numerical result for the scheme with equal-length blades. The results show that the relative deviation of pump head is less than 5% between the three impeller schemes. Meanwhile, the pump efficiency manifests a slight difference. The improvement of flow quality in the impeller eye area is accomplished as half of the blades are shortened. For the scheme with equal-length blades, the pressure fluctuations with the blade passing frequency are distinct both at the impeller outlet and in the volute channels. In comparison, the schemes with five long and five short blades are characterized by weakened blade passing frequency. Low-frequency components are excited remarkably for the two impellers with long and short blades. The pros and cons of the scheme with long and short blades are explained.
Forecasting Optimal Time-of-Arrival for Carrier Landings Using Prior Ship Motion
Authors: Vorwald John , Schwartz Alan , Kent Christopher , Nguyen Phong
Published: October 2018

Sea-based aviation operations, such as carrier launch / recovery of aircraft, can be limited or interrupted by ship motion. Such operations may benefit from real time ship-motion forecasting, particularly in sea states above SS6, as unanticipated large motions may suddenly occur. Ship motion forecasting was optimized using an autoregressive moving average vector (ARMAV) model. The forecasting was accurate for approximately 25 seconds with accuracy evaluated using either correlation coefficient or root mean square error metrics. The ship motion data evaluated was simulation data generated by a ship motion prediction program for a generic CVN hull.
Experimental Investigation of Flow Behavior in a Bend and Sand Erosion Pattern Under Single-Phase and Multiphase Flow Conditions
Authors: Zahedi Peyman , Asgharpour Alireza , Khanouki Hadi Arabnejad , McLaury Brenton S. , Shirazi Siamack A.
Published: October 2018

Solid particle erosion in pipe fittings may cause pipe failure and major safety and environmental issues. Elbows are widely used in oil and gas production and transportation systems, and they are one of the most vulnerable fittings when presence of sand particles is anticipated in the system. An experimental apparatus was created to investigate the flow behavior in a 4-inch 90 degree bend under multiphase flow conditions in both horizontal-horizontal and vertical-horizontal elbow orientations. It was observed that in vertical annular flows, entrained droplets and liquid film are focused at the center of the outer bend, and as liquid velocity increases, the liquid film inside the elbow outer radius becomes thicker and it decreases the measured erosion. Observations were verified by comparison of erosion magnitudes in bends for different liquid velocities obtained utilizing a state-of-the-art ultrasonic thickness measurement technique. Erosion patterns and location of maximum erosion results were also examined through paint erosion experiments. It was concluded that regardless of particle size and gas and liquid flow rates, maximum erosion occurs in the range between 40° to 50° on the bend for gas dominant flows in low pressure gas environment studied here. A secondary erosion pattern caused by particle rebounds was observed to occur in the range between 60° to 90° in the bend. Erosion experimental results in the 4-inch elbow were compared with Computational Fluid Dynamics (CFD) predictions of erosion, and agreement was observed in terms of erosion pattern and 40% agreement in magnitude.
Utilization of Machine Learning to Predict the Surface Tension of Metals and Alloys
Authors: Nieto Zackery , Kotteda V. M. Krushnarao , Rodriguez Arturo , Kumar Sanjay Shantha , Kumar Vinod , Bronson Arturo
Published: October 2018

As technology progresses, predictive solutions created by computer generated algorithms are becoming more and more viable. The purpose of this study is to test the predictive capabilities and their values of three different types of predictive algorithms, a multi-variable linear regression algorithm, a nonlinear random forest model, and a TensorFlow deep learning neural network model. To compare each algorithm, we used the surface tensions of the molten pure metals, copper, bismuth, and silver, as well as the copper-bismuth, and copper silver molten alloys. The surface tensions were then compiled into data sets meant for training and testing the algorithms predictive capabilities. Throughout this study, we considered how each algorithm could be corrected in ways to increase its predictability without over-constraining the algorithm to satisfy only these data sets. At the end, it became apparent that although the predictions of each algorithm were able to get to a fairly decent accuracy, the random forest model proved to be the best and most useful algorithm for surface tensions.
Predicting the Depth of Penetration of Molten Metal Into a Pore Network Using TensorFlow
Authors: Schiaffino Arturo , Kotteda V. M. Krushnarao , Bronson Arturo , Shantha-Kumar Sanjay , Kumar Vinod
Published: October 2018

