bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of a Singularity- and an Inverse Design Method for Axial Flow Fans Based on Numerical Simulations
Authors: Theis Anika , Böhle Martin
Published: November 2019

In this contribution two different design methods for axial flow profiles are presented. A direct method based on a singularity method (SDM) is compared with an inverse design method (IDM). For the application of the SDM a profile is used with a circular arc camber line and a thickness distribution of bisuper-ellipses. The stagger angle is adjusted in such a way that the turning of the flow on the cross section is realized. For the adjustment of the stagger angle of the cross section the fast working SDM is applied. The stagger angle is varied until the corresponding deflection angle calculated by the SDM is reached. The IDM consists of an inverse boundary layer- and an inverse potential theory method. Along the suction side the shape factor of the boundary layer is prescribed conveniently for the laminar and turbulent part. The velocity distribution at the outer edge of the boundary is calculated by an inverse boundary layer method. On the pressure side the velocity distribution is chosen in such a way that a corresponding circulation is realized for turning the flow. Finally, the whole geometry of the cascade is calculated by the inverse potential theory method.

The examination of one cross section is done numerically using the commercial RANS Solver ANSYS CFX. Low Reynolds number of approximately 4.25 × 105 and the transition from laminar to turbulent are taken into account by the transition SST model.
Gas Carry-Under in Gas-Liquid Cylindrical Cyclone Separator: A Mechanistic Model
Authors: Kolla Srinivas Swaroop , Mohan Ram S. , Shoham Ovadia
Published: November 2019

Gas Carry-Under (GCU) is one of the two undesirable phenomena that occur in the GLCC©,1 (Gas-Liquid Cylindrical Cyclone) separators when it operates even within the Operational Envelope (OPEN). Earlier studies have shown that maintaining a liquid level below the inlet of the GLCC under control configuration affects the GCU in GLCC. It has been identified that the tangential wall jet is the cause of gas entrainment within the GLCC and has been understood to change with liquid level maintained at the inlet. Also, it has been theorized that effective formation of the vortex formed in the lower part of the GLCC, or a stable gas core enhances the separation of gas entrained in the liquid. At present, there is no mechanistic model which captures these complex physical phenomena in the GLCC. This paper presents a newly developed mechanistic model which can predict the GCU for different flow conditions, fluid properties, and various liquid levels. The proposed model captures the various physical phenomena namely: saturated flow at the inlet, tangential wall jet phenomena, gas entrainment and vortex flow that results in separation of gas. The developed model has been compared with the extensive experimental data and is said to be in good agreement.
Numerical Simulation of Supercritical Octane Flows in a Heated Circular Tube With Simple Thermal Cracking Model
Authors: Furusawa Takashi , Taki Noriyuki , Yatsuyanagi Shuto , Yamamoto Satoru , Miyaura Takuto , Tomioka Sadatake
Published: November 2019

Supercritical octane flows that undergo thermal cracking in a heated circular tube were numerically investigated using our numerical methods based on the preconditioning method solving the compressible Navier–Stokes equations with the thermophyical properties from the Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). The simple thermal-cracking model for octane was developed from the results calculated by KUCRS and Cantera software, assuming mild cracking condition and single-fluid flow. Supercritical octane flows were simulated under wall temperatures that would and would not encourage thermal cracking. Slight temperature differences affected the velocity distribution in the heated pipe because of the change in density. In low-wall-temperature conditions without thermal cracking, the simulated outlet temperatures were in good agreement with experimental results. Octane near the heated wall was decomposed by thermal cracking in the high wall temperature conditions. The wall temperature and the residual time affected the conversion rate of the thermal-cracking conversion rate. The present numerical methods underestimated the experimentally measured conversion rate, though the rough trends of the conversion rates were captured.
Inter-Blade Vortex Characteristics With the Blockage Effects of Runner Blade in a Francis Hydro Turbine Model
Authors: Kim Seung-Jun , Kim Jin-Hyuk , Choi Young-Seok , Cho Yong , Choi Jong-Woong
Published: November 2019

This study presents the numerical analysis on the inter-blade vortex characteristics along with the blockage effects of runner blade in a Francis hydro turbine model with various flow rate conditions. The turbine model showed different flow characteristics in the runner blade passages according to operating conditions, and inter-blade vortex was observed at lower flow rate conditions. This inter-blade vortex can lead to performance reduction, vibration, and instability for smooth operation of turbine systems. The previous study on blockage effects on various runner blade thickness, showed its influence on hydraulic performance and internal flow characteristics at low flow rate conditions. Therefore, the inter-blade vortex characteristics can be altered with the blockage effects at low flow rate conditions in a Francis hydro-turbine. For investigating the internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations are performed. These inter-blade vortices were captured at the leading and trailing edges close to the runner hub. These vortex regions showed flow separation and stagnation flow while blockage effects contributed for decreasing the inter-blade vortex at low flow rate conditions.
Wavenumber-Frequency Spectrum Analysis of Pressure Fields Around an Automobile
Authors: Wang Xifeng , Mizushiri Kenta , Yokoyama Hiroshi , Iida Akiyoshi
Published: November 2019

