Rotor Flow Field Research Articles

Experimental Study of Flow Field of Large Air-Cooled Turbine Generator for Multi-Ventilation Ducts of Stator

To study rotational air flow field of rotor and complicated flow distinction owing to multi-ventilation ducts of stator in a large air-cooled turbine generator, considering axial symmetry of air supply, an experiment setup of ventilation system of semi-machine configuration was built in this paper. At condition of rotating, ventilation is measured by hot-wire anemometer. Firstly, ventilation in 16 different semi-circle radius is got. Measurement shows that ventilation in different radius varies much. Then ventilation of outlet of stator ducts is measured. The result shows that ventilation which is affected by flow back and jet less is higher. The conclusion will provide theoretical references for ventilation cooling of rotor ducts in large air-cooled turbine generators.

A New Coupled Free Wake-CFD Method for Calculation of Helicopter Rotor Flow-Field in Hover

This paper concerns a new coupled free wake-CFD method for proper calculation of aerodynamic loads on a two bladed helicopter rotor in hovering flight. Loading is computed by solving the three dimensional Euler equations in a rotating coordinate system. However, since direct simulation of the tip vortices and wake requires a very fine grid, the rotor’s wake effects are modeled by a free wake approach and included into the CFD calculation by a transpiration boundary condition at the rotor surface. An influence coefficient solution method is used to find the rotor’s wake shape, being steady in a rotating frame. Euler equations are also considered in the form of absolute flow variables and solved by a multi grid Jameson’s finite-volume method. The accuracy of the proposed method is illustrated by comparing numerical results to the available experimental results for the pressure distribution on a blade of a model helicopter rotor at different tip Mach numbers.

Predicting Double-Blade Vertical Axis Wind Turbine Performance by a Quadruple-Multiple Streamtube Model

Abstract Double-blade vertical axis wind turbines (DB-VAWTs) can improve the self-starting performance of lift-driven VAWTs. We here propose the quadruple-multiple streamtube model (QMS), based on the blade element momentum (BEM) theory, for simulating DB-VAWT performance. Model validity is investigated by comparison to computational fluid dynamics (CFD) prediction for two kinds of two-dimensional DB-VAWT rotors for two rotor scales with three inner-outer radius ratios: 0.25, 0.5, and 0.75. The BEM-QMS model does not consider the effects of an inner rotor on the flow speed in the upwind half of the rotor, so we introduce a correction factor for this flow speed. The maximum power coefficient predicted by the modified BEM-QMS model for a DB-VAWT is thus closer to the CFD prediction. Keywords : Wind turbine, Double-blade rotor, VAWT, BEM, CFD, QMS. 1. Introduction Vertical axis wind turbines (VAWTs) offer lower costs due to the simplified mechanics, because the wind direction is unimportant to performance. However, small-scale lift-driven VAWTs typically have poor self-starting performance [1]. Therefore, a variety of steps have been tried to improve self-starting performance: increasing blade chord length, adding more blades, using drag-driven wind turbines as a starter, and designing blade airfoils for high aerodynamic performance (for example, [2]). Double-blade vertical axis wind turbines (DB-VAWTs), such as the one shown in Fig. 1 (a), are an example for improving self-starting performance. DB-VAWTs can produce larger starting torque than conventional single-rotor VAWTs with the same blade chord length. Figure 1(b) shows a new type of VAWT with multiple looped blades forming a double-blade rotor structure, as in a DB-VAWT. This VAWT was named the butterfly wind turbine (BWT) [3] because as it rotates around the vertical axis it has the shape of a butterfly. The BWT may offer reduced costs, good self-starting performance, high energy efficiency, and good vibration handling because of the direct installation of the armless looped blades on the central axis. Although propeller-type horizontal axis wind turbines (HAWTs) are the primary turbines for large-scale wind power generation, large-scale VAWTs have been recently proposed and developed for offshore wind power because of their low operational and maintenance costs [4]–[10]. A large-scale VAWT requires struts or arms that connect the blades and central rotating axis, and the cross-section of the struts should also be airfoils to reduce drag. These airfoil struts produce lift force if they incline against the horizontal plane, and so the structure can be regarded as a partial double-blade rotor. Since the flow field of a double-blade rotor is very complex, it is difficult to predict performance by using conventional blade

Coupled wind-wave time domain analysis of floating offshore wind turbine based on Computational Fluid Dynamics method

