Rotor Zone Research Articles

PROPULSION THRUST FORCE CALCULATION WITH CAVITATION FOR AN UNDERWATER VEHICLE

This paper aimed to evaluate the thrust force for a propeller taking into account cavitations, to analyze the dynamic and nautical characteristics of an ROV (Remotely Operated Vehicles). This approach is not a theoretical one, it also has a practical purpose to achieve high-performance propulsion systems with the lowest possible design costs. This is the purpose for which we want to create a viable and high-performance simulation model which allows optimization by numerical analysis, and in the end to make the prototype and perform measurements. The simulation is done in Ansys CFX and uses a 3D model for the propeller and duct of the T100 thruster produced by Blue Robotics. The simulation introduces the cavitation model from Ansys CFX, simplified Rayleigh-Plesset formulation, and we will perform analyses whit important improvements. Taking into account the results obtained in previous author work [1] and information from other scientifical papers, we will test fine discretization mesh in rotor zone to solve the cavitation. Increased resolution for the numerical scheme, two-order schemes for pressure momentum, and turbulence equations. Replacement of k-epsilon turbulence model whit a more performant k-omega model. The obtained results will be analyzed and compared with the experimental measurements.

Current Optimization Control of Switched Reluctance Motor for Low Speed Range

In this paper, two different strategies are combined to optimize the phase current control for switched reluctance motor (SRM). Firstly, considering the sampling and computation delay, a current prediction chopping control method is proposed to alleviate the current ripple during the entire excitation phase chopping process. Secondly, in order to cut down the large current ripple in the initial stage of phase current establishment and the excessive output current of the battery, a partitioned current control method is proposed to control the phase current with different control logic at different rotor zones. Finally, the two control strategies are combined to further optimize the phase current. In order to verify the proposed combined control strategy, a three-phase 12/8 poles SRM simulation model and experimental platform are built. The simulations and experiments are carried out to verify the effectiveness of the proposed control strategy.

Experimental Study of the Effects of Welding Depth and Heat Treatment on Residual Stresses in a Cracked Rotor

One of the important issues in power plants is the occurrence of cracks on the steam turbine rotor. Removing cracks by machining is a common repair method to prevent crack propagation and failure. However, excess machining and reducing the rotor radius is limited. Therefore, welding the machined zone is a good way to repair the rotor. In this paper, the effects of welding depth and heat treatment on residual stresses of a laboratory sample of a welded power plant rotor have been investigated. For this purpose, a minimized model of the turbine rotor made of VCN200 with two V-shaped grooves has been prepared and then the grooves have been, respectively, filled by 7- and 32-pass welding after preheating. Afterward, residual stresses in different rotor zones (welded and non-welded zones), before and after stress relieving heat treatment, have been measured by the hole drilling method. Results showed the presence of residual stresses in all areas of the rotor before heat treatment, i.e., tensile residual stresses in non-welded and 7-pass welded areas and compressive residual stresses in 32-pass welded area. The results also showed stress relieving heat treatment led to a significant reduction in residual stresses in all studied areas.

Performance analysis of a savonius vertical axis wind turbine integrated with wind accelerating and guiding rotor house

Though Micro Wind Technology has several advantages but its expansion is very slow due to few significant limitations such as low efficiency of wind turbines and public concerns regarding safety in the turbine vicinity, noise and visual impact. To overcome the limitations of micro wind technology, a Rotor House (RH) for vertical axis wind turbine has been proposed in the literature. It has been claimed that the RH utilizes free stream wind parcel of the area nearly double than the swept area of rotor and amplify velocity magnitude in the rotor zone up to 1.52 times the value of free stream velocity. In the present study contribution of proposed RH in terms of increase in the performance of micro vertical axis wind turbine has been investigated experimentally. In this regard a conventional three bladed savonius rotor model and RH model with optimized design is manufactured and tested under laboratory conditions as well as in open air conditions (field testing). By creating venture effect, the RH accelerates wind flow in the rotor zone and concentrates the flow on the effective location of rotor blade located inside the structure. RH contributes to improve the power coefficient of rotor from 0.125 to 0.218.

