bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical prediction of the blade trailing edge broadband noise of a plug fan
Authors: Zurbano-Fernández Ignacio , Guédel Alain , Robitu Mirela , Roger Michel 
Published: May 2021

Abstract
This study presents a low-order broadband noise prediction tool for centrifugal plug fans, based on analytical models using inputs from CFD simulations. Firstly, the fan used as a reference in this investigation was tested in a double reverberant room where the aerodynamic performance and the acoustic signature were measured simultaneously. Secondly, CFD RANS simulations of the fan in the test rig were performed. The outcome of the simulations is then used to feed Amiet’s analytical broadband noise model, along with wall-pressure spectral and correlation length models. Amiet’s model has been transposed to a rotating blade, adapted to the geometry of the fan. Finally, the model predictions are compared with the measurements.
Numerical Investigation of Pressure Fluctuation and Cavitation inside a Francis Turbine Draft Tube with Air Admission through a Fin
Authors: Zhang Ruizhi , Yu An , Nishi Michihiro , Luo Xianwu 
Published: May 2021

Abstract
The stabilizer installation and air admission have been proved to be two effective ways to alleviate the pressure fluctuation in the Francis turbine draft tube. In this research, a combined method of these two ways, i.e. air admission through a fin (one type of the stabilizer) is applied, and its effectiveness, especially air admission’s effects, on pressure fluctuation suppression has been investigated through numerical calculation. Two cases of different air amount (Q
*=0.01 and 0.02) are investigated. Results show that cavitation inside the draft tube is suppressed and the size of vortex rope is also slightly decreased after air is admitted. As a result, pressure fluctuation inside the draft tube is generally alleviated compared with no air admission case. The maximum amplitude of pressure fluctuation decreases by 9.2% with 0.01 air admission, and by 26.3% with 0.02 air admission. In addition, the position where the maximum amplitude of pressure fluctuation occurs also moves downstream, which should be due to the more violent interaction between the vortex rope in the main stream and a small vortex rope attached to the fin. Consequently, a slight increase of pressure fluctuation downstream the fin can be observed. Although air admission through the fin can suppress pressure fluctuation in the draft tube, it would also lead to turbine efficiency decrease. Therefore, the application of both fin and air admission should be carefully considered to achieve better performance for Francis turbines.
Numerical Investigation of Compressor Tandem Aerofoils Featuring Near-Endwall Modification
Authors: Eckel J , Gümmer V 
Published: May 2021

Abstract
A highly loaded 1.5-stage low-speed compressor stage is investigated numerically using fully turbulent and steady state RANS simulations. The tandem stator at the end of the stage is replaced by a tandem stator with a near-endwall modification. This unconventional compressor blade design is using a single profiling near both endwalls and a tandem profiling at midspan. Using this modification the positive behaviour of a tandem stator can be maintained. Locally the leading edge of the rear vane and as a result the gap flow near both endwalls will be removed by introducing a single-profile segment. This paper will describe the approach to set up a numerical model for the new geometry and will characterize the flow features and loss mechanisms of the near-endwall modification. The first comparison between the stators with and without near-endwall modification, showed a reduction of corner separation at the rear vane, caused by the removal of the low momentum gap-flow. On the other side, the near-endwall modification is creating higher losses at the connecting region between the tandem and single segment. The numerical results presented in this paper will be the starting point for further optimizations of the tandem blade with near-endwall modifications.
Design Concept with Tip Leakage Vortex Control for Centrifugal Compressor Flow Stabilization
Authors: Tomita Isao , Furukawa Masato 
Published: May 2021