Liquid metal infiltration consists of infusing liquid metal into a porous media or a packed bed of boron carbide powder to react and create ultimately a metal or ceramic matrix embedded with boride-carbide precipitates. The purpose of the study is to model the liquid flow into the capillaries of the packed bed by using machine learning algorithms from an open source available as TensorFlow library created by Google Brain. The library has a variety of algorithms including training and inference algorithms forming deep neural network models to predict the wetting dynamics, flow resistance, and the depth/rate of penetration into the capillaries of the packed bed. In the present work, the results from the machine-learning python code based on the TensorFlow library is compared against the experimental data obtained for molten Hf-Ti-Y-Zr alloys infiltrating into a packed bed of boron carbide at temperatures up to 2300°C. A summary of the techniques used to tweak the machine learning algorithms to predict the infusion behavior will be presented.
Effects of Offset Height on the Turbulent Characteristics of Rectangular Twin Jets
Authors: Nwaiwu Chidiebere F. , Tachie Mark F. , Agelin-Chaab Martin
Published: October 2018

Turbulent characteristics of a twin jet were experimentally investigated for offset heights, h = 1d and 3d where d is the nozzle diameter. The experiments were conducted using a pair of rectangular nozzles of an aspect ratio of 3, that is oriented in the minor plane and with a nozzle separation ratio of 2.3. The Reynolds number, based on jet exit velocity and nozzle diameter was maintained at 4622. The results show that confinement effect decreased the merging point of the jets by 30% but there is no significant effect on the combined points. Reduced confinement showed an 89% reduction in the acceleration of the mean streamwise surface velocity. Two-point streamwise velocity correlations were used to investigate the large-scale coherent structures. The results revealed enhanced streamwise stretching of the structures as the offset height ratio decreased. In the combined region, the structures are more inclined towards the free surface as the offset height ratio decreased.
Development of a Measurement Method for the Classification and Performance Evaluation of Positive Pressure Ventilation (PPV) Fans
Authors: Fritsche Manuel , Epple Philipp , Delgado Antonio
Published: October 2018

Positive Pressure Ventilation (PPV) fans are used by fire departments. The specified performance data differ depending on the manufacturer, as there is no international and commonly accepted standardized measuring method for evaluating the PPV fan performance.

In the present work a new measurement method for the classification and performance evaluation of PPV fans is proposed. These fundamental investigations are based on numerical simulations and experimental test studies. The simulations have been performed with the commercial CFD software ANSYS CFX and the test measurements have been carried out on a newly developed test rig. For the predesign of the measurement method, the flow behavior of a free jet with swirl has been investigated with CFD simulations. A special feature of the PPV fans is that the generated flow rate is not only due to the flow through the rotating impeller, but also a significant flow rate is generated outside the PPV fan due to the viscous shear stresses (principle of a viscous jet pump).

For the measurements a new test rig has been designed in order to measure the flow velocity of the PPV fan as it is in real firefighter’s fire combat situations. The new test rig design concept and the numerical and experimental results of these studies are presented in detail in this work.
Effects of Ambient Air Relative Humidity and Surface Temperature on Water Droplet Spreading Dynamics
Authors: Jadidi M. , Farzad M. A. , Trepanier J. Y. , Dolatabadi A.
Published: October 2018

Water droplet impact on horizontal glass, aluminum, and superhydrophobic surfaces is experimentally investigated using high speed imaging. Experiments are performed at three different relative humidities (i.e. 10, 20 and 30%) and three surface temperatures (i.e. 20, 2 and −2°C) to ascertain their effects on droplet spreading and recoil behaviors. In this study, the droplet Weber number, Reynolds number, and the ambient air temperature are fixed at 16.2, 1687, and 23°C, respectively. The high-speed images of impact, spreading and recoil of the droplets as well as the temporal variations of droplet spreads are prepared. Results show that the ratio of surface temperature to dew point temperature (which depends on the air temperature and relative humidity) has a significant influence on droplet spreading, recoil, and contact angle. When this ratio is less than one, condensation and frost formation become important. Decreasing the mentioned ratio (it can be done by decreasing the surface temperature or increasing the relative humidity) causes the droplet spreading factor for hydrophilic surfaces to increase significantly. For superhydrophobic surface, decreasing this ratio (within the mentioned range) does not influence the maximum spreading. However, the recoiling phase is slowed down and the droplet detachment time form the superhydrophobic surface is increased noticeably. In addition, the equilibrium contact angle decreases as the mentioned ratio decreases.
Assessment of RANS, LES, and Hybrid RANS/LES Models for the Prediction of Low-Pr Turbulent Flows
Authors: Bhushan S. , ElFajri O. , Jock W. D. , Walters D. K. , Lai J. K. , Hassan Y. A. , Jackson R. Brian , Obabko A. , Merzari E.
Published: October 2018