Application of Richardson extrapolation method to the CFD simulation of vertical-axis wind turbines and analysis of the flow field

There is still discrepancy regarding the verification of CFD U-RANS simulations of vertical-axis wind turbines (VAWTs). In this work, the applicability of the Richardson extrapolation method to assess mesh convergence is studied for several points in the power curve of a VAWT. A 2D domain of the rotor is simulated with three different meshes, monitoring the turbine power coefficient as the convergence parameter. This method proves to be a straightforward procedure to assess convergence of VAWT simulations. Guidelines regarding the required mesh and temporal discretization levels are provided. Once the simulations are validated, the flow field at three characteristic tip-speed ratio values (2.5 - low, 4 - nominal and 5 - high) is analyzed, studying pressure, velocity, turbulent kinetic energy and vorticity fields. The results have revealed two main vortex shedding mechanisms, blade- and rotor-related. Vortex convection develops differently depending on the rotor zone (upwind, downwind, windward or leeward). Finally, insight into the loss of performance at off-design conditions is provided. Vortex shedding phenomena at the low tip-speed ratio explains the loss of performance of the turbine, whereas at the high tip-speed ratio, this performance loss may be ascribed to viscous effects and the rapid interaction between successive blade passings.

Performance of SB-VAWT using a modified double multiple streamtube model

The present study introduces a new relation to evaluate the equilibrium induced air velocity in the mid plane between the upstream and downstream rotor zones to give a good improvement in prediction of the maximum power coefficient. The relation is derived as a function of both interference factor in upwind and downwind rotor zones determined using classical DMST model. The root-finding algorithm is used to obtain the interference factor both in upwind and downwind zones of the turbine at each streamtube. The comparison between the numerical results and the experimental data of 5-m, 17-m, and 34-m Darrieus VAWTs shows that the use of the introduced relation gives a sensible improvement in the prediction of maximum value for turbine power coefficient. A theoretical study is presented based on the use of well documented symmetrical NACA0012 turbine blade profile. The effect of wind speed and rotor solidity on maximum power coefficient and corresponding optimal speed ratio on the turbine rotor is evaluated in order to determine an improved aerodynamic configuration for a given application.

ATMOSPHERIC DISTURBANCES IN THE AIRFLOW AROUND MOUNTAINS AND THE PROBLEM OF FLIGHT SAFETY IN THE MOUNTAINS OF THE REPUBLIC OF ADYGEYA

This article considers airflow around mountain systems as a meso-scale atmospheric phenomenon. It presents a non-linear stationary dimensional theoretical model of the airflow of the North-West Caucasus Mountains, taking into account characteristics of a real mountain terrain. The article further discusses the results of the calculations of the speed field of the airflow and general regularities of the origin and the scale of the rotary-wave deformation of the airflow over the mountains. The calculation results have shown that for the model scenario I at wind speed U=15 m/s the disturbances are the most intense over the ridge crests, where they are characterized by the zone with rotors. The total length of the rotor zone downwind is more than the length of its nucleus and is close enough in value to the extent of the lee part of the terrain (downwind from the main top). The area of maximum amplitudes is located in the windward side of the rotor zone. These amplitudes are several times higher than the maximum height of the mountains. For the model scenario II (U=19 m/s) wave disturbances slightly increased in length downwind, but minimally changed in amplitude. The rotary zone changed and moved downstream. The model scenario III (U=22 m/s) is accompanied by sharp transformation of the rotor zone. Closed vortices disappear; there is no purely vertical and backward motion. The flow over the mountain greatly smoothed, and the rotor area completely disappeared. Flight safety indicators over the mountains of the Republic of Adygeya for two types of aircrafts (light-engine and speed) were calculated on the basis of the obtained data. In certain conditions, flights for both high-speed and single-engine aircrafts can be considered dangerous

Calculation and analysis of complex fluid flow and thermal fields in a fully air-cooled hydrogenerator

