bluuebunny/crossref_metadata_2025 huggingface dataset:
Drag and Cavity Development of Two Slender Bodies: A Numerical Study
Authors: Jun Yong-Du , Bae Kang-Sik , Lee Seok-Soon , Lee Jong Soo
Published: July 2018

In the present study, an unsteady three-dimensional flow simulation based on the RANS (Reynolds Average Navier-Stokes) equations with k-ε turbulence model and Singhal et al.’s cavitation model is conducted to study the cavity development behavior of two slender bodies, that is, a flat-headed cylinder and a step-headed cylinder of 50 mm in length and 10 mm in diameter. Using so called VOF method to track the liquid-vapor phase interface, time dependent solutions with varying approach speed range from 10 m/s to 55 m/s are obtained and analyzed to provide key information such as cavity initiation speed, drag coefficient and the cavity shape and size (max. length and diameter). The implemented numerical model is validated for flows over a flat disk cavitator against the experimental correlation. According to the present simulation results, slender bodies with two different head shapes, that is, a flat cylinder and a stepped one, respectively, showed very close behavior in their cavity initiation speed, maximum developed cavity diameter and length, but consistently lower drag coefficient with the step-headed cylinder case, which suggests the possible advantage of seeking optimized cavitator shape.
Analysis of Mean Orientation Vector and Mean Curvature in Statistically Steady Turbulent Premixed Combustion
Authors: Kwon Jaesung , Kim Dohyun , Huh Kang Y.
Published: July 2018

Formal governing equations are derived for the mean orientation vector, 〈n〉f, and the mean curvature, 〈∇ · n〉f, in turbulent premixed combustion. Balance is checked to evaluate all component terms and to understand their physical implications in DNS of two test flames. The terms involving ∇T(vn + Sd) and n″(vn + Sd)″ are dominant to determine 〈n〉f through a flame brush and at the leading edge. All listed terms are relevant to determine 〈∇·n〉f, while those involving ∇T2νn+SdΣ′f and (∇·n)″ (vn + Sd)″ become important at the edges. Different trends are observed on the dominant terms for thicker flamelets with the Karlovitz number greater than unity. Further investigation may be required to clarify relative importance of the component terms in different regimes of realistic flame conditions.
Similarity Based Performance Prediction of Organic Rankine Cycle Turbine Using Air Condition Data
Authors: Chen Tao , Zhuge Weilin , Zhang Lei , Zhang Yangjun
Published: July 2018

The Organic Rankine Cycle (ORC) is an effective technology to recover the waste heat of the internal combustion engine (ICE) exhaust gas and coolant water. Performance prediction and matching of the expander is a key issue, during designing the ORC system. Radial turbines have the advantage in the ORC system for the ICE waste heat recovery because of its small size and high efficiency compared with volumetric expanders. But the ORC turbines design database is insufficient and the organic gas test rig is difficult to be constructed. As a result, this paper, based on similarity theory, establishes a performance prediction method for fully using the mature design and experimental datum of air turbines. By this prediction method, turbine performance can be obtained when its working fluid is changed from the air to the organic gas. Computational fluid dynamics (CFD) solution has been obtained for a calculation example, and the validity of the turbine performance prediction method is demonstrated by comparing the ORC turbine’s predicted performance with the simulated performance. The results show that almost all of the performance parameter’s predictive deviation is less than 5%. This paper comes to a conclusion that designing an R123 gas turbine is similar with designing an air turbine whose rotation rate is twice that of the former, expansion ratio is twice that of the former, power is four times twice that of the former at the same mass flow rate.
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.
Variation of Hydraulic Performance by Impeller Trimming of a Mixed-Flow Pump
Authors: Yang Hyeonmo , Kim Sung , Lee Kyoung-Yong , Choi Young-Seok , Kim Jin-Hyuk
Published: July 2018