The predictive capability of RANS, hybrid RANS/LES and LES turbulence models for momentum and thermal energy transfer in wall bounded low-Pr turbulent flows is investigated. Plane channel flow simulations are performed for Reτ = 150 and 640 for Pr = 0.025 and 0.71 with and without buoyancy effects, including both forced and mixed force/natural convection conditions, using the open source spectral element flow solver Nek5000. The prediction of one-point velocity and temperature statistics from the simulations are compared against available DNS results. Results are analyzed to understand the effect of flow conditions on turbulent thermal transport, and assess the relative strengths and weaknesses of the different modeling methods.
Utilization of Churn Flow Coalescer for Improving Foam Breakup in Gas-Liquid Cylinderical Cyclone
Authors: Dabirian Ramin , Gavrielatos Ilias , Mohan Ram S. , Shoham Ovadia
Published: October 2018

Foaming can hinder gas-liquid separation, therefore, it is desirable to break the foam upstream of separation facilities. There are different methods to breakup foam, including chemical (utilizing defoaming agent), mechanical (such as cyclones), and thermal (by increasing temperature).

Foam stability and breakup are studied in a standalone Churn Flow Coalescer (CFC) and in a Churn Flow Coalescer/Gas-Liquid Cylindrical Cyclone© (CFC/GLCC©) system. The goal is to investigate the possible improvement of the foam breakup efficiency in the GLCC© by installing a CFC upstream of the GLCC©. Testing the standalone CFC, it was found that the CFC generates more, but less stable, foam that can be broken more easily.

Three different CFC’s are tested with diameters of 1″, 2″ and 3″. For the same inlet conditions, the 3″ CFC with tangential inlet was found to be the most efficient for generating less stable foam. The optimal operating conditions for this CFC are at low superficial gas velocities, namely, vsg(CFC) between 0.1 to 0.3 m/s. Higher flow rates generate smaller bubbles and more stable foam. From testing the CFC/GLCC© system, it is found that foam breakup in this system is more efficient than that of the standalone GLCC©, under the same flow conditions.

The operational envelope of the CFC is predicted based on the transition boundary to churn flow developed by Taitel et al. (1980), as a function of the CFC aspect ratio (LE/D). The analysis of transition boundary between slug and churn confirm that less stable foam occurs at the left of churn flow transition boundary.
Experimental Study of Flow Around a Rotating Sphere at a Moderate Reynolds Number
Authors: Li Zhuoyue , Gao Nan
Published: October 2018

Aerodynamic forces on a rotating golf ball were measured in a water tunnel for a Reynolds number of ReD = 8000 at a spinning ratio Vs/Uo (the surface velocity over the freestream velocity) between 0 and 6.0. The flow fields downstream of a spinning sphere were also measured using a time-resolved stereoscopic PIV system with field-of-views perpendicular to the incoming flow to capture the three velocity components.There appeared to be several critical spinning ratios at Vs/Uo ≈ 0.75, 2.0 and 3.0. Both lift and drag increased quickly for Vs/Uo ≲ 0.75; there was a sudden drop in lift at Vs/Uo ≈ 0.75; lift increased quickly while drag increased slowly for 1.0 ≲ Vs/Uo ≲ 2.0; both lift and drag plateaued for 2.0 ≲ Vs/Uo ≲ 3.0; lift increased while drag decreased for large spinning ratios 3.0 ≲ Vs/Uo ≲ 6.0. Flow measurements suggested the lift increase was associated with a downwash downstream of spinning ball. Down wash induced a pair of counter-rotating vortices that caused increases in drag, similar to the induced drag on a finite-span wing. Boundary layer transition occurred on retreating side at a large spinning ratio 3.0 ≲ Vs/Uo ≲ 6.0, the downward appeared to be weaker in this situation and drag increased thus became smaller again.
Numerical Analysis on Drag Reduction of High-Speed Train Using Rough Surface
Authors: Yin Bo , Yang Guowei
Published: October 2018