Fully air-cooled hydrogenerators are applied widely in power stations because of advantages such as high efficiency, simple structure, and easy maintenance. This study investigated fully air-cooled hydrogenerators, and a three-dimensional fluid and thermal coupling analysis model of a hydrogenerator was proposed. Using the finite volume method, the changes in complex fluid velocity in the stator and rotor zones at different times were determined. Additionally, temperature changes in metal parts and insulation in the hydrogenerator were investigated with respect to time from the start to steady state operation of a hydrogenerator. In the study, the time required for the temperatures of different hydrogenerator parts to reach a steady state was predicted. Following the starting of the hydrogenerator, the temperature distribution of different parts at the same time and the changes in the temperature distribution of parts at different times were determined in the hydrogenerator. The surface heat-transfer coefficient distribution law on the surfaces of rotor exciting winding was studied. The calculated temperature result was compared with the measured value, and the results indicated that the calculated value of temperature agreed well with the measured value. Thus, the study indicated the feasibility of designing a fully air-cooled hydrogenerator from a thermal analysis viewpoint.

Wave-Induced Boundary Layer Separation in the Lee of the Medicine Bow Mountains. Part I: Observations*

Abstract Two cases of mountain waves, rotors, and the associated turbulence in the lee of the Medicine Bow Mountains in southeastern Wyoming are investigated in a two-part study using aircraft observations and numerical simulations. In Part I, observations from in situ instruments and high-resolution cloud radar on board the University of Wyoming King Air aircraft are presented and analyzed. Measurements from the radar compose the first direct observations of wave-induced boundary layer separation. The data from these two events show some striking similarities but also significant differences. In both cases, rotors were observed; yet one looks like a classical lee-wave rotor, while the other resembles an atmospheric hydraulic jump with midtropospheric gravity wave breaking aloft. High-resolution (30 × 30 m2) dual-Doppler syntheses of the two-dimensional velocity fields in the vertical plane beneath the aircraft reveal the boundary layer separation, the scale and structure of the attendant rotors, and downslope windstorms. In the stronger of the two events, near-surface winds upwind of the boundary layer separation reached 35 m s−1, and vertical winds were in excess of 10 m s−1. Moderate to strong turbulence was observed within and downstream of these regions. In both cases, the rotor extended horizontally 5–10 km and vertically 2–2.5 km. Horizontal vorticity within the rotor zone reached 0.2 s−1. Several subrotors from 500 to 1000 m in diameter were identified inside the main rotor in one of the cases. Part II presents a modeling study and investigates the kinematic structure and the dynamic evolution of these two events.

Numerical prediction of pressure pulsation for a low head bidirectional tidal bulb turbine

The present paper aims to find out the relationship between pressure pulsations and operation mode, water head for a low head bidirectional tidal bulb turbine. 3D unsteady numerical simulations were performed and the accuracy of the method can meet the requirements of practical applications by comparing calculated results with the experimental data. The simulation results indicate that for a low head tidal bulb, runner rotational frequency (fn) is the major component of the pressure pulsations both in vaneless space or rotor zone. The intensity of this dominant frequency is influenced by gravity effect or secondary flow, which depends on the specific operation mode and location. In the rotational zone from guide vanes to blades, the flow is largely affected by gravity effect not water head, which result in the amplitudes with dominant frequency increase with rotational radius in ebb and flood modes. On the contrary, in the rotational zone from blades to diffusion tube, there is obvious secondary flow. Therefore, the amplitudes with dominant frequency is ruled by head change instead of gravity effect in ebb and flood modes.

Droplet characteristics and behaviors in a high-speed disperser

In order to intensify the gas absorption process, a high-speed disperser with a rotor 219mm in external diameter was designed to disperse the continuous liquid into droplets. The effects of rotational speed, radial distance, and inlet flow rate on droplet size and velocity were measured by using a high-speed camera in the air-water system. Results showed that the mean droplet diameter decreased with increasing rotational speed and decreasing radial distance or inlet flow rate. On the other hand, the droplet resultant velocity increased with increasing rotational speed or decreasing radial distance, but was hardly affected by the inlet flow rate. The Rosin–Rammler (R–R) distribution and three-parameter volume-based maximum entropy formalism (MEF) appropriately represented the droplet size distribution. Models for droplet motion in the rotor and cavity zones were successfully established to calculate the droplet velocity. The commercial code Fluent was adopted to simulate droplet characteristics and behaviors. The volume of fluid (VOF) model and the Euler–Euler multiphase model were implemented to predict the droplet size and velocity fields for gas and liquid, respectively. A comparison of simulated and experimental results indicated that the VOF model predicted the droplet size reasonably well, and the Euler–Euler multiphase model provided good estimates of the droplet velocity.