In order to evaluate the interior noise caused by the flow around automobiles, it is necessary to clarify the nature of the pressure fluctuations on the surface of vehicle body. The pressure fluctuations around the vehicle which are caused by the fluid motion can be solved by unsteady-compressible Navier-Stokes equation. However, the differences between the scales and intensity of the pressure fluctuations related to the hydrodynamic pressure fluctuation (HPF) of the flow field and the aerodynamic sound (acoustic pressure fluctuation APF) are quite large, these phenomena can be considered separately as two different phenomena. This assumption can help us to understand the contributions of these two components of pressure fluctuations to the structural vibration and interior sound of automobiles. Since both the HPF and the APF are pressure fluctuations, they cannot be separated only by measuring with a single pressure sensor.

In this study, we divided these pressure fluctuations by using wavenumber-frequency spectrum analysis. Wind tunnel experiment showed that the HPF and the APF have different wavenumber fields in the wake of a rear-view mirror, and the intensity and wavenumber of the HPF are larger than that of the APF. Flow field was also investigated by using the incompressible flow simulation. As a result of wavenumber-frequency spectrum analysis based on the pressure fields around the vehicle body, the HPF and the APF have different wavenumbers in the case of a boundary layer flow field with no separation such as boundary layer on the vehicle roof. On the other hand, very small wavenumber components of the HPF were observed in the recirculation flow around the rear-view mirror downstream, despite incompressible simulation was done. This is probably due to the flow fields excite the vehicle body in the direction close to the vertical with respect to the vehicle body surface (side shield) in the separated flow region, and the wavenumber vector project on the shield surface apparently become smaller. The wavenumber vector becomes short but the frequency is constant, which leads the speed of pressure propagation apparently increases.

In the reverse flow region, even if the uniform flow velocity is smaller than the speed of sound, the HPF may still contribute to vibration and sound generation. At the same time, since the flow velocity is actually slowed in the reverse flow region, large wavenumber components were also observed. Therefore, the wavenumber spectrum was observed in a wide range of the wavelength region.

In conclusion, by investigating the wavenumber frequency spectrum, it is possible to estimate the flow field contributing to the interior noise of automobiles.
Stabilizing Pump-Turbine Operations Using Water Injection Passive Control
Authors: Altimemy Muhannad , Attiya Bashar , Daskiran Cosan , Liu I-Han , Oztekin Alparslan
Published: November 2019

Computational fluid dynamics simulations are carried out to characterize the spatial and temporal characteristics of the velocity and pressure field of turbulent flows through a pumpturbine unit operating with the turbine mode. The high-fidelity large eddy simulations turbulence model is utilized to examine the flow-induced vibrations in the draft tube of the unit. The water injection from the runner cone is considered as the control strategy to mitigate the flow-induced fluctuations. The simulations are conducted for the turbine flow rate of 0.2 m3/s without and with the water injection at a rate of 0.008 m3/s. The pressure along the surface of the draft tube is probed at various locations to access the effectiveness of the water injection to mitigate fluctuations. Water injection at 4% rate is demonstrated to be effective in attenuating the pressure fluctuation inside the draft tube. The amplitude of fluctuations is reduced by nearly 50% by the water injection. The generated power is hardly influenced by water injection. Thus, the control strategy considered here could be employed effectively without a penalty on the power generation.
Effects of Trailing Edge Position of Splitter Blade on the Pressure Pulsation in a Low Specific Centrifugal Pump
Authors: Zhang Jinfeng
Published: November 2019

A combination of experimental and numerical simulation was carried out to analyze influence of trailing edge position of splitter blade on the pressure fluctuation in low specific pumps with and without splitter blades under different flow rates. Performance experiments and PIV tests were performed to verify the results of numerical calculation. Several monitor points were placed in the calculation model pump to collect the pressure fluctuation signals, which were processed by Fast Fourier Transform to obtain the frequency results for further analysis. Besides, turbulence intensity and relative velocity distribution were also analyzed in regions of impeller and volute. The results showed that compared with prototype without splitter blade and the splitter blade schemes, when the trailing edge of splitter blade deviates to the suction side of main blade, the maximum pressure pulsation amplitudes are the lowest at different monitoring points of model pump. And the variation of pressure pulsation amplitude in this scheme is relatively stable with the change of flow rates compared with other schemes. Furthermore, the splitter blade scheme with an appropriate trailing edge position has the lowest average turbulence intensity and optimal relative velocity distribution in main flow passage component. Therefore, this paper proposes a reference scheme of the trailing edge position of the splitter blade to effectively decrease predominate pressure pulsation amplitude.
Experimental Approach to Predict the Residual Axial Thrust in Centrifugal Pumps
Authors: Elicio Giulio , Annese Francesco
Published: November 2019