One of the best examples of wasted energy is the selection of oversized pumps versus the rated conditions. Oversized pumps are forced to operate at reduced flows, far from their highest efficiency point. An unnecessarily large impeller will produce more flow than required, wasting energy. In the industrial field, trimming the impeller diameter is used more than changing the rotation speed to reduce the head of a pump. In this paper, the impeller trimming method of a mixed-flow pump is defined, and the variation in pump performance by reduction of the impeller diameter was predicted based on computational fluid dynamics. The impeller was trimmed to the same meridional ratio of the hub and shroud, and was compared in five cases. Numerical analysis was performed, including the inlet and outlet pipes in configurations of the mixed-flow pump to be tested. The commercial CFD code, ANSYS CFX-14.5, was used for the numerical analysis, and a three-dimensional Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model were used to analyze incompressible turbulence flow. The performance parameters for evaluating the trimmed pump impellers were defined as the total efficiency and total head at the designed flow rate. The numerical and experimental results for the trimmed pump impellers were compared and discussed in this work.
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.
Investigation of Wire Effect in a Wire-Wrapped 37-Pin Fuel Assembly
Authors: Jeong Jae-Ho , Yoo Jin , Lee Kwi-Lim , Ha Kwi-Seok
Published: July 2018

The wire effect in a wire-wrapped 37-pin fuel assembly mock-up of a Japanese loop-type sodium-cooled fast reactor (SFR), Monju, has been investigated through a numerical analysis using a general-purpose commercial computational fluid dynamics (CFD) code, CFX. Complicated and vortical flow phenomena in the wire-wrapped 37-pin fuel assembly were captured by a Reynolds-Averaged Navier-Stokes (RANS) flow simulation with a shear stress transport (SST) turbulence model. The CFD results show good agreement with Rehme’s friction factor correlation model, which can consider the number of wire-wrapped pins in the fuel assembly. Three-dimensional multi-scale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Large-scale and small-scale vortex structures are generated in the corner and edge, and interior sub-channel, respectively. The behavior of the large-scale vortex structures in the corner and edge sub-channel are closely related to the relative position between the hexagonal duct wall and the wire spacer. Regardless of the relative position between the adjacent rod and wire spacer, a small-scale vortex is axially developed in the interior sub-channels. Furthermore, a driving force on each wire spacer surface is closely related to the relative position between the hexagonal duct wall and wire spacer. It is expected that the multi-scale vortex structures in the fuel assembly play a significant role in the convective heat transfer characteristics.
Static Pressure Measurement Error of Wall Tap on Throat of Flow Nozzle for High Reynolds Number
Authors: Furuichi Noriyuki , Terao Yoshiya
Published: July 2018

A pressure measurement error using wall tap in a flow nozzle is examined in high Reynolds number. The pressure measurement error is estimated using measurement result of a discharge coefficient of the flow nozzle. The behavior of the differential pressure measurement error is clearly influenced by the tap diameter and the viscosity of the working fluid. To obtain the universal relation, several plots between the pressure measurement error normalized by wall shear stress and tap Reynolds number are presented. Finally, the best relation to universalize of the pressure measurement error is newly proposed in this paper.
Wave Dispersion Analysis of Pulsating Flows in a Circular Conduit Using a Lumped Parameter Model
Authors: Chun Sejong , Jin Jonghan
Published: July 2018

Wave dispersion is a key element in understanding the pulsating flows in a circular rigid pipe. This study suggests that an extended Taylor’s frozen field hypothesis should make the lumped parameter model be more practical because pressure instead of pressure gradient can be measured with simpler instrumentation. Lumped parameter model as well as wave dispersion is introduced, and then some experimental results with a blood flow simulator were analyzed to validate its idea.
An Experimental Investigation on Thermal-Hydraulic Interaction Between Core Makeup Tank and Safety Injection Tank of an Integral Small Reactor During a Small Break Loss-of-Coolant Accident
Authors: Bae Hwang , Ryu Sung Uk , Ryu Hyo Bong , Kim Woo Shik , Yi Sung-Jae , Park Hyun-Sik
Published: July 2018