PIV experimental study on the flow field in the rotor zone of an annular centrifugal contactor

In this study, particle image velocimetry (PIV) technique was employed to measure the flow field in the rotor zone of an annular centrifugal contactor (ACC). The velocity distribution and streamline diagrams of the flow field relative to the stationary reference and rotating reference frame was investigated as well. It was found that the fluid formed a vortex in each separation cell relative to the rotating reference frame. The magnitude of the tangential velocity and that of radial velocity significantly changed with the speed of rotation. The flow rate had insignificant impact on the tangential velocity and the radial velocity.

Theoretical and Experimental Investigation on Tip Forces and Temperature Distributions of the Brush Seal Coupled Aerodynamic Force

Based on a type of three-dimensional slice model of a brush seal combined with the commercial CFD software FLUENT, the study calculated the leakage flow of the brush seal. The aerodynamic forces applied on upstream and downstream bristles are analyzed and reduced to a smaller amount of point forces for analysis convenience. The frictional coefficient between the bristle material Haynes 25 and rotor material 1Cr14Mn14Ni are tested. Tip forces including normal reaction and frictional forces caused by aerodynamic forces are quantitatively investigated under conditions with and without frictions using the torque balance principle and nonlinear beam theory (by ANSYS simulations), respectively. Torques, frictional heats, and the temperature distributions of the rotor and bristle pack are studied further. Details and characteristics of the flow and temperature distributions inside the bristle pack are presented. In the experiments, besides traditional tests, such as leakage and torque tests, an infrared camera is employed to capture temperature distributions at the interface of the rotor, bristle pack and nearby zones under various pressure differentials and rotation speeds. The three-dimensional slice model is firstly verified by calculating the leakages, torques and temperature distributions of the brush seal and confirmed via experimentation. The influence of various frictional coefficients and pressure differentials on tip forces, torque and temperature distributions are also examined.

Estimation of bird fatalities at wind farms with complex topography and vegetation in Hokkaido, Japan

AbstractWorldwide expansion in wind‐energy generation has raised concerns about bird collisions—in particular, protected species. Bird collision studies are common in Europe and USA, but none had been done in Japan to date. We studied bird fatalities at 42 turbines (52.8 MW) in Tomamae, northern Hokkaido, Japan. For 17 months from July 2007 to November 2008, we performed 24 fatality surveys at an average 21‐day interval and ≤100 m from the wind turbines. We found 52 fatalities, including 4 white‐tailed eagles (Haliaeetus albicilla). Our estimate of the adjusted annual mortality at Tomamae, which used a modified equation to factor in the complex topography and dense vegetation spread generically over Japan, was 2.20 bird fatalities/MW/year and 0.36 raptor fatalities/MW/year. Bird utilization rates explained most of the variation in fatality rates among species and among locations. The highest fatality rates occurred at the turbines on a costal cliff where the rotor zones of wind turbines overlapped the frequent flight paths of large birds. The development of generalized models can be useful for predicting the impacts of other wind projects on birds, with the exceptions of high‐risk situations. However, more surveys of fatality rates and utilization rates are required at this and additional study sites, and over a longer period with shorter search intervals, to develop predictive models of bird collisions with general applicability. © 2013 The Wildlife Society.

Device for passive flow control around vertical axis marine turbine

The power supplied by a turbine with the rotor placed in a free stream flow may be increased by augmenting the velocity in the rotor area. The energy of the free flow is dispersed and it may be concentrated by placing a profiled structure around the bare turbine in order to concentrate more energy in the rotor zone. At the Aerodynamic and Wind Engineering Laboratory (LAIV) of the Technical University of Civil Engineering of Bucharest (UTCB) it was developed a concentrating housing to be used for hydro or aeolian horizontal axis wind turbines, in order to increase the available energy in the active section of turbine rotor. The shape of the concentrating housing results by superposing several aero/hydro dynamic effects, the most important being the one generated by the passive flow control devices that were included in the housing structure. Those concentrating housings may be also adapted for hydro or aeolian turbines with vertical axis. The present paper details the numerical research effectuated at the LAIV to determine the performances of a vertical axis marine turbine equipped with such a concentrating device, in order to increase the energy quantity extracted from the main flow. The turbine is a Darrieus type one with three vertical straight blades, symmetric with respect to the axis of rotation, generated using a NACA4518 airfoil. The global performances of the turbine equipped with the concentrating housing were compared to the same characteristics of the bare turbine. In order to validate the numerical approach used in this paper, test cases from the literature resulting from experimental and numerical simulations for similar situations, were used.