As offshore wind farms are extending into the deep sea around the world, the coupled aerodynamic and hydrodynamic time domain analysis of floating offshore wind turbine is of both profound academic interests and important practical interests. In this work, one typical tension leg platform of 5 MW wind turbine system has been chosen to the objective. The aerodynamic loads of the NREL 5 MW offshore wind turbine have been simulated based on Navier-Stokes equations and renormalization group (RNG) k-ε turbulence mode, which is suitable for the analysis of rotational flow field near wind turbine blades. The hydrodynamic loads of the floating wind turbine platform have been simulated by viscous numerical flume based on volume-of-fluid method. The dynamic responses of the floating wind turbine system could be obtained by solving the dynamic equations of the floating system under typical coupled wind-wave sea cases, and the motion of the floating platform under different time steps would be simulated by advanced sliding mesh technique. As a result, the fluid-structure interactions between the floating wind turbine structure and the coupled wind-wave flow field have been successfully simulated. Furthermore, the availability of the coupled numerical method has been verified by comparing the numerical results with corresponding scale model test data.

The Effects of Unsteadiness and Compressibility on the Interaction Between Hub Leakage and Mainstream Flows in High-Pressure Turbines

This paper investigates the effects of compressibility and unsteadiness due to the relative blade row motion and their importance in the interaction between hub leakage (purge) and mainstream flows. First, the challenges associated with the blade redesign for low-speed testing are described. The effects of Mach number are then addressed by analyzing the experiments in the low-speed linear cascade equipped with the secondary airflow system and computations performed on the low- and high-speed blade profiles. These results indicate that the compressibility does not significantly affect the interaction between the leakage and mainstream flows despite a number of compromises made during the design of the low-speed blade. This was due to the fact that the leakage–mainstream interaction takes place upstream of the blade throat where the local Mach numbers are still relatively low. The analysis is then extended to the equivalent full-stage unsteady computations. The periodic unsteadiness resulting from the relative motion of the upstream vanes appreciably affected the way in which the leakage flow is injected and the rotor flow field in general. However, the time-average flow field was still found to be dominated by the rotor blade's potential field. For the present test arrangement, the unsteady effects were not very detrimental and caused less than a 10% increase in the losses due to the leakage injection relative to the steady calculations.

Evaluation of Nano-Scale Rotors and Motors at Static Condition

The static performance of nano-scale rotor and the mechanical efficiency of micro rotors are important factors to evaluate rotary-wing NAVs. In this paper, two pairs of nano-scale rotors, which were formed with the same airfoil section for each pair, were compared to find the influence of chord distribution and twist distribution to rotor performance. A test bench was designed with highly sensitive mechanism systems in order to be able to measure the thrust and torque of nano-rotors accurately. The static performance of nano-scale rotors was evaluated experimentally with the test bench at ultra-low Re. And computations based on 3D unsteady incompressible Navier-Stokes solver with artificial compressibility were carried out as well to obtain the detailed flow field of nano rotor. It was found that the rotor figure of merit degraded a lot with size reduction. And the rotor solidity determined by chord distribution has a positive effect on the rotor thrust coefficient while pitch angle distribution influences the power coefficient. Flow field analysis indicated that the state of leading edge vortex might be the inherent reason of the difference of performance between rotors. The mechanical efficiency of several small motors were also compared which showed that the performance of small rotors decline with the reduction of size.

Experimental analysis of a Ranque–Hilsch vortex tube for optimizing nozzle numbers and diameter

A brass vortex tube with changeable parts is used to obtain the optimum nozzle intake numbers and diameter. The effects of inlet pressure and CF (cold fraction) are also investigated. Results illustrate that increasing the number of nozzles causes a temperature drop and the optimum nozzle diameter corresponds to quarter of vortex tube diameter. The distance between cold end orifice and nozzle intakes is investigated in this work and it is found that for a better performance, this distance should be decreased. A series of experiments conducted to investigate the CF effect on VT performance and an optimum amount for this parameter is found. A two-dimensional computational fluid dynamics simulation of a VT has been carried out as well. CFD code is applied to investigate the role of nozzle diameter on the temperature separation. The highly rotating flow field structure and its characteristic are simulated and analyzed with respect to various operating inlet pressure ranges and different CFs. Finally, some results of the CFD models are validated by the available experimental data, showing reasonable agreement for future development.