Rough surfaces of flying and swimming animals help to reduce the aerodynamic or hydrodynamic drag when they move in the environment. In this research, biomimetic rough surface is introduced for high-speed train to reduce the aerodynamic drag. CFD tool is used to numerically study how the aerodynamic drag is altered by applying the biomimetic structures to the high-speed train surface. Rough surface is distributed in three areas: pantograph, bogie and windshield areas to reduce the drag at train speed of V = 400km/h. Concave is employed on these areas and orthogonally distributed with diameter of 40mm and center-to-center distance from 60mm to 80mm. The drag force is slightly increased/decreased in the pantograph area, while in the bogie and windshield areas rough structures lead to drag reduction with same distribution configuration. For all cases, the amount of shear drag change is much less than the pressure drag change. The total drag reduction mainly comes from pressure change. Rough surface positively contributes to changing the surface flow and thus reducing the aerodynamic drag.
Calculation of the Maximal Flight Altitude of the Historical HW2 Rocket Using CFD
Authors: Steppert Michael , Epple Philipp , Steber Michael
Published: October 2018

The historical HW2 rocket was a liquid propulsion rocket, designed by the German rocket pioneer Johannes Winkler in 1932. With this rocket, Winkler tried to reach a much higher altitude than with his first model, the HW1, which was the first liquid propulsion rocket in Europe and reached an altitude of 60 meters. Because of technical problems, the HW2 exploded immediately after the launch on October 6th in 1932 [1] [2].

To estimate the performance of this historical liquid propulsion rocket its maximum flight altitude was computed with the use of CFD. The equation of the vertical flight trajectory was solved numerically, with the classical Runge-Kutta method. For the computation of the vertical trajectory standard atmospheric conditions were considered. To determine the thrust and the drag of the rocket, the Navier-Stokes equations were solved with the commercial CFD solver Star-CCM+ from Siemens PLM Software. The rocket hull and the rocket engine were first simulated independently for different Mach-numbers and atmospheric flight conditions. Finally the complete rocket with running rocket engine was also computed in atmospheric flight conditions. These results were compared with the standalone simulations of the rocket drag without the running rocket engine and with the simulation of the rocket engine alone. The results are shown and analyzed in detail in this work.
Implementation of the Ffowcs Williams-Hawkings Equation: Predicting the Far Field Noise From Airfoils While Using Boundary Layer Tripping Mechanisms
Authors: Bodling Andrew L. , Sharma Anupam
Published: October 2018

A study was done to investigate how boundary layer tripping mechanisms can affect the ability of a permeable surface FW-H solver to predict the far field noise emanating from an airfoil trailing edge. The far field noise in a baseline airfoil as well as the baseline airfoil fitted with fin let fences was analyzed. Two numerical boundary layer tripping mechanisms were implemented. The results illustrated the importance of choosing a permeable integration surface that is outside any high frequency waves emanating from the trip region. The results also illustrated the importance of choosing a boundary layer tripping mechanism that minimizes any extraneous noise so that an integration surface can be taken close to the airfoil.
A Numerical Study of Flow Boiling Heat Transfer of Nanoemulsion in Mini-Channel Heat Exchanger
Authors: Xu Jiajun , Acar Musa , Poudel Naresh , Rios Jaime , Tran Thanh N.
Published: October 2018

In this study, a numerical study has been performed on the two-phase heat transfer of a new nanostructured heat transfer fluid: Water-in-Polyalphaolefin (PAO) Nanoemulsion Fluid inside a mini-channel heat exchanger using ANSYS FLUENT. Nanoemulsion fluids are liquid suspensions of nanosized droplets, which are part of a broad class of colloidal dispersions. The nanoemulsion fluid can be formed spontaneously by self-assembly, in which these nanodroplets are in fact swollen micelles. To simplify the complexity of the numerical model, the nanoemulsion fluid was then treated as a homogenous fluid during single-phase and only the water vaporizes during the phase change. The volume of fraction (VOF) model with Pressure-Velocity coupling based Semi Implicit Method for Pressure Linked Equations (SIMPLE) iterative algorithm is employed to solve the continuity, momentum, energy equations in two dimensional domains. The thermophysical properties of the nanoemulsion fluid were measured and used for the current simulation. The results were verified using the experimental results and has shown good agreement. This study has demonstrated the feasibility of simplyig the simulation of flow boiling heat transfer of this new heat transfer fluid through treating it as a homogenous fluid during single-phase convective heat transfer and separating the vapor phase of the nano-micelles during flow boiling. This study has also shown that this Water-in-PAO nanoemulsion could function as a good and alternative conventional working fluid in heat transfer applications.
Gas Carry-Under in GLCC for Separated and Recombined Outlet Configurations
Authors: Kolla Srinivas Swaroop , Mohan Ram S. , Shoham Ovadia
Published: October 2018