The residual axial thrust of a centrifugal pump is the vector resultant of the hydraulic components of impellers and sleeves, the momentum force and other imbalance forces and is bear by the thrust bearing. Among all the components, the hydraulic is by far the most important because it is typically one order of magnitude bigger than the others and the final residual axial thrust itself; but it is also the most difficult to calculate or estimate. This is mainly due a lot of uncertainties in the definition of the pressure distribution in the sidewall gap, dependent on the rotational speed, the leakages through the annular seals, the inlet swirl to the sidewall, the axial alignment of the impeller with the stator, the geometric tolerances and the pump operation.

In this paper an experimental approach to validate and calibrate the formulation to predict the hydraulic component of the impellers is presented. The typical formulation to evaluate the parabolic behavior of the pressure distribution is based on a series of coefficients, coming from literature, to consider all the above-mentioned influences. This formulation can be considered satisfying when dealing with pumps with back-to-back arrangement of the impellers on the rotor, since the hydraulic components are almost balanced. But with in-line configuration, all the hydraulic components of the impellers act against one direction and most of their force can be balanced by means of a balance drum, much more reliable than a balance disk. An experimental test campaign on a high energy diffuser pump was performed. The pump was equipped with load cells and temperature probes on the thrust bearing, and a special balancing line with a regulating bleed-off valve whose aim was to partialize the flowrate routed from the back side of the balancing drum to the suction. By throttling the bleed-off valve, it was possible to measure the hydraulic components of the impellers in very different operating conditions of the balancing drum, at different rotational speed and at different flowrates included zero residual axial thrust capability. As results of this campaign, once calibrated the coefficients on the full-scale pump, it is possible to calculate the residual axial thrust based on specific pressure measurements of the model test of a stage hydraulic; this also allows a thorough optimization of the thrust bearing selection.
Flow Field and Performance Analysis of a Centrifugal Pump During Unstable Operating Conditions
Authors: Prunières Romain , Kato Chisachi
Published: November 2019

Centrifugal pump performance curves instability, characterized by a local dent, can be the consequence of flow instabilities in rotating or stationary parts. Such flow instabilities often result in abnormal operating conditions, causing severe problems such as increased pressure pulsation, noise and vibration which can damage both pump and system. For the pump to have reliable operation, it is necessary to understand the onset and the mechanism of the phenomenon resulting in performance curves instability.

Present paper focuses on performance curves instability of a centrifugal pump of low specific speed (ωs = 0.65, Ns = 1776) and aims at a better understanding of the mechanism leading to the head drop observed during tests at part load. For that purpose, Computation Fluid Dynamic (CFD) was performed using a Large-Eddy Simulation (LES) approach. The geometry used for present research is in fact the first stage of a multi-stage centrifugal pump and is composed of a suction chamber, a closed-type impeller, a vaned diffuser and return guide vanes to next stage (not included). Leakages at wear ring and stage bush were also included in the computed geometry in order to consider their potential influence on pump stability.

The occurrence of the instability in CFD is found at a higher flow rate than in the experiments. It is observed that the pre-swirl angle is under-predicted by several degrees which leads to change the impeller operating conditions.

Nevertheless, the analysis of the CFD results is still useful to have a better understanding of the onset of the head drop. When the head drops, a switching of low radial and axial velocities at the impeller outlet from the hub side to the shroud side is observed. This change of flow pattern goes along with a strong increase of the diffuser inlet throat recirculation and the development of stall, that impairs pressure recovery between the impeller outlet and the diffuser inlet.

As the pump flow rate is further decreased below the head drop flow rate, recirculation at the diffuser throat extend toward the impeller outlet and impact Euler head. Conversely, the pressure recovery from the impeller outlet to the diffuser inlet throat increases again as the flow velocity slowdown can be effective again. Consequently, the pump head increases again.
Phototactic Behaviour of Active Fluids: Effects of Light Perturbation on Diffusion Coefficient of Bacterial Suspensions
Authors: Vourc’h Thomas , Léopoldès Julien , Peerhossaini Hassan
Published: November 2019

Active fluids refer to the fluids that contain self-propelled particles such as bacteria or micro-algae, whose properties differ fundamentally from the passive fluids. Such particles often exhibit an intermittent motion; with high-motility “run” periods separated by low-motility “tumble” periods. The average motion can be modified with external stresses, such as nutrient or light gradient, leading to a directed movement called chemotaxis and phototaxis, respectively.

Using cyanobacterium Synechocystis sp.PCC 6803, a model micro-organism to study photosynthesis, we track the bacterial response to light stimuli, under isotropic and non-isotropic conditions. In particular, we investigate how the intermittent motility is influenced by illumination.