A passive injection test was conducted using a core makeup tank (CMT), a safety injection tank (SIT) and an automatic depressurization system (ADS), which consists of a passive safety system (PSS) of the SMART reactor. This paper investigates the thermal-hydraulic interaction between CMT and SIT during sequential injections of coolant from these two tanks to a high-temperature and high-pressure reactor pressure vessel using an integral effect test facility of SMART-ITL (System-Integrated Modular Advanced ReacTor-Integral Test Loop). Both CMT and SIT were connected to the reactor pressure vessel by a pressure balance line (PBL) and injection line (IL). A steady-state condition was maintained for 1,000 seconds before the start of the injection. The major parameters agreed well with the target value. After one of safety injection system line was simulated to be broken, a transient injection test was conducted according to the small-break loss-of-coolant accident (SBLOCA) scenario. Coolant injections from a CMT and SIT were started sequentially by opening quick-opening valves installed on the IL and PBL piping, respectively. Several thermal-hydraulic phenomena such as direct contact condensation, thermal stratification, and coupling effects between the CMT and SIT were locally observed during the SBLOCA scenario. The results show that the adopted passive safety injection system functions well as an emergency core cooling system.
Sound Radiation From Two Side-by-Side Rectangular Cylinders With Slightly Different Aspect Ratios
Authors: Octavianty Ressa , Asai Masahito
Published: July 2018

Sound radiation from two side-by-side rectangular cylinders, one of which had a square cross-section and the other had a rectangular cross-section with aspect ratio AR = 1.2 to 1.5, was examined experimentally at Reynolds numbers Re = 1.0 × 104 - 3.3 × 104 in low Mach number flows. The center-to-center distance between two cylinders T/D was 3.6, 4.5 and 6.0. When the center-to-center distance was small, T/d = 3.6, vortex streets from two different cylinders were synchronized with the same frequency as that for a pair of identical square cylinders, even for the cylinder pair of ARs = 1.0 and 1.5. Sound radiation was dipole-like (planar-anti-symmetric), unlike in the case of square-cylinders-pair where sound radiation was in-phase. For larger cylinder spacing T/d = 6, highly modulated sound was radiated with two different frequencies due to non-synchronized vortex shedding from two cylinders.
Simulations of Fully Developed Channel Flow by a New High-Resolution Scheme of the Finite-Difference Lattice Boltzmann Method
Authors: Kunishima Yuichi , Kajishima Takeo , Tsutahara Michihisa
Published: July 2018

This study deals with the aerodynamic noise caused by complex configurations of industrial products. Computational fluid dynamics (CFD) is useful approach to analyze radiated sounds and flows around them. The finite-difference lattice Boltzmann method (FD-LBM) is an expansion of LBM using the finite-difference discretization. It can implement on a body-fitted grid which has been preferably used under the view of computational cost and accuracy. Against huge computational cost in direct simulation of aerodynamic sound, FD-LBM has attained high resolution for sound wave. It is also important to handle turbulence with reasonable computational cost, for flows are often turbulent in engineering applications. We introduced a higher-order upwind biased scheme into the FD-LBM to achieve high resolution for turbulence. We also proposed a procedure to control down the artificial dissipation. We validated the schemes by the simulation of fully developed channel flow (Rτ ≅ 180). Satisfactory results were acquired on the resolutions which were used in direct numerical simulations with conventional CFD methods. The modification was efficacious against lack of resolution on coarser grids.
Near-Wake Flow Structures of a Corner-Chamfered Square Cylinder at Higher Harmonic Excitations
Authors: Aswathy M. S. , Amrita K. K. , Hariprasad C. M. , Kumar R. Ajith
Published: July 2018

In this paper, the results of a flow visualization study on the flow structures around a chamfered square cylinder are presented. Square cylinders having side dimension Bo with corner chamfering ‘b’ are used such that b/Bo ratio assumes values 0, 0.1, 0.2 and 0.3. Corners of the square cylinder are equally cut by a measure ‘b’ both in the stream-wise and cross stream directions. Flow over these cylinders are visualized in a water channel. All the studies correspond to a Reynolds number value of 2100 (based on Bo). Results are taken for two situations (a) cylinders are stationary and (b) cylinders are oscillated at frequency ‘fe’. The main objective of this study is to investigate the near-wake flow structures around the cylinders at harmonic and higher harmonic excitations. Experiments were conducted for fe/fs= 1.0, 1.5, 2.0, 2.5 and 3.0 where fs is the vortex shedding frequency from the stationary cylinder for each b/Bo ratio. Peak-to-peak amplitude of excitation is kept at 1B in all cases. In this investigation, the main focus is on investigating the vortex shedding modes, mechanisms and the number of vortices shed per shear layer as the cylinder completes one oscillatory cycle as a function of fe/fs ratio.
Transonic and Supersonic Flows Past a Rectangular Cavity on Curved Wall
Authors: Ye A. Ran , Das Rajarshi , Kim Heuy Dong
Published: July 2018