Abstract
Centrifugal compressor applied to turbochargers is required to operate stably in wide range from choking to surging. In our past research, authors suggested a design policy called STB (flow Stabilization by inducing Tip leakage vortex Breakdown) concept, which indicates “Operating range can be enhanced with uniform blockage region generated by tip leakage vortex breakdown”. In this study, authors tried to validate the STB concept by redesigning a given impeller into a wide range compressor. In this research, detailed analyses showed that non-uniform and unstable stall occurred at small flow rate in the conventional impeller. On the other hand, in the redesigned new impeller having high inducer loading, unsteady numerical calculation showed that the strengthened blade tip leakage flow generated a circumferential uniform blockage region, which could stabilize its internal flow. As a result of performance test of the new impeller, considering that the surging flow rate at the same shaft speed was reduced by 3% and the pressure ratio at the surging point had been improved from 2.8 to 2.9, the surging flow rate at the pressure ratio of 2.8 could be reduced by 8%. In this way, it was found that the tip leakage flow was dominant with the stall phenomenon of the centrifugal compressor, and it was also confirmed that the STB concept was one of the effective means for the operation range enhancement.
Extensive Experimental and Analytical Investigation of the Aerodynamic Flow Field of Labyrinth Seals with Innovative Liner Configurations
Authors: Hühn Lisa , Wilhelm Julius , Schwitzke Corina , Bauer Hans-Jörg 
Published: May 2021

Abstract
The state-of-the-art sealing systems in aircraft engines are labyrinth seals to regulate mass flow between rotating components. To prevent structural damage of vital parts during a rubbing process, abradable liner configurations with hollow body structures are applied on the stator. Compared to smooth stator surfaces, these structures increase the cross-sectional area of the sealing gap and, thus, lead to a higher leakage. The aim of this paper is to identify the main geometrical parameters influencing the aerodynamic behavior of various liner configurations. As a basis of an analytical study, an extensive experimental database is required. For this purpose, a test rig is set up at the Institute of Thermal Turbomachinery (ITS). Three liner structures (honeycomb, rhombus, and polyhedral structures), two seal fin configurations, and the effect of the adjusted nominal clearances (0.1-1.0 mm) and different pressure conditions are investigated. The experimental results will be presented, discussed, and evaluated by means of established parameters. The focus is on the leakage of the seal, the discharge coefficient, and the equivalent gap width. Additionally, the influence of the geometric shape of the liner structures is discussed. Flow separation and flow direction play the main role. With the results of this paper, optimization guidelines are derived for the design of innovative liner configurations.
Supervised Learning for Generating Fair Curves with Curvature Boundary Conditions
Authors: Sudhof Samuel , Uemura Norimichi , Uchiumi Masaharu 
Published: May 2021

Abstract
Fairness measures are means to guess if a curve is suited for an aerodynamic application if no knowledge of the flow field is available. Fair curves are proposed as a means to reduce the number of parameters for generating a supersonic rotor blade. A specific new measure of fairness is proposed with the goal of being numerically less demanding to evaluate than previously known measures of fairness. Gradient search for an optimum of this fairness value is nevertheless computationally expensive. Therefore, a neural network was trained using Adamax optimization that can produce curves of acceptable quality instantly for applications where real time response is needed.
Optimization procedure to design a Francis turbine runner using 2D Through-flow analysis
Authors: Watanabe Ryo , Miyagawa Kazuyoshi , Khozaei Mohammad Hossein , Yamaguchi Naoki , Masuko Toshitake 
Published: May 2021

Abstract
Due to increasing usage of Feed-in Tariff (FIT), which is a subsidy system to encourage expansion of renewable energy and to reduce costs associated with introduction of renewable energy, demand for hydraulic turbine designers has increased solely for the purpose of improving turbine performance. With these requirements, CFD simulation is a powerful tool for designers to improve the internal flow and pressure distribution in turbines. Traditionally, most designers use a trial-and-error process based on previous experience to design new turbines. Usually, achieving the goal is a lengthy and painstaking process. This paper proposes a novel method which combines both CFD and optimization methods to automatically optimize a Francis turbine. This procedure includes four components: a design program, a CFD solver, a scheduler, and an optimization algorithm. This paper describes an attempt to automatically optimize a Francis turbine runner by using ANSYS Vista TF as the 2D CFD solver based on through-flow theory, and ANSYS CFX 19.1 as the 3D CFD solver based on Finite Volume Method (FVM). The runner geometry is parameterized by Bezier curves in the design program. CFD analysis is performed to assess the efficiency of the runner, and also the output power is calculated by runner torque. These two parameters are used as the objective function of the optimization algorithm. This method is used to optimize the runner geometry, which consists of two parts: the meridional plane and profile camber lines. We confirmed that the new turbine, which was optimized by the above-mentioned method, has better efficiency than the existing one.
Transient Characteristics of a Centrifugal Pump at Rapid Startup
Authors: Tanaka Teiichi , Toyomoto Takeshi , Nasu Kosuke , Tabaru Michiya 
Published: May 2021