Epicardial Ablation of Rotors Suppresses Inducibility of Acetylcholine-Induced Atrial Fibrillation in Left Pulmonary Vein–Left Atrium Preparations in a Beagle Heart Failure Model

The purpose of this study was to provide direct evidences that rotor ablation suppresses atrial fibrillation (AF) inducibility. Micro-re-entrant wavefronts have been suggested to serve as sources of rapid activations during AF. Whether AF inducibility is suppressed by elimination of rotors remains unknown. We used optical mapping to study Langendorff-perfused left pulmonary vein (PV)-left atrium (LA) preparations from 13 dogs with pacing-induced heart failure. Atrial arrhythmias were induced by pacing and mapped during acetylcholine infusion (1 μmol/l). Rotors were identified from optical recordings. Epicardial ablation was performed targeting the rotor anchoring sites in preparations with sustained (>10 min) or incessant spontaneous AF. Non-rotor ablation was performed in 4 preparations. Repeated pacing was performed to test the AF inducibility after ablation. Sustained AF (n = 12) and incessant spontaneous AF (n = 1) were induced after acetylcholine infusion. Pulmonary vein focal discharge was found in 9 preparations (9.2 ± 4.2 beats/s), and rotor anchoring was found at the left superior PV-LA junction in 13 preparations (9.1 ± 4.6 beats/s) and at the ligament of Marshall-PV-LA junction in 1 preparation. Epicardial rotor ablation successfully inhibited the inducibility of sustained AF in 12 of 13 preparations (p < 0.01), including 4 with the maximal dominant frequency sites located on the PV-LA junctional rotor zones (direct elimination of mother rotors). The longest AF duration was shortened significantly by rotor ablation (Wilcoxon Z = 3.60, p = 0.002, n = 13), but not by non-rotor ablation (Wilcoxon Z = 1.00, p = 0.317, n = 4). Epicardial ablation of the rotor anchoring sites suppresses AF inducibility. The arrhythmogenicity at the maximal dominant frequency sites is directly/indirectly suppressed by the rotor ablation.

Response of raptors to a windfarm

Summary1. The global growth of wind energy has outpaced our assessment of possible impacts on wildlife. There is a pressing need for studies with pre‐ and post‐construction data to determine whether wind facilities will have detrimental effects on susceptible avian groups such as raptors.2. A pre‐ and post‐construction study was conducted to determine the impact of a windfarm on the abundance and behaviour of raptors in Wisconsin, USA. Variation in abundance and behaviour was examined both within and among years and relative to selected spatial, temporal and weather covariates. Raptor avoidance rates and indices of collision risk were calculated.3. Raptor abundance post‐construction was reduced by 47% compared to pre‐construction levels. Flight behaviour varied by species, but most individuals remained at a distance of at least 100 m from turbines and above the height of the rotor zone.4. Turkey vultures Cathartes aura and red‐tailed hawks Buteo jamaicensis displayed high‐risk flight behaviours more often than all other raptor species, but also showed signs of avoidance. Red‐tailed hawks were the only raptor species found dead beneath turbines during mortality searches. There were few observed mortalities and corrected mortality estimates were comparable to those from other windfarm studies.5. Synthesis and applications. The decline in raptor abundance post‐construction together with other lines of evidence suggests some displacement from the windfarm project area. While certain species may be at risk, flight behaviour data and mortality estimates indicate that the majority of raptors may not be directly affected by the presence of turbines. The avoidance rates recorded in this study should be used to improve collision risk models, and both current and future windfarms should investigate avoidance behaviour post‐construction.