Investigations into cavity flows have been conducted for noise/vibration problem created in cavity system. The cavity system has been applied in engineering devices during rapid development of aerospace industry. Cavity on a curved wall has been seldom studied to the author’s best of knowledge. In the present study, the effects of channel shape on the cavity flow field on transonic and supersonic flow is investigated numerically. Time-dependent cavity flow characteristics with oscillating features were examined by using two-dimensional, mass-averaged Navier–Stokes computation based on a finite volume scheme. The results show that pressure loading on the cavity floor is observed to increase with increase in channel curvature for concave channels and decrease for convex channels. Drag in the flow channel increased as channel curvature increased. Unsteady flow characteristics are observed to be more dependent on channel curvature at supersonic free stream velocities.
Validation of Numerical Analysis to Estimate Airfoil Aerodynamic Characteristics at Low Reynolds Number Region
Authors: Lee Donghwi , Nonomura Taku , Oyama Akira , Fujii Kozo
Published: July 2018

In this study, two-dimensional laminar simulation (2-D Lam), two-dimensional Reynolds Averaged Navier-Stokes simulation with the Spalart-Allmaras turbulence model (2-D RANS(SA)), and implicit three-dimensional large-eddy simulation (3-D LES) are performed for NACA0012, NACA0006, and Ishii airfoils at Rec = 3.0 × 104. The relation between a predictability of airfoil aerodynamic characteristics and a dependence of airfoil geometry shape of each numerical method is evaluated at the low Reynolds number. Although little discrepancy is observed for the lift coefficient predictability, significant differences are presented in terms of the separation and reattachment points predictability depending on the numerical methods. The 2-D Lam simulation can predict the lift coefficients as well as the separation and reattachment points qualitatively as similar to the 3-D LES results except for the high angle of attack which is accompanied by the massive separation. The 2-D RANS(SA), the weak nonlinearity and stall phenomena for the lift coefficients are observed. A good predictability of the separation point are shown, however, it cannot be estimated the reattachment points due to the trend to predict widely for the separation region. The predictabilities of each numerical method appear regardless of the airfoil shapes.
Aerodynamic Simulation of Closed-Canopy-Type Parafoil for Martian Exploration Mission
Authors: Harada Daiki , Takahashi Yusuke , Oshima Nobuyuki , Yamada Kazuhiko
Published: July 2018

In this research, aerodynamic characteristics of a closed-canopy-type parafoil for Martian exploration mission are numerically investigated at low Reynolds number region. Membrane deformation by internal pressure of a parafoil is simulated by using a virtual particle method. The computational results show that aerodynamic characteristics are affected by membrane deformation and difference of a shape of arch. Membrane deformation decreases pressure on the lower surface of a parafoil, and a large central angle of an arch increases pressure on the upper surface. Because of these effects, parafoil model with a large central angle of an arch and membrane deformation has lower lift-drag ratio.
Development of Removal Technology Using Ozone Microbubble With a Venturi Tube
Authors: Arai Yoshihiro , Abe Yutaka , Kaneko Akiko , Kanagawa Tetsuya , Fujimori Ken , Ike Masatoshi
Published: July 2018

