bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling of Free Surface Flow Within the Two-Fluid Euler-Euler Framework
Authors: Porombka Paul 
Published: July 2018

Two-phase flows are regularly involved in the heat and mass transfer of industrial processes. To ensure the safety and efficiency of such processes, accurate predictions of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) are required. Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of the turbulent shear stress and the interphase momentum transfer.
As a long term objective, the research activities at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) pursue the development of general models for two-phase flows which are based on first principles and include less empiricism. Part of this effort is focused on the development of an algebraic interfacial area density model (AIAD) which enables the simulation of two-phase flows with general morphologies including bubble, droplet and stratified flow regimes with the two-fluid approach. In this work a short overview of the AIAD model is given and recent developments are presented.
The modelling of the interfacial drag in free surface flows is of particular interest and subject to ongoing research. Apart from empirical correlations, which are limited to certain flow regimes, different models for the local calculation of the interfacial drag have been developed. The latter approach is followed in the AIAD model and has recently been subject to modifications which are presented and validated as a part of this study.
Furthermore, special attention is paid to the turbulence treatment at the phase boundary of free surface flows. A general damping of the gas-side turbulent fluctuations in the near interface region has been described previously in the literature but has not yet found its way into eddy viscosity turbulence models. In this work, a previously proposed damping source term for the k-ω turbulence model is validated.
Model validation is performed by comparing the simulation results to experimental data in case of stratified, countercurrent air-water flow in a closed channel.
Effects of Diffuser Length on Cloud Cavitation in an Axisymmetrical Convergent-Divergent Nozzle
Authors: Sato Keiichi , Takahashi Naoya , Sugimoto Yasuhiro 
Published: July 2018

Unsteady behavior of periodic cloud cavitation is typically observed in the field of fluid machinery under a high speed liquid flow such as a cavitating hydrofoil as well as cavitating water jet. The instability of cloud cavitation remains to be completely solved though it has been confirmed that there are two instabilities which is an intrinsic instability of cavitation and a system instability. Sato, et al. have found through previous investigations that the pressure wave at the collapse of shedding clouds can make a trigger to cause a reentrant motion.
In the present study, the authors focus on a cavitating water jet to investigate the cavitation aspects in an axisymmetrical convergent-divergent nozzle and examine an unsteady behavior of cloud cavitation through high speed video observation and image analysis based on the frame difference method. Especially, the authors study the effect of nozzle divergent part (diffuser) as well as the upstream pressure effect on cloud cavitation in the nozzle. As a result the authors have found that there are two kinds in the shedding pattern and the reentrant motion pattern for cloud cavitation depending on the nozzle diffuser length.
Hydraulic Design and Performance Adjustment of a Reverse Running Pump Turbine Based on a Double Suction Pump
Authors: Kagawa Shusaku , Sakurai Takaki , Kaneko Hiroyuki , Okamoto Hidenobu 
Published: July 2018

This paper described a reverse running double suction centrifugal pump turbine, which was newly designed and developed in order to adopt at a high fixed rotational speed 2980 [min−1] with high head H=245.6 [m]. New turbine model was developed by using CFD and its performance was validated by model test. There were a few studies about a reverse running pump turbine. However, a method of “Q-H performance adjustment” for the pump turbine is not clear. In order to reveal a method of Q-H performance adjustment of a turbine, CFD simulation and model test was carried out.
The model test results showed that the performance of new turbine model fully satisfied Q-H requirement. And the results of steady CFD simulation were in good agreements with the model test results.
Two possible methods to adjust the Q-H performance curve of a reverse running double suction centrifugal pump turbine were confirmed by model tests and CFD. The first method was modifying a throat sectional area of inlet spiral casing by cutting off a casing tongue. The model test result showed that this method moves the Q-H performance curve of turbine from high head to lower head at a constant capacity with very small efficiency drop at rated operating point. The result of CFD showed that, the Q-H performance change was obtained by the change in absolute tangential velocity at the runner inlet, which represents the inlet angular momentum, by the modification of throat sectional area.
The second method was adjusting the runner outlet velocity triangle by modifying the runner blade trailing edge profile by under-filing or over-filing. The model test result proved that, the above modification of runner blade trailing edge profile is effective to control the Q-H performance curve of a reverse running pump turbine.
The Research of Thermal Characteristics of Mechanical Seal Under High Temperature and High Viscosity Medium
Authors: Huilong Chen , Qiang Zou , Jie Fu , Jinfeng Liu , Shulin Li 
Published: July 2018