Gas Carry-Under (GCU) is one of the undesirable phenomena that exists in the GLCC©1 even within the Operational Envelope (OPEN) for liquid carry-over. Few studies that are available on GLCC© GCU have been carried out when the GLCC© is operated in a metering loop configuration characterized by recombined outlets. In such configurations the gas and the liquid outlets of the GLCC are recombined downstream which acts as passive level control. However, studies have shown that the GLCC© OPEN increases significantly when active control strategies are employed. There has not been a systematic study aimed at analyzing the effect of control on the GCU in the GLCC. This study compares the previously published GLCC GCU swirling flow mechanism under recombination outlet configuration with data taken under the separated outlet configuration (control configuration). Experimental investigations for GCU are conducted in a state-of-the-art test facility for air-water and air-oil flow incorporating pressure and level control configurations. The experiments are carried out using a 3″ diameter GLCC© equipped with 3 sequential trap sections to measure simultaneously the Gas Volume Fraction (GVF) and gas evolution in the lower part of the GLCC. Also, gas trap sections are installed in the liquid leg of the GLCC© to measure simultaneously the overall GCU. The liquid level was controlled at 6″ below the GLCC© inlet for all experiments using various control strategies. Tangential wall jet impingement is the cause for entrainment of gas, thereby leading to GCU. 3 different flow mechanisms have been identified in the lower part of the GLCC and have significant effect on the GCU. Viscosity and surface tension are observed to affect the GCU. The extensive acquired data shed light on the complex flow behavior in the lower part of the GLCC© and its effect on the GCU of the GLCC©.
Numerical Investigation of the Flow in Hydrostatic Journal Bearings With Porous Material
Authors: Böhle M.
Published: October 2018

The numerical prediction of load capacity, stiffness, power loss etc. of hydrostatic journal bearings must be performed for technical applications. CFD offers one possibility but is time consuming. In the present contribution a fast working numerical method is introduced based on the numerical solution of the Reynolds equation for hydrodynamic lubrication (REHL). It is applied in order to examine the flow inside three-dimensional journal bearings. The emphasis lies on the treatment of journal bearings with porous material. By the application of porous material the lubricant can be fed uniformly around the shaft and therefore improves the reliability of the journal bearing. The contribution gives a short outline of the possibilities and limitations of the application of the REHL. A detailed description of a finite difference method is given by which the REHL is solved. It is described in detail how the load capacity, stiffness, volume flow rate etc. of classical hydrodynamic journal bearings and journal bearings with porous material can be treated by the REHL whereby the emphasis lies on the treatment of journal bearings with porous material. Darcy’s law is implemented in the numerical method in order to take into account the pressure loss of the porous material which is the flow restrictor of the journal bearing. Many results are shown and discussed. Pressure distributions, load capacity, volume flow rates through the porous material, direction of force for a hydrodynamic and porous bearing etc. are shown and discussed in dependence of the eccentricity of the shaft.
Threshold Criteria for Components of Predictive Model for Pipe Flow of Broadly-Graded Slurry
Authors: Matoušek Václav , Visintainer Robert , Furlan John , Sellgren Anders
Published: October 2018

Industrial slurries transported in pressurized pipelines often consist of particles of broad size distribution. The broad particle size distribution affects slurry flow behavior in a pipe. A four-component model (4CM) predicts the frictional pressure drop in pipe flow of broadly graded slurry. The model considers Newtonian carrying liquid and splits the broadly graded solids into fractions (components) each of which contributes to the pressure drop through its own dominating friction mechanism expressed by a particular sub-model in the 4CM. The sorting of the solids into the components (carrier, pseudo-homogeneous, heterogeneous, fully-stratified) must be based on appropriate criteria. For the sake of simplicity, the 4CM currently uses threshold sizes of particles to split the solids into 4 components.

The goal of the present work is to analyze the existing criteria for the threshold between the pseudo-homogeneous component and heterogeneous component and for the threshold between the heterogeneous component and fully-stratified component. The analysis is based on a description of mechanisms governing particle support (suspension, deposition) of each particular solids component in slurry flow. It shows that the existing grain-size thresholds actually express certain proportions among threshold velocities of flow delimiting different slurry flow regimes. Such threshold velocities are the deposition-limit velocity, the initial-suspension velocity, and the full-suspension velocity. We discuss the proportions and demonstrate how properties (of liquid, solids, flow) and associated parameters additional to the grain size may influence the thresholds.