The removal technology of single-wafer processing using ozone is proposed on photoresist stripping in the semiconductor manufacturing in order not to generate residual sulfate group after stripping. It is revealed that Disk-shaped nozzle proposed by the authors forms a vortex structure between the disks which is considered to cause the reduction of photoresist stripping rate. This study proposes a disk-shaped convex nozzle. In order to investigate the effects on the flow caused by the presence or absence of the convex, visualization using a high-speed video-camera and numerical simulation of the flow between the disks were conducted. Also, the stripping experiments were conducted to investigate the effects on the photoresist stripping rate caused by the presence or absence of the convex. As a result, the vortex structure that was observed in the disk-shaped nozzle has been disappeared in the disk-shaped convex nozzle. In addition, it is revealed that disk-shaped convex nozzle has the higher stripping ability than disk-shaped nozzle in the convex part. Next, as a stripping method that is different from the conventional, we suggest the ozone microbubble with a venturi tube. To obtaining knowledge about the performance of the photoresist stripping with the ozone microbubbles, first, the generation of ozone microbubbles is observed in the venturi tube via a high speed video camera. Next, to clarify the effect of the superficial liquid and gas velocities on the ozone water concentration and the photoresist stripping rate, ozone water concentration measurement and photoresist stripping experiments were conducted. As a result, the ozone water concentration with increasing superficial velocity increase and the remaining photoresist thickness reduce. In addition, compared with the existing study, it is suggested that the superficial liquid and gas velocities and ozone water concentration affect the photoresist stripping rate.
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.
Preliminary Investigation on Convective Heat Transfer of Rod Bundle Flow With Spacer Grid for Nuclear Fuel Assembly Application
Authors: Lee Chi Young , Shin Chang Hwan , In Wang Kee , Oh Dong Seok , Chun Tae Hyun
Published: July 2018

The convective heat transfer of rod bundle flow with spacer grid was investigated preliminarily for nuclear reactor core application. As the test fluid, the water was used. To simulate the nuclear fuel assembly, 4×4 rod bundle with P/D (=pitch between rods/rod diameter) of ∼1.35 was prepared together with a spacer grid with twist-mixing vane. A single heated section with five thermocouples embedded in the surface along the circumferential direction was installed around the center subchannel. The measurements of wall temperatures were carried out upstream and downstream of spacer grid. For the rod bundle flow at the inlet of spacer grid (i.e., upstream of spacer grid), the wall temperatures at the gap and subchannel centers exhibited the higher and lower, respectively, which was because in the subchannel center, the axial flow velocity became higher, as compared with the gap center. On the other hand, downstream of spacer grid, the rod wall toward the tip of twist-mixing vane showed the lowest temperature in the measurements along the circumferential direction of rod wall. Near the twist-mixing vane, the averaged wall temperature was observed to be remarkably low, which implies that the twist-mixing vane is an effective tool to enhance the convective heat transfer performance. However, along the axial flow direction behind the spacer grid, the averaged wall temperatures became to increase, and the enhancement of convective heat transfer performance by mixing vane faded away.
Effects of Contraction Ratio on Elastic Instability of Hyaluronate Solution in a Micro Channel
Authors: Oka Taiki , Hidema Ruri , Suzuki Hiroshi , Komoda Yoshiyuki
Published: July 2018

Flow behaviors of sodium hyaluronate (HA-Na) in water solution and in phosphate buffered saline (PBS) solution as a viscoelastic fluids in planer abrupt contraction-expansion channels has been observed in this study. Especially, the effect of the geometry of the flow path on the flow behavior was focused on. The corner vortices in the corner of the upper region in the abrupt contraction-expansion channels were also analyzed to quantify the flow characteristics. The elasticity numbers of the solution, which is affected by rheological properties of the solution and the channel geometry had a big influence on the fluidity, that is, stable or unstable, when the concentration of the solution in lower. It was concluded that such stable and unstable flows are categorized on Wissenberg-Reynolds number space.
Ultra-High Frequency Sound Waves for Microparticle Separation
Authors: Destgeer Ghulam , Alazzam Anas , Sung Hyung Jin
Published: July 2018

In this study, we have demonstrated a particle separation device taking advantage of the ultra-high frequency sound waves. The sound waves, in the form of surface acoustic waves, are produced by an acoustofluidic platform build on top of a piezoelectric substrate bonded to a microfluidic channel. The particles’ mixture, pumped through the microchannel, is focused using a sheath fluid. A travelling surface acoustic wave (TSAW), propagating normal to the flow, interacts with the particles and deflect them from their original path to induce size-based separation in a continuous flow. We initially started the experiment with 40 MHz TSAWs for deflecting 10 μm diameter polystyrene particles but failed. However, larger diameter particles (∼ 30 μm) were successfully deflected from their streamlines and separated from the smaller particles (∼ 10 μm) using TSAWs with 40 MHz frequency. The separation of smaller diameter particles (3, 5 and 7 μm) was also achieved using an order of magnitude higher-frequency (∼ 133 MHz) TSAWs.
Measurement of Three-Dimensional Particle Distribution by Tomographic Digital Holography
Authors: Tani Shunsuke , Tanaka Yohsuke , Murata Shigeru
Published: July 2018