Abstract
An experimental and CFD(Computational Fluid Dynamics) study was conducted on the transient behavior of a rapidly starting centrifugal pump. The transient characteristics of the centrifugal pump in the transient period were examined from experimental results. Instantaneous flow rate and pressure were measured at suction and discharge ports of the pump with rotational speed and pump shaft torque when the pump is in transient operation. The suction and discharge pressures of the pump were measured by pressure sensors of the strain gauge type. The unsteady flow rate was calculated based on the pressure difference between two pressure measurement points in the straight suction pipe of the pump. The unsteady pump rotational speed and shaft torque were measured using the highly responsive torque meter. The true pump total head because of the pumping action at the unsteady operation of the pump was able to be calculated by subtracting the apparent pump total head cause by the fluid inertia effect from the measured pump total head. According to the present study, the transient characteristics of the rapid starting pump can be measured using the experimental setup. And it was shown that the dynamic operating point and shaft torque during the pump startup period deviate from the quasi-steady change. Comparing the experimental results with CFD, the reason for the deviation of transient characteristics from quasi-steady change was considered to be due to that the formation of the flow field in the pump during the transient period is delayed relative to the flow field of the steady-state.
Evaluation of self-induced oscillation of the flow control valve by fluid structure interaction analysis
Authors: Fukao Shinji , Futahasji Kensuke , Umehara Ryuichi , Baba Takeo 
Published: May 2021

Abstract
In the flow control valve used in the upper or the lower stream of a turbomachinery, when opening is small, the self-induced oscillation resulting from a clearance gap flow may occur. In this study, the mechanism of self-induced oscillation which occurs on the small valve opening condition was examined. And a concept to control the self-induced oscillation was built. The air model test of the flow control valve was carried out, and it was confirmed that self-vibration occurs under specific conditions. Moreover, stability evaluation using CFD was carried out, and it checked that the calculation results become the almost same tendency as a test results. The area where the instability force is generated on a valve was grasped from the simulation results, and it checked that stability was changed with flow field differences. Based on these results, stabilization of the flow control valve was attained by improving clearance gap geometry of the valve sheet area. It checked that the intended flow field was obtained in the geometry in CFD analysis, and it confirmed that fluid additive damping became positive in CFD.
Characteristics of fluid exciting force due to blade row interaction of a propeller turbine
Authors: Mori Ryosuke. , Ajiro Kazushi. , Miyagawa Kazuyoshi. 
Published: May 2021

Abstract
As the use of renewable energy is promoted, much researches on propeller-type turbines are carried out. To improve reliability, it is important to evaluate the fluid exciting force due to blade row interaction that may cause vibration or fatigue fracture. In this paper, CFD(URANS) simulations and experimental studies were conducted to understand the characteristics of the fluid exciting force due to blade row interaction of a propeller turbine. To evaluate the fluid exciting force, strain gauges and pressure sensors were used in the closed-loop water channel. The fluid exciting force acting on the rotor due to the stator was measured by changing stator load type and the rotor-stator distance. Based on the difference in the attenuation tendency of potential interaction and wake interaction due to changes in the rotor-stator distance, the influences of these interactions could be distinguished. As results of experiments and computation, wake interaction affecting pressure fluctuation was hardly attenuated due to the swirling flow and changing the rotor-stator distance has little effect on the attenuation of blade row interaction.
On the stability of boundary-layer flow over a rotating cone using new solution methods
Authors: Hussain Zahir , Garrett Stephen J. 
Published: May 2021