Tip Flow Unsteadiness and Blade Row Interactions for a Low-Speed Compressor Rotor

A numerical investigation has been conducted to determine the effects of self-excited tip-leakage flow unsteadiness, upstream stator wakes, and downstream blade row interactions on the performance prediction of a low-speed research compressor rotor. Calculations included a single blade row rotor configuration as well as two multiblade row configurations: one in which the rotor was modeled with an upstream stator and a second in which the rotor was modeled with a downstream stator. Steady-state and time accurate calculations were performed using a Reynolds averaged Navier–Stokes solver, and the results were compared with detailed experimental data at operating conditions corresponding to the compressor design point, near stall, and a midpoint between the two. Differences in the performance predictions between the three configurations were then used to determine the effect of the upstream stator wakes and the downstream blade row interactions. Results obtained show that for this compressor with rather large tip clearance time accurate calculations are a vast improvement over steady-state calculations, but the upstream stator wakes and the downstream blade row interactions have only a small effect on the numerical solution. In this paper, changes in the rotor flowfield due to the upstream and downstream stators are investigated and discussed to explain the limited impact of the stator wakes and downstream blade row interactions on this tip dominated flow. In addition, the unsteady nature of the rotor tip vortex at near stall conditions is discussed to explain the improvement of time accurate analysis over steady-state computations.

Experimental analysis of flow structure in contra-rotating axial flow pump designed with different rotational speed concept

As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head — flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carried out to understand the complicated internal flow structures in the rotors.

Assessment of various rotor tip geometries on a single stage gas turbine performance

Tip leakage loss introduces major part of losses of the rotor in axial gas turbines. Therefore, the rotor blade tip has a considerable effect on rotor efficiency. To understand the flow physics of the rotor tip leakage, we solve the flow field for different tip platforms (passive flow control) and by considering coolant tip injection (active flow control). Various blade tip configurations such as squealers and extensions on both pressure and suction sides, partial PS-squealer and flat tip with various tip clearances are generated. The computational domains are generated using unstructured prism layers for boundary layer resolution and unstructured, tetrahedral mesh for main flow. By using a finite volume CFD solver capable of solving RANS equations in an unstructured domain, the transonic compressible flow in the domain is solved. To capture the turbulent field in blade tip, shear stress transport (SST) k-ω model is employed. By using mixing plane approach, it is possible to couple outlet boundary of stator and inlet boundary of rotor and investigate the stator-rotor interaction in the rotor flow field and its consequence tip leakage flow. To investigate the combined effects of active and passive flow control measures in blade tip region, we simulate baseline geometry with and without tip coolant to show the effects of geometrical features of the rotor tip as well as the effect of tip coolant mass flow rate. Taking into account various rotor tip configurations and their tip leakage losses, it is possible to propose an optimum configuration.

A new representation of rotational flow fields satisfying Euler's equation of an ideal compressible fluid

A new representation of the solution to Euler's equation of motion is presented by using a system of expressions for compressible rotational flows of an ideal fluid. This is regarded as a generalization of Bernoulli's theorem to compressible rotational flows. The present expressions are derived from the variational principle. The action functional for the principle consists of the main terms of the total kinetic, potential and internal energies, together with three additional terms yielding the equations of continuity, entropy and a third term that provides the rotational component of velocity field. The last term has the form of scalar product satisfying gauge symmetry with respect to both translation and rotation. This is a generalization of the Clebsch transformation from a physical point of view. It is verified that the system of new expressions, in fact, satisfies Euler's equation of motion.

Micro-manipulation using rotational fluid flows induced by remote magnetic micro-manipulators

We present a non-contact manipulation method for micron scale objects using locally induced rotational fluid flows created by groups of untethered magnetic micro-manipulators. The magnetic micro-manipulators are rotated in a viscous fluid by an externally generated magnetic field to create rotational flows, which act to move micro-objects in the flow region. One single spherical micro-manipulator is used to manipulate one object at a time, while an array of micro-manipulators spin in synchrony on a surface patterned with magnetic micro-docks to create reconfigurable fluidic channels for simultaneous transportation of multiple objects. The induced rotational flow field and the resulting hydrodynamic forces on the micro-objects are studied using both finite element solutions and analytical models from previous studies. These results are compared with experiment to determine manipulation characteristics for the complex flows. Due to its untethered and non-contact operation, this micro-manipulation method could be used to quickly move fragile or non-fragile micro-objects in inaccessible or enclosed spaces such as in lab-on-a-chip devices.