The purpose of this study is to study the thermal characteristics of mechanical seal under high temperature and high viscosity media, to provide a basis for the thermal deformation studies of the sealing ring and the effective control of flushing fluid. The mechanical seal ring (AR201 type) was taken as the research object, the combined effect of frictional heat, shear heat, flushing fluid was considered to establish of heat transfer calculation model. The finite element method was used to analysis temperature field with variable speed, different temperature and pressure of flushing fluid, the results show that the maximum temperature was nearby the center of the contact surface of the rotational ring and stational ring, which increases sharply with the speed increasing. The temperature gradient of stationary ring face ranges greater than that of the rotational ring.
The average temperature of axial section decreases along the axis, which of stational ring reduces faster than the rotational ring. The temperature of end surface increases with the increasing temperature and pressure of flushing fluid. To ensure the flushing effect of the sealing ring and operation steadily, fluid temperature was preference between 14 ° C ∼ 18 ° C, pressure of 0.8MPa ∼ 0.9MPa.
Effect of Inner Shape on Thermo-Fluid Characteristics of an Electric Vehicle Motor
Authors: Yuasa Tomohisa , Hirano Satoru , Kanagawa Tetsuya , Kaneko Akiko , Abe Yutaka 
Published: July 2018

Toward the improvement of performance of the electric vehicle (EV), the design of the motor shape appropriate to a good heat removal is important. A typical EV motor is composed of a pair of coaxial cylinders with the fixed outer cylinder (stator) and the rotating inner cylinder (rotor). The gap of the coaxial cylinders is extremely narrow, i.e. 1 mm. In addition, the EV motor may have axial slits on the stator wall is considered. Thus, thermo-fluid characteristics of rotating coaxial cylinders with these features are important for the viewpoint of optimal design of the EV motor.
The aim of the present study is to clarify thermo-fluid characteristics in the narrow gap between a pair of coaxial cylinders simulating an EV motor at a high Reynolds number. The flow behavior in slits between the rotor and stator was measured by PIV with fluorescent particles distributed in the water, and was numerically examined.
Experimental apparatus simulating the EV motor was made of acrylic, and flow inside the EV motor was visualized by tracer particles. Using a high-speed video camera and Nd:YAG laser, flow in slits was observed. Visualization results show Taylor-Couette flow in the gap between the rotor and stator. Moreover, pathlines in the slit was observed, where a vortex was observed in the slit.
In the numerical calculation, two cases were executed to elucidate the slit effect: Case A is the stator without slits and Case B is the stator with slits. As a result, heat flux of Case B in the high rotational speed was increased compared with that of Case A. Hence, it was implied that the heat flux was increased by the presence of vortex of the internal slits.
Mixing of Matter by a Falling Spherical Particle in a Still Liquid
Authors: Koso Toru 
Published: July 2018