This paper presents a measurement of three-dimensional particle distribution by tomographic digital holography. Holographic patterns of particles (particle Reynolds number Rep=0.79, average diameter dp=73.5 μm) settling in a static flow were recorded by two high speed cameras orthogonal to each other. Cameras were calibrated by a proposed method using a calibration device and a pattern matching. The calibration accuracy of the method is within 0.34 times of particle diameter.
Measurement Technique for Unsteady Low-Speed Flow Fields Using Poly(TMSP)-Based Pressure Sensitive Paint
Authors: Mori Hideo , Maeda Kyohei , Furukawa Masato , Akiyoshi Masao
Published: July 2018

Nonstationary analysis of flow field is required to detect the source of aerodynamic noise, in order to accomplish the reduction of aerodynamic noise in life environment, including low-frequency noise, which may be harmful for human health. Pressure sensitive paint (PSP) is a quantitative pressure visualization technique on solid surfaces based on oxygen quenching of luminescent molecule. Polymer-type PSP composed of PtTFPP, a luminescent molecule with high oxygen quenching probability, and poly(TMSP), a glassy polymer with high oxygen permeability, has high pressure sensitivity for low-speed flow field. However, the pressure sensitivity of the polymer-type PSP for nonstationary pressure change has not been examined enough. In this study, we investigate the time response of the poly(TMSP)-based PSP, to evaluate the feasibility of the polymer-type PSP as a measurement tool for nonstationary low-speed flows, when the frequency of pressure fluctuation is relatively low. Because response time of polymer-type PSP is proportional to the square of the thickness of the PSP layer, we prepare thinner-layer PSP to increase the response speed by reducing the amount of polymer. The polymer-type PSP is applied to measurement of nonstationary pressure distribution around a circular cylinder in low-speed flow, and compare the amplitude spectra of PSP and that of pressure probe, which are obtained by FFT analysis. As a result it is clarified that the sensitivity of the PSP for pressure variation lower than 100Hz is as high as that for stationary pressure. For pressure variation higher than 100Hz the sensitivity decreases as the frequency of pressure variation increases, but pressure variation with the amplitude of about 300Pa can be detected by the poly(TMSP)-based PSP even if the frequency is as high as 850Hz. Furthermore we have visualized the distribution of the integrated intensity of the PSP amplitude spectrum around the peak, to visualize the area with large pressure variation on the cylinder surface.
Characteristics of Fresh Water Permeation in Hollow Fiber Membrane Module for Pressure Retarded Osmosis
Authors: Terashima Shingo , Hayashi Hidechito , Okumura Tetsuya , Matsuyama Kei , Ueyama Tetsuro , Sakai Hideyuki
Published: July 2018

Forward Osmosis (FO) is recently paied attention to preprocessing of the Reverse Osmosis (RO). It can reduce the input power of RO plant. It is required to reduce the salt concentration at outlet and increase the permeation flow rate. In this paper, the characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in FO system. It is cleared that the disappearance of fresh water and the concentration polarization in hollow fiber largely influence to the reduction of permeation flow rate in the case of the low fresh water flow rate. Concentration of fresh water and the leakage of salt influence to the reduction of permeation flow rate in the case of high fresh water flow rate.
Geometrical Effects on Fluid Mixing of Pulsatile Flow in Convergent-Divergent Micromixer
Authors: Afzal Arshad , Kim Kwang-Yong
Published: July 2018