The analytical results are supported by experimental results for flow of individual components in a laboratory loop.
Study of Flow Field of a Residential Gas Furnace With Particle Image Velocimetry
Authors: Wu Puyuan , Shang Weixiao , Chen Jun
Published: October 2018

Nearly 45% of the residential site energy in the US is consumed by the gas furnace for space heating. The design practice of next-generation product often refers to CFD-based design tool, in order to reduce the development cost and cycle. In the present study, Particle Image Velocimetry (PIV) is applied to measure the detailed flow field inside a general gas furnace model for establishing a benchmark database and validating CFD predictions. The furnace model is equipped with multiple observation windows and is connected to an air circulation system with seeding particles introduced, simulating different well-controlled operation conditions. The flow field around the four primary heat exchangers and at the outlet of the furnace is measured and analyzed statistically. The mean velocity displays symmetric patterns as the differential pressure between inlet and outlet of the furnace is low. The symmetry is transiently lost as the differential pressure increases. Statistical analysis also shows turbulence in regions with flow separation and vortex shedding. The results provide a clear understanding of the change of flow characteristics under different operation conditions.
Second Stage Optimization of Helical Groove Seals Using Computational Fluid Dynamics to Evaluate the Dependency of Optimized Design on Preswirl
Authors: Watson Cori , Wood Houston
Published: October 2018

Helical groove seals are non-contacting annular seals used in pumping machinery to increase the efficiency and, in the case of the balance drum, to manage the axial force on the thrust bearing. Prior work has shown that optimization of helical groove seals can reduce the leakage by two thirds given a desired pressure differential or, conversely, can significantly increase the pressure differential across the helical groove seal given a flow rate. This study evaluates the dependency of the optimal helical groove seal design on the inlet preswirl, which is the ratio of the inlet circumferential velocity to the rotor surface speed. To accomplish this goal, second stage optimization from the previously optimized helical groove seal with grooves on the stator and water as the working fluid were conducted at a series of preswirls ranging from −1 to 1. Optimization is performed using ANSYS CFX, a commercial computational fluid dynamics software and mesh independence is confirmed for the baseline case. For each preswirl case, design of experiments for the design parameters of groove width, groove depth, groove spacing, and number of grooves was performed using a Kennard-Stone Algorithm. The optimized solution is interpolated from the simulations run by using multi-factor quadratic regression from the 30 simulations in each optimization and the interpolated solution is simulated for comparison. In addition to evaluating the optimized solution’s dependency on preswirl, the viability of using swirl breaks or swirl promoting inlet passages to improve the overall efficiency of the seal is discussed. Finally, the power loss performance is evaluated for each of the seal designs simulated so that potential trade-offs can be evaluated. Overall, the results show that increasing preswirl can increase the efficiency of the helical groove seal both by improving power loss and by improving leakage.
An Experimental Study of Surface-Mounted Bluff Bodies Immersed in Deep Turbulent Boundary Layers
Authors: Amorin Helen A. , Fang Xingjun , Tachie Mark F.
Published: October 2018

This paper reports an experimental study conducted to investigate the effects of aspect ratio on the reattachment length and statistical properties in turbulent flow over three-dimensional surface-mounted bluff bodies. This study focuses on a surface-mounted body whose height is significantly smaller than the thickness of the approaching turbulent boundary layer. The studied aspect ratios of the step range from w/h = 0.5 to 20, where w and h denote the spanwise width and height of the step, respectively. All experiments were carried out in an open water channel, and the velocity measurements were performed using a time-resolved particle image velocimetry (TR-PIV) system. The Reynolds number, based on the freestream of the approach boundary layer and step height, is 12540, while the ratio of the boundary layer to step height is 4.83. Two distinct regions of separation are observed on top of the step and downstream of the step. In both separation regions, the reattachment length increases monotonically as aspect ratio increases from w/h = 0.5 to 8, and the reattachment length reaches an asymptotic value and does not vary significantly with aspect ratio larger than 8. The effects of aspect ratios on the mean velocities and Reynolds stresses were also examined.
Construction of a Rain Erosion Test Rig for Wind Energy Blade Coatings
Authors: Mühlbauer Moritz , Thamsen Paul U. , Liersch Jan , Michael Julian , Wagner Maik
Published: October 2018

Wind turbine blades are constantly exposed to weather conditions, which wear and degrade the surface [1]. Depending on the site of the plant, rain is the main driver for this wear. This rain erosion becomes apparent, when the coating — usually on the leading edge — shows a rough surface or even the bare GFRP looms.