We find that just after a rise in light intensity, the probability to be in the run state increases. This feature vanishes after a typical time of about 1 hour, when initial probability is recovered. Our results are well described by a model based on the linear response theory.

When the perturbation is anisotropic, the characteristic time of runs is longer whatever the direction, similar to what is observed with isotropic conditions. Yet we observe a collective motion toward the light source (phototaxis) and show that the bias emerges because of more frequent runs towards the light.
Research of Unsteady Characteristics of Torque in Centrifugal Pumps
Authors: Yin Luo , Yuejiang Han , Jian Dong
Published: November 2019

Torque is one of the most important operating parameters of centrifugal pumps which reflects the internal flow rate of centrifugal pumps. In order to explore the unsteady characteristics of torque of centrifugal pumps based on sensorless monitoring technology, a series of accurate measurements of torque of experimental centrifugal pump were carried on based on the test data collected. The frequency characteristic spectrums of torque were established and analyzed under different operation conditions. The analysis results shows that the torque of the experimental centrifugal pump varies approximately linearly with the increase of flow rate in time domain. Besides, a gentle trend of the torque fluctuation is also founded. Through frequency domain, the analysis results show that the dominant frequencies under different flow rates and cavitation conditions are all axial frequencies. The magnitude of amplitude has nothing to do with the flow rates or the cavitation conditions, and the internal flow rates of centrifugal pumps have no obvious effects on the fundamental frequency of torque of centrifugal pumps.
Research on the Condensation Process of Gaseous Water and Water/Ethanol Mixture in the Laval Nozzle
Authors: Bian Jiang , Cao Xuewen
Published: November 2019

Condensation phenomenon has been studied actively for decades because of its extensive and significant applications in various fields of technology and engineering. The condensation phenomenon of condensable component in supersonic flows is still not understood very well as a result of the complex nucleation and droplet growth process, especially the condensation characteristic of gas mixture. In this paper, the Laval nozzle was designed based on the bi-cubic curve, state equation of real gas, arc plus straight line and viscous correction of boundary layer. The physical and mathematical models were developed to predict the condensation process in the supersonic air flows based on the nucleation and droplet growth theories, surface tension model and gas-liquid governing equations. The condensation processes of gaseous water/air binary (single condensable) gas and water/ethanol/air ternary (double condensable) gas mixture in the designed nozzle were simulated, and the reliability of the established models was verified by the experimental data. By comparing the condensation process of water/air binary gas with water/ethanol ternary gas, the influence of the second condensable component on the condensation process was analyzed. The results show that in the condensation process of gaseous water, as the pressure and temperature of water vapor decrease in the nozzle, spontaneous condensation occurs further downstream the nozzle throat. The nucleation rate grows rapidly from 0 to peak in a very short distance. With the consumption of water vapor, due to the decrease of the degree of supercooling, the nucleation environment is destroyed, and the nucleation rate quickly decreases to 0. The nucleation process is rapid in time and space, while the droplet growth process could maintain longer. The droplet number and mass fraction increase continuously till the nozzle outlet. There is a weak condensation in the nozzle due to the release of latent heat, but it is not obvious because the air acts as a heat container and absorbs the latent heat released by condensation.

In the water/ethanol/air ternary system, the ethanol nucleates prior to water vapor. With the increase of supercooling, water vapor also begins to nucleate. In essence, there are two kinds of condensation nuclei (water nuclei and ethanol nuclei), and both the water and ethanol vapor can aggregate on these two kinds of condensation nuclei. Compared with the condensation process of water, the Wilson point of condensation is closer to the throat and the outlet mass fraction of liquid phase is greater in the condensation process of water/ethanol mixture, which shows that the water and ethanol can affect and promote each other. The maximum nucleation rate, droplet growth rate, droplet radius and outlet mass fraction of liquid phase of water/air binary and water/ethanol/air ternary mixture are about 9.46 × 1026 m−3s−1 and 2.57 × 1027 m−3s−1, 1.65 × 10−5 m/s and 1.02 × 10−5m/s, 1.32 × 10−7m and 1.63 × 10−7m, 0.19% and 1.34%, respectively.
Visualization of Three-Dimensional Flow Structures Caused by Rotating Instability
Authors: Peter Julija , Thamsen Paul Uwe
Published: November 2019

