bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
Visualization of Three-Dimensional Flow Structures Caused by Rotating Instability
Authors: Peter Julija , Thamsen Paul Uwe 
Published: November 2019

Abstract
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

Abstract
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

Abstract
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

Abstract
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.