Influence of Behavior on Bird Mortality in Wind Energy Developments

ABSTRACT As wind power generation is rapidly expanding worldwide, there is a need to understand whether and how preconstruction surveys can be used to predict impacts and to place turbines to minimize impacts to birds. Wind turbines in the 165‐km2 Altamont Pass Wind Resource Area (APWRA), California, USA, cause thousands of bird fatalities annually, including hundreds of raptors. To test whether avian fatality rates related to rates of utilization and specific behaviors within the APWRA, from March 1998 to April 2000 we performed 1,959 30‐minute behavior observation sessions (360° visual scans using binoculars) among 28 nonoverlapping plots varying from 23 ha to 165 ha in area and including 10–67 turbines per plot, totaling 1,165 turbines. Activity levels were highly seasonal and species specific. Only 1% of perch time was on towers of operating turbines, but 22% was on towers of turbines broken, missing, or not operating. Of those species that most often flew through the rotor zone, fatality rates were high for some (e.g., 0.357 deaths/megawatt of rated capacity [MW]/yr for red‐tailed hawk [Buteo jamaicensis] and 0.522 deaths/MW/yr for American kestrel [Falco sparverius]) and low for others (e.g., 0.060 deaths/MW/yr for common raven [Corvus corax] and 0.012 deaths/MW/yr for turkey vulture [Cathartes aura]), indicating specific behaviors or visual acuity differentiated these species by susceptibility to collision. Fatality rates did not correlate with utilization rates measured among wind turbine rows or plots for any species except burrowing owl (Athene cunicularia) and mallard (Anas platyrhynchos). However, mean monthly fatality rates of red‐tailed hawks increased with mean monthly utilization rates (r2 = 0.67) and especially with mean monthly flights through turbine rows (r2 = 0.92). Fatality rates increased linearly with rates of utilization (r2 = 0.99) and flights near rotor zones (r2 = 1.00) for large raptor species and with rates of perching (r2 = 0.13) and close flights (r2 = 0.77) for small non‐raptor species. Fatalities could be minimized or reduced by shutting down turbines during ≥1 season or in very strong winds or by leaving sufficiently large areas within a wind farm free of wind turbines to enable safer foraging and travel by birds.

Aerodynamic design by jointly applying S2 flow surface calculation and modern optimization methods on multistage axial turbine

A three-stage axial turbine was redesigned by jointly applying S2 flow surface direct problem calculation methods and multistage local optimization methods. A genetic algorithm and artificial neural network were jointly adopted during optimization. A three-dimensional viscosity Navier-Stokes equation solver was applied for flow computation. H-O-H-topology grid was adopted as computation grid, that is, an H-topology grid was adopted for inlet and outlet segment, whereas an O-topology grid was adopted for stator zone and rotor zone. Through the optimization design, the total efficiency increases 1.1%, thus indicating that the total performance is improved and the design objective is achieved.

Influence of Splitter Blades on the Flow Field of a Centrifugal Pump: Test-Analysis Comparison

This work aims at studying the influence of adding splitter blades on the performance of a hydraulic centrifugal pump. The studied machine is an ENSIVAL-MORET MP 250.200.400 pump (diameter=408 mm, 5 blades, specific speed=32), whose impeller is designed with and without splitter blades. Velocity and pressure fields are computed using unsteady Reynolds-averaged Navier-Stokes (URANS) approach at different flow rates. The sliding mesh method is used to model the rotor zone motion in order to simulate the impeller-volute casing interaction. The flow morphology analysis shows that, when adding splitter blades to the impeller, the impeller periphery velocities and pressures become more homogeneous. An evaluation of the static pressure values all around the impeller is performed and their integration leads to the radial thrust. Global and local experimental validations are carried out at the rotating speed of 900 rpm, for both the original and the splitter blade impellers. The head is evaluated at various flow rates: 50%, 80%, 100%, and 120%of the flow rate at the best efficiency point (BEP). The pressure fluctuations are measured at four locations at the BEP using dynamic pressure sensors. The experimental results match the numerical predictions, so that the effect of adding splitter blades on the pump is acknowledged. Adding splitters has a positive effect on the pressure fluctuations which decrease at the canal duct.