The present study deals with the flow phenomenon Rotating Instability (RI), which is predominantly observed in axial compressors at off-design conditions e.g. near stall. It potentially induces noise and triggers blade vibrations. Despite numerous studies, the characteristics and the source of RI are not completely understood. The objective of this work is to identify and to visualize characteristic flow topology corresponding to RI by means of Stereo High Speed Particle Image Velocimetry (PIV). The experimental investigations were carried out in an annular compressor stator cascade with and without hub clearance at an inflow Mach number of Ma = 0.4 and the Reynolds number of Re = 300 000. The time-resolved 3C flow field is measured in a single blade passage in planes tangential to the hub. Additionally, the time-resolved pressure fluctuations are captured synchronously to the PIV system. By using combined correlation techniques the spectral characteristics, the spatial extension of the RI and the characteristic flow structures were identified and visualized in configurations with and without hub clearance. The investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without hub clearance. Overall, this work gives important insights into the complex phenomenon Rotating Instability, which can be taken into account when developing compressors in the future.
Numerical Simulations of a Centrifugal Pump With a Non-Newtonian Fluid: Influence on Performances of Different Rheological Modelling
Authors: Occari Matteo , Mazzanti Valentina , Mollica Francesco , Munari Enrico , Pinelli Michele , Suman Alessio
Published: November 2019

Centrifugal pumps change their performance with respect to water when processing non-Newtonian fluids. Many aspects about pumping of non-Newtonian fluids remain to be clarified due to complexity of the matter and the scarcity of investigations. In addition to experimental tests, in recent years some CFD fluid dynamics simulations have been realized to analyze the performance of centrifugal pumps with non-Newtonian fluids. Knowledge of rheology is required to correctly simulate the fluid inside the pump and predict the performance. The aim of this work is to emphasize the criticalities in the simulation of centrifugal pumps with non-Newtonian fluids, since, starting from the same rheological data, can be deduced different rheological laws, however reliable, that produce different effects on the simulations. In this paper, the performances of a model pump were measured experimentally with pear juice and accompanied by the rheological characterization of the fluid. Subsequently, the pump was simulated using five different rheology laws, all fitted to the same experimental rheogram, that differ from each other in predicting viscosity out of shear rate range experimentally measured. The pump performances were affected by the different rheology implemented. The simulations showed that the shear rates developed inside the pump are much higher than those measured with the rheometer. Consequently is necessary to achieve higher shear rates in the experimental rheogram to make sure to correctly model the rheology for shear rates values typically present in the pump.
LBM Simulations of Dispersed Multiphase Flows in a Channel: Role of a Pressure Poisson Equation
Authors: Horwitz Jeremy A. K. , Vanka S. P. , Kumar P.
Published: November 2019

In recent years, Lattice Boltzmann Methods (LBM’s) have emerged as a popular class of paradigms for the simulation of multiphase flows. These methods rely on discretized Boltzmann equations to represent the individual multiphase species. Among LBM’s advantages is its ability to explicitly account for interfacial physics and its local streaming/collision operations which make it ideally suited for parallelization. However, one drawback of LBM is in the simulation of incompressible multiphase flow, whereby the density should remain constant along material characteristics. Because LBM uses a state equation to relate pressure and density, incompressibility cannot be enforced directly. This is true even for incompressible single-phase LBM calculations, in which a finite density drop is needed to drive through the flow. This is also the case for compressible Navier-Stokes algorithms when applied to low Mach number flow. To mitigate compressibility effects, LBM can be used in low Mach regimes which should keep material density variation small. In this work, we demonstrate that the assumption of low Mach number is not sufficient in multiphase internal flows. In such flows, in the absence of a Pressure Poisson constraint to enforce incompressibility, LBM predicts a compressible solution whereby a density gradient must develop to conserve mass. Imposition of inflow/outflow boundary conditions or a mean body force can ensure that mass is conserved globally, thereby quelling density variation. The primary numerical problem we study is the deformation of a liquid droplet immersed in another fluid. Though LBM is not typically conducted with a pressure Poisson equation, we incorporate one in this work and demonstrate that its inclusion can significantly lower the density variation in view of maintaining an incompressible flow.
A Computational Heat Transfer and Optimization Study of Drying of Peas and Rice in a Rotary Dryer
Authors: Singh Atinder Pal , Ghoshdastidar P. S.
Published: November 2019

The paper reports a numerical simulation study of drying of peas and rice grains in a rotary dryer with superheated steam, dry air, and humid air (20%, 40%, 60% and 80% moisture content by volume) at 1 bar as the drying media. The initial water contents in peas and rice grains are 75% and 13% (by weight), respectively. The thermal model includes turbulent convection heat transfer from the gas to the refractory wall and solids, radiation exchange among the gas, refractory wall and the solid surface, conduction in the refractory wall, and mass and energy balances of the gas and the solids. In the absence of experimental data of food drying, the present model has been satisfactorily validated with the experimental and numerical results reported in Sass (1967, Sass, A., “Simulation of Heat-Transfer Phenomena in a Rotary Kiln”, Industrial & Engineering Chemistry Process Design and Development, 6(4), pp. 532–535) for iron ore and cement. It is found that for superheated steam there is an optimum kiln inner diameter at which the predicted kiln length is the highest. For dry air, the predicted kiln length monotonically decreases with a decrease in kiln inner diameter. A detailed parametric study lent a good physical insight into the drying process. An optimization study has been conducted for superheated steam as the drying medium using the Univariate Search method to minimize the length of the kiln with an upper limit on the inlet gas temperature as the constraint.
Theoretical Analyses of the Number of Backflow Vortices on an Axial Pump or Compressor
Authors: Ito Yu , Sato Yuhei , Nagasaki Takao
Published: November 2019