Increased surface roughness usually goes along with diminished performance. This surface erosion occurs mostly near the tips of the blades, where most power is converted. Maintenance teams replace the damaged coatings in costly rope-based operations. To extend maintenance intervals and select the best coating, better understanding of the loads and the non-linear development of erosion damage is necessary.

Therefore a test rig to simulate realistic erosion loads is constructed. The velocity between the surface and the droplet is created by a rotating arm with a vertical axis and a stationary nozzle in one side, similar to the rotating arm apparatus in [2], but much smaller. Our approach is to use relative velocities between droplets and coating which are comparable to the ones seen on wind turbines, as well as a realistic droplet size distribution [3] and ambient pressure.

Rotational speed, temperature, vibrations, flow rate, electric voltage and current are constantly measured to ensure safe operation and repeatable measurements.
Fourier-Bessel Series Model for the Stefan Problem With Internal Heat Generation in Cylindrical Coordinates
Authors: Barannyk Lyudmyla , Crepeau John , Paulus Patrick , Siahpush Ali
Published: October 2018

A nonlinear, first-order ordinary differential equation that involves Fourier-Bessel series terms has been derived to model the time-dependent motion of the solid-liquid interface during melting and solidification of a material with constant internal heat generation in cylindrical coordinates. The model is valid for all Stefan numbers. One of the primary applications of this problem is for a nuclear fuel rod during meltdown. The numerical solutions to this differential equation are compared to the solutions of a previously derived model that was based on the quasi-steady approximation, which is valid only for Stefan numbers less than one. The model presented in this paper contains exponentially decaying terms in the form of Fourier-Bessel series for the temperature gradients in both the solid and liquid phases. The agreement between the two models is excellent in the low Stefan number regime. For higher Stefan numbers, where the quasi-steady model is not accurate, the new model differs from the approximate model since it incorporates the time-dependent terms for small times, and as the system approaches steady-state, the curves converge. At higher Stefan numbers, the system approaches steady-state faster than for lower Stefan numbers. During the transient process for both melting and solidification, the temperature profiles become parabolic.
Filtration Technology Research of Graphite Dust Produced in Spent Fuel Transportation Process in HTR-PM
Authors: Wang Jinhua , Wang Bing , Wu Bin , Li Yue , Wang Haitao
Published: October 2018

With the continuous development of the nuclear power technology in the world, all countries in the world are becoming more and more interested in the inherent safety of nuclear power technology, while the research and development of the spherical bed type high temperature gas cooled reactor nuclear power technology in China has formally catered to this demand.

As a major national science and technology project, since the construction of the high temperature gas cooled reactor demonstration project (HTR-PM) since 2012, the civil construction of the nuclear island has been basically completed, the installation of equipment has been carried out orderly, and many process systems have entered debugging and operation stage gradually.

As an important auxiliary process system, fuel handling and storage system for online refueling of the pebble bed high temperature gas cooled reactor, plays an important role in relation to the stable operation of the reactor.

The main functions of the fuel handling and storage system are loading the fresh fuel elements and unloading the spent fuel elements which has reached its target burnup continuously for reactor operation, the spent fuel elements would be discharged into the spent fuel canister firstly, when the spent fuel storage canister is full of spent fuel, the canister would be sealed through welding method, and then the spent fuel canister would be transferred and stored in the spent fuel storage silo with the ground crane system.

The fuel element of the pebble bed high temperature gas cooled reactor is spherical fuel element with graphite matrix, the fuel elements will have friction and collision with the inner wall of the pipeline in transporting process, which will produce graphite dust, the graphite dust should be removed continuously though filtration method, so as not to affect the fuel elements transportation in pipeline.

This article focus on the production mechanism and filtering method of the graphite dust in graphite matrix fuel element transporting process in pipeline, to study the graphite dust removal technology, and then we could provide theoretical guidance for the design and operation of the key system and equipment for HTR-PM.
Numerical Simulation for Nuclear Engineering Education: A Case Study in a Course “Advanced Nuclear Reactor Thermal Analysis”
Authors: Huang Shanfang , Gong Yaopeng , Li Chao , Liu Ruilong , Wang Jiageng , Wang Kan
Published: October 2018

Nuclear energy is an important way to solve energy shortage and pollution problems today. Therefore, China is vigorously developing nuclear energy and is facing huge demands for talents. However, nuclear engineering education has been severely hampered, particularly in its experiment aspect because of the Fukushima accident. The original sub-critical nuclear reactor at Tsinghua University (THU) was stopped, forcing students to use computers to conduct relevant nuclear simulation experiments.