Abstract
In this study, a new solution is applied to the model problem of boundary-layer flow over a rotating cone in still fluid. The mean flow field is perturbed leading to disturbance equations that are solved via a more accurate spectral numerical method involving Chebyshev polynomials, both of which are compared with previous numerical and analytical approaches. Importantly, favourable comparisons are yielded with existing experiments [17] and theoretical investigations [6] in the literature. Meanwhile, further details will be provided of potential comparisons with new experiments currently in the pipeline.
Physically, the problem represents a model of airflow over rotating machinery components at the leading edge of a turbofan. In such applications, laminar-turbulent transition within the boundary layer can lead to significant increases in drag, resulting in negative implications for fuel efficiency, energy consumption and noise generation. Consequently, delaying transition to turbulent flow is seen as beneficial, and controlling the primary instability may be one route to achieving this. Ultimately, control of the input parameters of such a problem may lead to future design modifications and potential cost savings.
Our results are discussed in terms of existing experimental data and previous stability analyses on related bodies. Importantly, broad-angled rotating cones are susceptible to a crossflow instability [6], visualised in terms of co-rotating spiral vortices, whereas slender rotating cones have transition characteristics governed by a centrifugal instability [9], which is visualised by the appearance of counter-rotating Görtler vortices. We investigate both parameter regimes in this study and comment on the accuracy of the new solution method compared with previous methods of solving the stability equations.
Improvement of compact Darrieus-type hydraulic turbine for extra low head by changing inlet shape
Authors: Kikugawa H , Kawano Y , Shuto M , Furukawa A 
Published: May 2021

Abstract
Hydraulic power generation has a potential as an environmental friendly energy, which is not discharging a carbon dioxide gas during operation. Currently, high and middle water head turbine has been fully developed in practical use. However, extra low head hydraulic turbine has not been developed yet as a commercial utilization. Compact Darrieus-type hydraulic turbine has been focused on for small waterway. The purpose of this study is to improve the performance of the compact Darrieus-type hydraulic turbine, by changing inlet shape. In our previous study, the blade shape, the number of blades, the water wheel diameter ratio of chord length and pitch circle radius are optimized. The purpose of the present study is to further improve the performance of the compact Darrieus-type water turbine based on former results. In this study, the inlet shapes were changed to increase inflow velocity and to contribute improvement of efficiency. As a result, the efficiency of the turbine with using only half side counterpart nozzle was increased compared to the other settings.
Numerical calculation of the rotordynamic coefficients of a LOX-Turbopump Seal for the LUMEN LOX/LNG demonstrator rocket engine
Authors: Müller Max Axel , Traudt Tobias , Schlechtriem Stefan 
Published: May 2021

Abstract
In rocket engines seals are one of the key elements for a successful turbopump operation. They are not only responsible for reducing the leakage but they also have a huge influence on the rotordynamic behaviour. Depending on the design, the seal on a turbopump impeller can damp or excite rotordynamic instabilities. In this work we present transient 3D CFD simulations of straight gap seals, which are used to determine the rotordynamic coefficients. After that the numerical simulation is extended to characterize the influence of the impeller to housing clearance and swirl brakes on the rotor dynamic coefficients. We show that the inertia term cannot be neglected for the investigated nominal rotational speed of the rotor and high absolute whirl frequency ratios especially for the rotor housing clearance. Finally the coefficients calculated by numerical simulation are used in the equations of motion for a floating ring seal and the equations are solved numerically to do a sensitivity study of a floating ring to variations in axial force, rotor displacement and floating ring mass.
Influence of Rotational Speed of an Inducer on the Propagation Velocity of Super-synchronous Rotating Cavitation
Authors: Kondo Sota , Kanamaru Moena , Kawasaki Satoshi , Iga Yuka 
Published: May 2021