This paper presents theoretical analyses of flow fields on an axial pump or compressor, where the main flow enters from one side of the cylindrical casing, whereas an axially reverse and tangentially whirling flow enters from the tip clearance between the casing and the impeller, which sucks in the mixed flow. In this flow field, several secondary vortices exist in the mixing zone across the contact surface between the main and the axially reverse tangentially whirling flow. This type of secondary vortex is called a “backflow vortex.” The backflow vortices are tornado-like, parallel to the casing axis, and periodically distributed on the contact surface; they revolve around the casing axis and rotate around themselves. Regarding the backflow vortices, the relationships between their number (N), revolving diameter (d), revolving angular velocity (ω), and the ratio of the forced vortex region to the distance between the secondary-vortex center and the cylindrical wall (f) were all theoretically investigated. The five major findings are as follows: First, between d, ω, N, and f, any parameter can be determined if the other three are specified. Second, ω decreases, N increases, or f increases when d is increased and the other two are fixed. Third, d decreases, N increases, or f increases when ω is increased and the other two are fixed. Fourth, d increases, ω increases, or f decreases when N is increased and the other two are fixed. Fifth, d increases, ω increases, or N decreases when f is increased and the other two are fixed. To validate these theoretical results, “backflow vortex cavitation,” which occurs around the center of the backflow vortices on a rotating inducer as a representative of axial pumps or compressors, was observed. The backflow vortex cavitation is visible; therefore, d, ω, and N become quantitatively measurable. The test inducer was a triple-threaded helical inducer with a diameter of 65.3 mm and a rotational speed range of 3000–6000 rpm. It was experimentally confirmed that the proposed theoretical analysis is true.
High-Speed Flow Visualization of a Canonical Airblast Atomizer Using Synchrotron X-Rays
Authors: Heindel Theodore J. , Morgan Timothy B. , Burtnett Thomas J. , Bothell Julie K. , Li Danyu , Aliseda Alberto , Machicoane Nathanael
Published: November 2019

Liquid sprays play a key role in many engineering processes and the dynamics at the nozzle exit have a significant impact on the downstream spray characteristics. However, visualizing the spray in this region is extremely challenging because, under most operating conditions, the spray is optically dense. High intensity white beam X-rays, like those found at the Advanced Photon Source (APS) at Argonne National Laboratory, can be used to produce time-resolved measurements of the liquid-gas structures in the spray near-field region. In this study, high temporal and spatial resolution X-ray images were acquired at the 7-BM beamline at APS of an atomization process using a canonical airblast atomizer consisting of coaxial liquid and gas jets. Unique flow structures were observed under various operating conditions, including bag, ligament, wisp, droplet, and air bubble formation, as well as hollowing of the liquid core into a crown at the liquid needle exit. Conditions where these structures exist are presented and their impact on spray formation are discussed.
Numerical Study for Effect of Staggered Wire Electrodes in a Electrostatic Precipitator
Authors: Choi Hoyeon , Park Yong Gap , Ha Man Yeong
Published: November 2019

In this paper, a numerical model was developed to describe the wire-plate electrostatic precipitator, commonly called electronic air cleaners. Electrostatic precipitator have been widely used to control particulate pollutants, which adversely affect human health. In this model, the complex interactions between fluid dynamics, electric fields and particle dynamics are considered. Therefore different approach methods are used in this study for each field, Eulerian reference frame was used for the fluid flow field and the electric field, Lagrangian reference frame used for the particles trajectories. In order to describe corona phenomena around high voltage electrode, electric field and ion current density field in electrostatic precipitator are numerically calculated using the iterative method for corona discharge model suggested by Kim (2010). The most important concept in electrostatic precipitator is the electric force applied to particles through the particle charging phenomena. The charge acquired by the particle in the corona region was obtained by combining the field charge, the diffusion charge and the time available for charging being the residence time of the particle in the corona region. In order to simulate more accurately, the charging model suggested by Lawless (1996) is used for the charging phenomena of particles by corona discharge because this model was designed to predict combination effect of diffusion charge and field charge. The diminution of particle concentration along the collection plate was derived from Deutsch’s theory, and migration velocity of the particle was developed from the condition that the magnitude of Coulomb force is equal to that of Stoke’s resistance force. This model is implemented by UDF in commercial software Fluent and validated with experimental and numerical results from literatures. CFD results had been compared with various experimental data obtained by Penney&Matick, Parasram and Kihm. Our results shows good agreement in terms of distributions of electric potential, current density, electrohydrodynamic flow pattern, and particle trajectories as well as corona current and collection efficiency. From this simulation, the effect of wire arrangement on electrostatic precipitator characteristics and particle charging are investigated. Both inline and staggered arrangements of wire electrode have been considered for fixed values of gas velocity equal to 2m/s. Applied voltage on wire electrode varies 6∼13kV and particle diameter is 4μm. For low voltage condition, staggered arrangement of wire electrode caused the turbulent effect so that collection efficiency increase more than inline arrangement. However, collection efficiency decrease in high voltage condition because electric force applied on particles passing between the wire electrodes is canceled out by both side wire electrodes.
Computational Fluid Dynamics to Assess the Blade Effect of a New Savonius Rotor for Improvement of the Output Power Coefficient
Authors: Matsui Takanori , Fukui Tomohiro , Morinishi Koji
Published: November 2019