The emerging of supercomputers and commercial numerical simulation softwares has provided enough hardware and software support for complex calculations required in numerical simulation of nuclear reactors. Thus numerical simulation could be integrated into nuclear engineering education. With its ease of use, quick acquisition and direct visualization of results, numerical simulation can save much time and money. Besides, it is convenient to change simulation conditions which is helpful for academic research and talent development.

This paper starts with THU’s nuclear engineering talent training mode, and taking the course “Advanced Nuclear Reactor Thermal Analysis” as an example, discusses the applications of numerical simulation softwares FLUENT and COBRA-TF in this course. Finally, the analysis shows that numerical simulation performs well in conceptual understanding and experimental design. It plays a significant role in nuclear engineering education, which provides an important reference for the new mode of nuclear engineering education.
Experimental Study of Radon Exhalation Rate in Uranium-Like Rock Based on Closed Chamber Method
Authors: Jiang Fuliang , Wang Xiaoli , Zhang Shuai , Li Xiangyang , Hong Changshou
Published: October 2018

The closed chamber method is widely used in measuring radon exhalation rate, which can avoid the error caused by the leakage and anti-diffusion phenomena. Firstly, considering the actual situation that uranium ore is difficult to obtain and have a high radioactivity, the uranium-like rock was made according to the similarity theory. Secondly, the diffusion length and intrinsic radon exhalation rate were obtained by using the closed chamber method. Thirdly, the theoretical values of radon exhalation rate made by uranium-like ore block were calculated, compared with the measured values. This study shows that the uranium-like rock block made by the best mass ratio is helpful for the subsequent experiment, and the error between the theoretical calculation and the measured value is no more than 9.14%. This indicates it is reliable to estimate radon exhalation rate by diffusion length and intrinsic radon exhalation rate and can also provide a foundation for rapidly gaining radon exhalation rate of the same type material by the closed chamber method. This study can further promote the study of the radon exhalation rate under the complex physical conditions and then better guide the protection work of radon radiation in underground mining.
Experimental Investigation on Critical Heat Flux in Horizontal Tube
Authors: Chuanxin Peng , Yuanfeng Zan
Published: October 2018

The critical heat flux (CHF) in horizontal tube under low flow condition is investigated in this paper. It is found that the boiling crisis occurs at the upper surface of the horizontal tube. According to the exit quality and flow pattern, the category of boiling crisis in the horizontal tube under low flow is considered to be Dryout. The prediction results of Bowring correlation and Lookup table are much larger than the experimental data. Because the Bowring correlation and Lookup table are proposed for the CHF prediction of vertical round tube. The distribution of liquid film in horizontal annular flow is asymmetrical due to gravity. The non-uniform distribution of the liquid film reduces the CHF.
Derivation of Critical Parameters of Betavoltaics
Authors: Cheu Darrell S. , Adams Thomas E. , Revankar Shripad T.
Published: October 2018

Betavoltaic cells are nuclear batteries ideal for low-power applications for extended periods of time without maintenance or replacement. Betavoltaics function similarly to photovoltaic (solar) cells where instead of using sunlight, beta particles are used to generate electron-hole pairs within a semiconductor p-n junction to generate current. Even though there have been multiple demonstrations, betavoltaic performance has not been extensively studied. To accurately predict betavoltaic performance, which is important for a device in operation without maintenance for elongated periods, all parameters are required to predict potential fluctuations in cell performance, such as doping densities and resistances for semiconductor variation and absorption coefficients for beta-generated current. However, not all parameters are easily measured, especially when the p-n junction is constantly under irradiation and cannot be separated from the source. Critical parameters were characterized experimentally with the betavoltaic cell by performing capacitance-voltage to determine doping densities and performing current-voltage characterization tests to determine resistances on multiple NanoTritium™ cells, while absorption coefficients were determined from MCNP6 simulations. Experiments indicated that series resistance Rs was 1 × 106 Ω, while shunt resistance Rsh was 2 × 108 Ω from I-V characterization, while doping density ND was determined to be 1 × 1017 cm−3 from C-V characterization. Absorption coefficient α was found to vary with semiconductor material and incoming beta energy and used in conjunction with critical parameters from experimentation to accurately model betavoltaic cell performance similar to experimental results. Both implicit equations and explicit estimations were compared to model betavoltaic cell performance.