The mixing of liquid mass caused by a spherical solid particle falling in a still liquid in a pipe was investigated by visualization and noninvasive concentration measurement using a photochromic dye. A spherical particle with diameter of 4.76 mm was dropped in a kerosene-paraffin mixture liquid with a photochromic dye. The photochromic dye was activated by an ultraviolet light and was subjected to the mixing by the particle wake. The falling velocity of particle was changed by using 8 different densities of particle. The effect of the particle Reynolds number on the mixing was investigated for the Reynolds number range from 10 to 2490. The effect of liquid viscosity on the mixing time was also investigated using two liquids having different viscosity.
The visualized dye patterns indicated the mixing process depended strongly on the particle Reynolds number. For the Reynolds numbers higher than 300, the particle shed the vortices behind the particle and the dye was mixed isotropically by large-scale vortices. For the Reynolds numbers lower than 300, the dye was drawn straightly by a laminar wake of the particle.
The concentration of the mixed dye was measured using the photochromic concentration measuring (PCM) technique to discuss the mass mixing quantitatively. The turbulent diffusion coefficient (TDC) was evaluated for the cases the dye was mixed by the vortices. It was found that the evaluated TDCs showed strong time-dependency, which was attributed to the change in scale and whirling velocity of wake vortices. The maximum TDC depended on the falling velocity regardless of the fluid viscosity. The mixing time depended strongly on the liquid viscosity. The mixing time of the TDC was suggested to be governed by the viscous decay time and expanding time of vortices in the pipe.
The amount of dye drift was evaluated for the cases the particle wake was laminar. It was found that the dye drift increased sharply just after the particle passing and then saturated. The final dye drift increased gradually with increasing Reynolds number.
Study of the Flow Field and Performances of a Centrifugal Pump During Unstable Operating Conditions by CFD
Authors: Prunières Romain , Imai Neo , Inoue Yasuhiro , Okihara Takashi , Nagahara Takahide 
Published: July 2018

Centrifugal pumps curve instability, characterized by a local dent and uprising head curve, often causes severe problems such as vibrations and noises. At low flow rates, stability of performance curve is necessary for reliable operation of the pump. Most of the studies regarding centrifugal pumps curves instability focus on flow rate around 60 % of the best efficiency flow rate. The purpose of present investigation is to analyse the causes of the occurrence of performance curve instability by means of Computational Fluid Dynamics (CFD) and to understand the mechanism of such instability at flow rates around 30 % of best efficiency flow rate.
In order to understand the causes of the performance curve instability, two impellers with different outlet shape are analysed. During experimental tests, performance curve instability appeared around 30 % of the best efficiency flow rate on the first impeller while the second impeller remains stable. CFD analysis also shows unstable performance curve for the first impeller, and stable for the second one. Hence, a detailed analysis of the flow field of the two impellers and a quantitative comparison are performed in order to characterize the instability phenomenon.
Unsteady Flow due to Cavitation in Mixed Flow Pumps Second Report: The Effect of Tip Vortex Cavitation on Hydraulic Force
Authors: Nakano Takuya , Hano Yohei , Masuda Naoki , Maeda Hideaki 
Published: July 2018

Large vertical mixed flow pump is often used as the sea water supply pump in MSF (Multi-stage Flash) seawater desalination plant. From the point of view of cost reduction, the smaller pump size is strongly required for this type of pump. To satisfy this requirement, higher suction performance should be achieved but there are several issues such as excessive noise, vibration and erosion caused by cavitation in high velocity flow field [1]. Therefore, the present work is aimed at establishing the design technique for suppressing the cavitation which occurs in high velocity field in mixed flow pump.
As reported in the previous paper [2], we experienced irregular excessive vibration due to cavitation in vertical mixed flow pump. Although this issue had been solved by applying forward swept impeller [3], the relation between the vibration and tip vortex cavitation was still unclear.
This paper describes the investigation results about the relation between unsteady hydraulic exciting force and tip leakage vortex cavitation by CFD (Computational Fluid Dynamics). In the CFD analysis, the tip clearance was considered and full cavitation model was used to evaluate the effect of tip vortex cavitation on hydraulic exciting force [4].
From the CFD analysis, the vortex core induced from leading edge of impeller blade was detected and the static pressure and vorticity distributions on vortex center were obtained. From these results, there was no significant difference of these values between no-swept and forward swept impellers. Therefore, it implies that sweep technology does not affect to the strength of vortex. On the other hand, the unsteady behavior of pressure and cavitation area on the impeller blade was observed. Accordingly it is supposed that this fluctuation induced excessive noise, vibration and erosion.
A Tilting Pad Journal Bearing Model for Coupled Fluid Dynamical-Rotor Dynamical Analyses
Authors: Conti R. , Frilli A. , Galardi E. , Meli E. , Nocciolini D. , Pugi L. , Rindi A. , Rossin Stefano 
Published: July 2018