Time-dependent pulsatile flows have been used by many researchers for fast and efficient mixing at micro-scale [1–2]. In a recent study, a convergent-divergent microchannel with sinusoidal walls showed a strong coupling with pulsatile flow for enhanced mixing performance over a short mixing length [3]. In the present study, effects of two geometrical parameters, i.e., the ratio of amplitude to wavelength and ratio of throat-width to depth on mixing performance, were analyzed with the Strouhal number and the ratio of pulsing amplitude to steady flow velocity at a fixed Reynolds number, Re = 0.5. The flow and mixing analyses were performed using unsteady Navier-Stokes equations and a diffusion-convection model for species concentration.
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.
DNS of Heat Transfer Reduction in Viscoelastic Turbulent Channel Flows
Authors: Kim Kyoungyoun , Sureshkumar Radhakrishna
Published: July 2018

A direct numerical simulation (DNS) of viscoelastic turbulent channel flow with the FENE-P model was carried out to investigate turbulent heat transfer mechanism of polymer drag-reduced flows. The configuration was a fully-developed turbulent channel flow with uniform heat flux imposed on both walls. The temperature was considered as a passive scalar. The Reynolds number based on the friction velocity (uτ) and channel half height (δ) is 125 and Prandtl number is 5. Consistently with the previous experimental observations, the present DNS results show that the heat-transfer coefficient was reduced at a rate faster than the accompanying drag reduction rate. Statistical quantities such as root-mean-square temperature fluctuations and turbulent heat fluxes were obtained and compared with those of a Newtonian fluid flow. Budget terms of the turbulent heat fluxes were also presented.
Wind Tunnel Experiment and CFD Simulation for Multiple Wind Turbine Arrangements
Authors: Park Jong-Jin , Kim Dong-Hyun , Tran Thanh-Toan , Oh Min-Woo , Shin Yo-Seph
Published: July 2018

This paper experimentally and numerically investigates the interference effects of the multiple arrangements of horizontal-axis wind turbines. The 1:86 scale blades of the NREL 5-MW baseline wind turbine model is accurately constructed using a 3D printer. Its torque and power are directly measured by a designed dynamometer system installed in the experimental nacelle base. The total numbers of 2 and 3 turbines are longitudinally arranged and tested for different downwind distances up to 10D (D is the rotor diameter). Some of the test cases are also modeled and analyzed using three-dimensional unsteady computational fluid dynamics (CFD), and then compared with our experimental tests. The results for the downwind interference effect on multiple wind turbine arrangements are practically presented and investigated in this study.
Multidimensional Measurements of Turbulent Boundary Layer Including Scattered Particles Using PIV Technique
Authors: Sugawara Yoshiki , Tsukahara Takahiro , Kawaguchi Yasuo
Published: July 2018

Although many experimental researches on solid-gas flows have been conducted, the involved stress balance problem has not been elucidated. To have a deep investigation of the stress balance in gas flow with entrained solid particles, this study conducts particle image velocimetry (PIV) experiment on a horizontal turbulent boundary layer. In the experiment, air and micro-scale glass beads are chosen as the gas phase and solid particles, respectively. The velocities of both air and solid particles are obtained simultaneously based on the acquired images and by image processing; each term of the stress balance equation is calculated and the influences of solid particles are analyzed. Based on the experiment results, the dominant term of the stress in the solid-gas flow as well as the influence of the solid particles on the stress distributions are identified.
A Numerical Model for the Motion of Large Non-Spherical Object in Fluidized Bed
Authors: Higashida Kyohei , Yamada Teppei , Tsuji Takuya , Tanaka Toshitsugu
Published: July 2018

In practical application of fluidized beds, large solids coexist with small solids. Tsuji et al. (AIChE J., 60(5), pp. 1606–1620, 2014) proposed a numerical model which expresses the behavior of flows including dense solid objects with large size difference based on the DEM-CFD coupling method. In the present study, the model is extended to represent the non-sphericity of large objects by adding a multi-sphere model. Firstly, we perform validation study in a mm-size bubbling fluidized bed and confirm qualitative agreements between the numerical model and the experiment. After that, sinking and floating motion of a large non-spherical object in a fluidized bed are numerically investigated in detail.
Consideration of Sub-Surface Vortices in Suction Sump Using LES
Authors: Tomimatsu Shigeyuki , Yamade Yoshinobu , Zhang Huilai
Published: July 2018