The output power coefficient of the Savonius rotor should be improved for better practical applications. So far, new Savonius rotor has been developed to improve the minimum output coefficient by adding semi-elliptical blade. Thus, the purpose of this research is to investigate the influence of the additional semi-elliptical blade’s position on the output coefficient. Flow around the rotor was simulated by using the regularized lattice Boltzmann method. The virtual flux method was used to express the shape of the rotor on a Cartesian grid, and the multi-block method was used for local fine grids of the rotor. The rotation speed of the Savonius rotor was maintained constant, and its performance was evaluated by the output power and torque coefficients. As a result, the semi-elliptical blade successfully generated additional positive torque in the range of the advancing phase and improved the minimum output power coefficient of the rotor during a cycle. When the moment arm is short, the semi-elliptical blade did not generate large negative torque in the range of the returning phase owing to its position behind the main blade in the wind flow direction. The output power coefficient of the new Savonius rotor was improved compared to that of the traditional one depending on the length of the semi-elliptical blade’s moment arm.
The Reynolds Stress in Channel Flows From a Lagrangian Treatment of the Turbulence Momentum
Authors: Lee T.-W.
Published: November 2019

We have developed a mechanistic approach for determination of the Reynolds stress, using a Lagrangian analysis of turbulent momentum. Analysis and comparison with DNS and experimental data point toward the soundness of this approach (Lee, 2018). von Karman constant, the inner layer thickness and the Reynolds stress itself are all recovered through this approach, in agreement with DNS data. In addition, the turbulent flow profiles can be calculated iteratively using the basic Reynolds-averaged Navier-Stokes equation, in conjunction with the current transport equation for the Reynolds stress. In this work, we explore these and further uses of the current approach in solving turbulent flow dynamics.
Investigation and Analysis of the Flow Field Induced by a Symmetrical Suction Elbow at the Pump Inlet
Authors: Muntean Sebastian , Bosioc Alin Ilie , Drăghici Ionel Aurel , Anton Liviu Eugen
Published: November 2019

The pump inlet casing deflects the fluid flow from the inlet pipe, mainly arranged normally to the axis, into the axial direction. The pump inlet casing can take a large variety of geometrical shapes from curved pipes to three-dimensional elbows. The hydrodynamic field induced by symmetrical suction elbow (SSE) at the pump inlet is experimentally investigated in order to quantify it effects at the pump inlet. The pump test rig and the experimental setup are detailed. A SSE model is installed at the pump inlet. Laser Doppler Velocimetry (LDV) measurements are performed on the annular cross section located at the pump inlet. As a result, the map of the velocity field is determined quantifying the non-uniformities induced by SSE. Next, the full 3D turbulent numerical investigation of the flow in the SSE is performed. The numerical results on the annular cross section are qualitatively and quantitatively validated against LDV data. A good agreement between numerical results and experimental data is obtained. The hydrodynamic flow structure with several pairs of vortices is identified examining the vorticity field. However, two pairs of vortices with largest contribution to the flow non-uniformity are examined. Three parameters are considered to quantify the evolution of each vortex center: two geometrical quantities (e.g. the radial and angular coordinates) and one hydrodynamic (the magnitude of vorticity). The largest values of the vorticity magnitude are identified in the center of both vortices located behind the shaft. The 3D distribution of the vortex core filaments is visualized. As a result, the 3D geometry of the SSE and the pump shaft are identified as the main sources of the flow non-uniformity at the pump inlet. This deep analysis of the 3D flow field induced by the SSE paves the way towards an improved geometry with practical applications to real pump and pump-turbines.
Parametric Study for Optimization of Blowing and Suction Locations for Improving Lift-to-Drag Ratio on a Clark-Y Airfoil
Authors: Ohashi Masahiro , Morita Yuki , Hirokawa Shiho , Fukagata Koji , Tokugawa Naoko
Published: November 2019