Turbomachines are continuously developing in order to reach higher levels of speed, power and efficiency and the classical Fixed Geometry Journal Bearings have been replaced by Tilting Pad Journal Bearings to avoid instability phenomena. In this paper, the authors propose an innovative quasi-3D TPJB modelling approach that allows the simultaneous and coupled analysis of the typical phenomena involved in TPJB operations. The authors focused on the accurate analysis of the interactions between the rotor and the lubricant supply plant and on the fluid dynamical effects due to the bearing that cause those couplings, aiming at reaching a good compromise between the accuracy and the numerical efficiency of the model (mandatory to analyze systems with many bearings).
The TPJB model has been developed and experimentally validated in collaboration with Nuovo Pignone General Electric S.p.a. which provided the technical data of the system and the results of experimental tests.
Experimental Assessment of Joint-Like Modal Models for Structures
Authors: Segalman Daniel J. , Allen Matthew S. , Eriten Melih , Hoppman Kurt 
Published: July 2018

Several of the authors, and others, have explored the use of modal-like models for structures having nonlinearities associated with compressive joints (such as bolted connections.) In these models, the deformations are treated as consisting of modal expansions, but with the modal coordinates that evolving nonlinearly over time. There have been several theoretical treatments of this strategy and the authors report here on an early effort to confirm the approach through experiment.
For this purpose simple structures consisting of pairs of plates were assembled using four bolted connections. The structures were excited by modal hammer at various locations and the modes identified by scanning laser vibrometer. In each case, multiple modes were excited and the evolution of modal coordinates was achieved by band-pass filtering at the relevant frequencies.
Making some simple kinematic assumptions about relative deformations of the component plates and exploiting symmetries permits the mapping from ring-down of each mode to constitutive behavior of each joint. If the strategy of using joint-like modal models for bolted structures is valid, the joint constitutive models deduced from any mode should be adequate to predict the apparent, but nonlinear modal behavior at other resonances. Multiple test specimens were manufactured to assess this predictive capability in the context of part-to-part variability intrinsic to the dynamics of such structures.
A Semi-Stented and Chorded Mitral Valve Prosthesis: Design and Method of Chordal Setting and In Vitro Testing
Authors: Kotzé R. , Deorsola L. 
Published: July 2018

Mitral subvalvular apparatus plays an important role in mitral and ventricular dynamics by preserving annuloventricular continuity, known to be fundamental for ventricular function. While some proposed mitral valve prostheses designs do attempt to account for this relationship by using papillary flaps, they are not adjustable and do not mimic the native saddle shaped mitral annulus. Unfortunately, these designs are not versatile as their papillary flap lengths cannot be altered and the prostheses are unsuitable for percutaneous implantation.
We address these issues through the design of a novel semistented and chorded mitral valve that better mimics the native mitral annulus, leaflets and chordae function and can be made from off-the-shelf biomaterials with the potential to be implanted percutaneously. We also propose a novel and reliable method to set the chordal lengths individually. Finally, we demonstrate the hydrodynamic performance of the valve, showing that it meets the minimum performance requirements stipulated by the international standard ISO 5840-3:2013.
Performance Evaluation of Gear Pump by 2D Unsteady CFD Analysis
Authors: Kumar K. Anil , Balamuralikrishnan N. 
Published: July 2018