Abstract
The phenomenon that a cavity rotates faster than the rotational speed of the pump in the direction of rotation is called super-synchronous rotating cavitation (super-S RC). It is known that super-S RC is often observed in rocket turbopumps, but that it is rare to be observed in industrial pumps. Therefore, we form a hypothesis that its occurrence is related to the rotational speed of pumps. In this study, experiments of an inducer were conducted at four rotational speed at Kakuda Space Center in the Japan Aerospace Exploration Agency. The pressure fluctuation and the rotor vibration were measured, and the propagation velocity ratio of super-S RC and the frequency of unsteady cavitation in the super–S RC were determined at each rotational speed. As a result, when the cavitation number is the same, the propagation velocity ratio is almost the same regardless of the rotational speed of the inducer. It means that the faster the rotational speed, the faster the unsteady cavitation oscillates in the inducer despite the condition of the same cavitation number. It indicates that rotating cavitation does not occur under a certain rotational speed because of the limitation of the frequency of unsteady cavitation, which is known in hydrofoil.
A Straight-Bladed Vertical-Axis Turbine for Wave Energy Conversion: Effect of Guide-Vane Geometry on Performance
Authors: Hayamizu Y , Kitano K , Suzuki T , Morita S , Ohtsuka S , Takao M , Kinoue Y , Setoguchi T 
Published: May 2021

Abstract
This study proposes a straight-bladed vertical-axis turbine for ocean-wave energy conversion. The aim is to develop a novel air turbine suitable for an oscillating water column in a wave energy plant. To this end, the performances of straight-bladed vertical-axis turbines were investigated for different guide-vane geometries in a wind tunnel experiment. The rotor has four straight blades with an NACA0018 profile, a chord length of 80.5 mm, a pitch diameter of 460 mm, and a blade width of 490 mm. In this study, the guide-vane geometry was varied as arc, semi-arc, and semi-arc with a straight part. Under steady flow conditions, the turbine performance was evaluated by determining the torque, input and flow coefficients, and the turbine efficiency. The semi-arc blade geometry decreased the input coefficient and increased the torque coefficient. Moreover, the semi-arc blade with a straight part improved the starting characteristics of the turbine and its efficiency over a wide range of flow coefficients.
Fundamental Study on Improvement of Performance of Wells Turbine Blade
Authors: Isatake Naoya , Yamanouchi Kousuke , Hamakawa Hiromitsu , Kurihara Eru , Hayashi Hidechito 
Published: May 2021

Abstract
In the present paper the attention is focused on the effect of the dimples on the stall characteristics and aerodynamic sound radiated from two-dimensional airfoil. In general, two-dimensional blade is used as the airfoil of Wells turbine. We measured the lift force acted on the airfoil and aerodynamic sound. The dimples were effective to improve the stall characteristics. As the dimple diameter and number of dimples increased, the broadband noise at higher frequency component increased slightly compared with normal airfoil. The dimples were not effective to reduce the broadband noise radiated from airfoil. In contrast, the dimples were effective to reduce the discrete tone noise radiated from airfoil. This noise depended on the geometry, position and number of dimples. The suitable geometry, position and number of dimples were discussed to improve the stall characteristics and reduction of aerodynamic sound.
Particle Behavior in Curved Microchannels: Aspect Ratio Effects
Authors: Hayamizu Y , Nakamura A , Hyakutake T , Gonda T , Morita S , Ohtsuka S , Yanase S 
Published: May 2021

Abstract
The sorting devices of microfluidic systems operate by both passive and active mechanisms. The microchannels of these systems are often curved to cope with secondary flows, which allow sorting or mixing. Therefore, it is essential to characterize the secondary flows in microfluidic systems. In this study, we investigate the particle behavior in a spiral rectangular microchannel and clarify the effects of the aspect ratio and Dean number De on particle sorting by comparing experimental and numerical results. We fabricated Archimedean spiral microchannel models with the rectangular cross-section of millimeter-scale dimensions. Particle sorting in the microchannels was observed by the particle-tracking velocimetry (PTV) method. In addition, the particle-sorting mechanism was analyzed by the particle-tracking method in three-dimensional numerical simulations. When particle density exceeded water density, good sorting was observed when 20 < De < 40. The numerical particle-sorting behaviors agreed well with the experimental results.