In this study, Reynolds-averaged Navier-Stokes simulation (RANS) of the uniform blowing and suction (UB/US) control on a Clark-Y airfoil was performed aiming at improving an airfoil performance by friction drag reduction. First, the control effect when only the uniform blowing control or uniform suction control is applied on the airfoil surface was investigated by changing the control locations. The blowing or suction velocity was 0.14% of the free-stream velocity and the blowing/suction area was set at four different locations from the leading edge to the trailing edge on both the upper and lower surfaces. The Reynolds number based on the chord length is 1.5 × 106. The angle of attack is set to 0°. It was found that friction drag is decreased/increased by single UB/US control. It was also found that the lift-to-drag ratio improved with UB on the lower surface or US on the upper surface, and decreased with UB on the upper surface or US on the lower surface. In the combined control of UB and US, the blowing and suction velocity was 0.14% or 0.26% of the free-stream velocity and the locations of blowing/suction and flow conditions were the same as those in the cases with either UB or US. It seemed that the lift-to-drag ratio was improved by the combined control of UB on the lower surface and US on the upper surface. In particular, the lift-to-drag ratio was most improved by US on the lower rear surface and UB on the upper rear surface.
Gas Wall Layer Experiments for SNS Target
Authors: Weinmeister Justin R. , Dominguez-Ontiveros Elvis E. , Barbier Charlotte N.
Published: November 2019

The Proton Power Upgrade (PPU) project will increase the proton beam power at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL), requiring new cavitation erosion mitigation techniques for the mercury target vessel. More precisely, a gas wall layer will be injected on the wall surface where heavy cavitation erosion is observed. In this paper, a series of experiments were performed to develop a gas layer on a simplified target geometry. First, experiments in water were used to test a prototype injection strategy in a simplified target nose geometry. Then the experiment was repeated at the Target Test Facility (TTF) at ORNL where mercury wass flowed in the same geometry. Observations showed that gas injection into liquid metal was much more sensitive to flow velocity than in water. Ultimately, the experiments showed the gas injection must be located very close to the area of interest in a non-intrusive configuration to reduce shear stresses in the flow for good gas coverage. This technique will be next implemented in a more prototypical target.
Flow Visualization and Drag Measurement of a Circular Cylinder in Compressible Flow at Reynolds Number Between 1000 and 5000
Authors: Kusama K. , Noguchi A. , Nagata T. , Komuro A. , Nonomura T. , Ando A. , Asai K.
Published: November 2019

In this study, a compressible low-Reynolds number flow over a circular cylinder was investigated by schlieren visualization and the force measurement. A Reynolds number based on freestream quantities and a diameter of a cylinder is set to be 1000 ≤ Re ≤ 5000 and a Mach number is set to be 0.1 ≤ M ≤ 0.5 by using the low-pressure wind tunnel. From the schlieren visualization, frequency of the vortex shedding was obtained by performing frequency analysis on the time series schlieren images. Near wake structure by the circular cylinder is measured by time-averaged schlieren image. Even though M is less than 0.5, the structure of the flow fields changes depending on M. The effect of M on the scale of wake structure depends on Re. Under the condition at Re of 1000–3000, the scale becomes large as M increases more than 0.2. On the other hand, under the condition that Re is 4000–5000, it becomes small as M increase 0.3 or more St is revealed to be decrease for Re of 2000–3000 with increasing M, and St increases at Re of 4000–5000. From the force measurement, drag coefficient (Cd) and pressure distribution on a circular cylinder (Cp) obtained. The effect of M on Cd does not depend on Re, and Cd also increases as M increases. The effect of Re on Cd is also observed that Cd increases as Re increases and this trend doesn’t depend on M. The Cp decrease with Re increase. The M effect on Cp is that the range of Cp is enlarged with M increase.
Mixing Behavior and Performance of Density Stratification by Gas-Liquid Two-Phase Jet
Authors: Lu Jiarong , Seo Ryutaro , Kaneko Akiko , Abe Yutaka
Published: November 2019

Density stratification is formed in the natural environment such as the lake water system due to the temperature difference of surface water and deep water, leading the damage of lake ecosystem. To dispel the density stratification, several researches in using liquid and gas phase jet to destruct and mix the density stratification was conducted. However, the effect in using gas-liquid two-phase jet to mix the density stratification has not been clarified.

In this study, we performed the mixing experiments of density stratification with stained water and salt water. Based on the visualization method and the image processing, the density changing during the experiment was obtained in quantitatively and the dimensionless density distribution was built. Furthermore, the influence of air lift pipe in mixing was investigated.

From the density distribution, we classified the result into three kinds of mixed behavior by analyzing the temporal transition of density stratification. Additionally, the mixing pattern with air lift pipe connected with the distance between the nozzle and the entrance of pipe.