Gas Turbine development activities have been associated with development of different pumps and its allied subsystems used for fuel supply and lubrication oil supply at different engine operating condition.
2D transient flow analysis of a Dual pump has been carried out in an environment with an adverse pressure gradient to map important parameters like pressure, velocity, mass flow and effect of slip. Three achievable close tolerances were selected and carried out the analysis. Finally identified tolerance to be maintained during manufacturing based on the analysis.
A moving dynamic mesh concept was adopted because of its capability to facilitate solving transient flow problem and motion of the domain boundaries. A simulated motion control was decided based on the time step, angular velocities of gears rotation motion and coded through a User defined function (UDF) to give angular momentum. Each analysis was carried out for 180 degree of rotation. The main parameter mass flow rate was monitored for different speed and outlet pressures. A validation experimental test was carried out at one rpm thus build up a confidence in implant design synthesis to meet challenges in future.
Design and Analysis Software for Propellers
Authors: Prathapanayaka Rajeevalochanam , Vinod Kumar Nanjundaiah , Settisara Janney Krishnamurthy , Nagishetty Hari Krishna 
Published: July 2018

Recent interest in the field of micro and nano scale air vehicles attracted the attention of many researchers all over the world. The challenge associated with these classes of vehicles is to develop efficient miniaturized components. There are different types of micro and nano air vehicles out of which fixed wing micro air vehicle is one of them. Propulsion system for most of the fixed wing MAVs is propeller driven by an electric motor powered by a battery. The endurance of the MAV mainly depends on the performance of these two components. Hence there is a scope to improve the performance of the propeller and motor. Efficient propeller design and its performance analysis are an iterative process and time consuming. In the present study, to ease the process of propeller design and analysis NALPROPELLER code has been developed using MATLAB. This code is based on minimum induced loss theory presented by E.E.Larrabee to generate planform, blade element momentum theory along with Prandtl hub-tip loss model for overall performance analysis and the performance plots could be viewed in the GUI windows. The code consists of three modules namely single airfoil design, multi airfoil design and analysis module. This code is compared with one of the propeller design and analysis code available in the internet JavaProp by Martin Hepperle, which is also based on minimum induced loss method.
From literature Eppler 193 airfoil show high lift to drag ratios at low Reynolds numbers [16]. Eppler-193 airfoil is used in the evaluation of propeller performance.
A four inch diameter, two bladed, fixed pitch propeller is designed and analysed using this code. The design is compared with one of the design software JavaProp available online as an open source. A poly urethane casting propeller is fabricated based on the design. The performance comparison of the NALPROPELLER code, JavaProp and 3D CFD analysis is presented and discussed.
Aeroderivative Gas Turbine Coupling Generator Redesign
Authors: Hernández Rossette Alejandro , García Illescas Rafael , Mazur Zdzislaw 
Published: July 2018

A major failure event was experienced at a 44 MW plant powered by four aeroderivative gas turbines arranged in two units, property of the Federal Commission of Electricity (CFE).
The failure consisted of total fracture in the shaft coupling between the generator and free-turbine. Unit 2 has a twin pack configuration with two aero derivative Pratt&Whitney 20 MW gas turbines coupled to one generator at both end sides. The “A” side generator coupling was completely damaged as well as the coupling configuration at the free turbine.
Failure analysis showed as root cause, an abnormal configuration of the coupling systems between the free turbine to rotor generator at side “A”. This side had an additional shaft component to compensate a longer coupling distance between the turbine and generator. This was longer than the original distance, generating additional dynamic forces during operation leading to a fatigue failure mechanism.
The replacement coupling configuration for the rotor generator was different than the Original Equipment Manufacturer (OEM). The new (non-OEM) spare rotor generator was shorter in the longitudinal direction than the original one, forcing the addition of a new shaft in one side of the generator.
This work describes the rehabilitation process of the generator coupling by the replacement of the old configuration by a new redesigned coupling. This was done keeping the original configuration distances and components for both end shaft sides of the rotor generator. The paper includes the redesigned couple analysis by finite element method and the in-situ activities for the installation of the new couple in the rotor generator.