In this study, sub-surface vortices generated in a suction sump are simulated. In an experimental model test, sub-surface vortices are qualitatively observed under a bell mouth. Vortex core lines corresponding approximately to sub-surface vortices are visualized when a fine mesh model is used. On the other hand, it is impossible to visualize the vortex core line when a coarse mesh model is used. Therefore, it is obvious that analytical accuracy is improved by using the fine mesh model. However, it is also obvious that a longer total simulation run time is necessary when using the fine mesh model; a significant problem for practical engineers. In this paper, the effects of mesh models are mainly investigated using coarse and fine mesh models. The fine mesh model is generated by refining the coarse mesh model and indicates that a high performance computing technique is an effective approach for suction sump simulation.
Flow Instability in Off Design Condition of Vaned and Vaneless Diffuser Centrifugal Pump
Authors: Hiramatsu Hideto , Shibata Akiha , Komaki Shutaro , Miyagawa Kazuyoshi , Sano Takeshi
Published: July 2018

In this study, the performance and the internal flow of one stage model centrifugal pump with both vaned and vaneless diffuser were investigated. To measure the internal flow of the diffuser and the impeller easily, air was used in this pump test. As a result of measuring pressure fluctuation, the rotating stall was observed in the vaned and vaneless diffuser. We clarified the generating mechanism and characteristics of the rotating stall in the diffuser and the difference between the unsteady flow fields in both diffusers. In case of the vaned diffuser, the number of rotating stall cells were 4 in the diffuser and the cell propagation speed ratio was about 5 percent of the impeller rotating speed. On the other hand, in case of the vaneless diffuser, the cell number was 2, and the propagation speed ratio was about 10 percent of that. These phenomena in both diffuser pumps were simulated by unsteady 2D and 3D CFD computations. By using these computations, the vortex at the trailing edge of the diffuser vanes blocked the flow and induced separate flow at the leading edge resulted in the rotating stall. This research indicated that these vortices induced the total pressure loss increasing. Also, the rotating stall was found not only in the diffuser but also in the impeller by the flow simulation of the vaneless diffuser. And it was confirmed that the vortices at the impeller trailing edge and leading edge in the stall cells cause the total pressure loss.
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.
Blockage and Distortion Effects on a Vane Island Type Diffuser Performance of Centrifugal Pumps for Various Flow Rates
Authors: Si Qiaorui , Dazin Antoine , Dupont Patrick , Roussette Olivier , Bois Gérard
Published: July 2018

Experimental investigation of mean flow velocity and pressure inside the vane-island type diffuser passage of a laboratory centrifugal pump model is presented in this paper. A three-hole directional probe was used to investigate hub to shroud flow properties at diffuser leading and trailing edge planes and at the mid-section between suction and pressure sides along the diffuser passage. All these measurements have been performed for five different flow conditions. The flow structures at the inlet section of the diffuser and along with the passage were analyzed in detail, with a focus on the flow distribution and the pressure recovery evolution of different diffuser part. Block age and distortion effects are analyzed using existing published Particle Image Velocimetry (PIV)measurements in the outer part of the impeller and around the diffuser throat in order to get a better understanding of the overall performances and local flow structures of such a diffuser design.
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.
Large Eddy Simulation of Unsteady Vortices in a Pump Sump
Authors: Yamade Yoshinobu , Kato Chisachi , Nagahara Takahide , Matsui Jun
Published: July 2018

Unsteady vortices in the test pump sump with 100 mm height and 100 mm diameter of the inlet pipe are investigated by performing large eddy simulations (LES). Computational grids composed of 2 billion hexahedral elements with 0.255 mm resolution were used for the LES. These grids resolve the turbulent boundary layer that develops on the wall of approaching channel; however it is not enough fine to capture viscous core of the submerged and air-entrained vortices. In this study, we focused to analyze how and why submerged and air-entrained vortices were appeared and disappeared. By performing LES for a long time period (∼16 seconds), we successfully captured the unsteady events several times, including generations and disappearances of the submerged and air-entrained vortices. In this paper, the details of the appearances and disappearances of vortices will be shown.