Numerical Simulation of Rotor Flowfields Based on Several Spatial Discretization Schemes

Numerical Simulation of Rotor Flowfields Based on Several Spatial Discretization Schemes

Angular Velocity Formula for Turbulent Vortex Chamber Flows

Vortex separators are increasingly utilized to remove suspended solids from stormwater runoff. Understanding flow pat- terns in a confined vortex chamber is crucial when investigating the mechanisms of liquid-solid separation. The angular velocity of fluid motion around the vertical axis is a dominant parameter for determining fluid flow patterns and particle trajectories in a rotational flow field. In this paper, an angular velocity formula, based on the angular-impulse momentum principle coupled with the Rankine vortex model, is derived under steady flow conditions. Comparison of predicted results using this formula to experimental data from a previous study indicates a general agreement. The derived formula can be used to estimate the angular velocity of the rotational flow field in vortex separators with tangential inlet and without internal components. DOI: 10.1061/(ASCE)HY.1943-7900.0000547. © 2012 American Society of Civil Engineers. CE Database subject headings: Velocity; Vortices; Hydrodynamics; Shear stress; Stormwater management; Runoff. Author keywords: Angular velocity; Vortex chamber flow; Rotational flow; Hydrodynamic separator; Angular momentum; Average shear stress; Torque.

Numerical Simulation of Rotor Flow Field Based on Overset Grids and Several Spatial and Temporal Discretization Schemes

A numerical method based on solutions of Euler/Navier-Stokes (N-S) equations is developed for calculating the flow field over a rotor in hover. Jameson central scheme, van Leer flux-vector splitting scheme, advection upwind splitting method (AUSM) scheme, upwind AUSM/van Leer scheme, AUSM+ scheme and AUSMDV scheme are implemented for spatial discretization, and van Albada limiter is also applied. For temporal discretization, both explicit Runge-Kutta method and implicit lower-upper symmetric Gauss-Seidel (LU-SGS) method are attempted. Simultaneously, overset grid technique is adopted. In detail, hole-map method is utilized to identify intergrid boundary points (IGBPs). Furthermore, aimed at identification issue of donor elements, inverse-map method is implemented. Eventually, blade surface pressure distributions derived from numerical simulation are validated compared with experimental data, showing that all the schemes mentioned above have the capability to predict the rotor flow field accurately. At the same time, vorticity contours are illustrated for analysis, and other characteristics are also analyzed.

Investigation of the stall delay of a 5kW horizontal axis wind turbine using numerical method

In this paper, a three-dimensional (3D) computational fluid dynamics (CFD) model is constructed to test a 5kW horizontal axis wind turbine HAWT that was designed using BEM method. It is found that the power coefficient of 0.38 determined by the 3D CFD model is higher than 0.34 obtained by the BEM method. The difference should be due to the stall delay in the rotation flow field of the wind turbine model, which was confirmed by the simulation results that the flow remain attached to the blade surface when wind velocity has reached 20m/s. The behaviours of the flow separation were also investigated under different wind speed in order to improve the performance design of the wind turbine blade.

Transient Schemes for Capturing Interfaces of Free-Surface Flows

This article presents a new methodology for the development of Transient Interpolation for Capturing of Surfaces schemes suitable for the simulation of free-surface flows, which is given the acronym TICS. The newly developed approach is based on a switching strategy that combines a bounded high-order transient scheme with a bounded compressive transient scheme. Bounded high-order and compressive transient schemes are constructed by discretizing the transient term in the volume-of-fluid (r) equation over a temporal control-volume in a way similar to the discretization of the convection term over a spatial control-volume, allowing advances in building convective schemes to be exploited in the development of bounded high-order and compressive transient schemes. Following that approach, a bounded version of the second-order upwind Euler scheme is constructed (B-SOUE). The B-SOUE is used to develop a family of temporal compressive schemes that is denoted by the B-CEm family, where “m” refers to the slope of the scheme on a temporal normalized variable diagram. The TICS methodology is then applied to the B-SOUE scheme and the B-CEm family of schemes to create a new family of transient interface-capturing schemes that is designated by TICSm. The virtues of the TICSm family, in producing a steep interface for the volume-of-fluid (r) field that defines the volume fraction occupied by the different fluids in a computational domain, are demonstrated through results generated using two schemes of the family (TICS1.75 and TICS2.5). The accuracy of the new transient TICS schemes is compared to the first-order Euler scheme, the Crank-Nicolson scheme, and the B-SOUE scheme by solving four pure advection test problems (advection of hollow shapes in an oblique flow field and advection of a solid body in a rotational flow field) and one flow problem (the break of a dam) using both the SMART and the STACS convective schemes. Results, displayed in the form of interface contours, demonstrate that predictions obtained with TICS1.75 and TICS2.5 are far more accurate and less diffusive, preserving interface sharpness and boundedness at all Courant number values considered.

Investigation of unsteady flow in axial turbine stage

The never ending process to increase the efficiency of turbine stages introduced an idea to create an axial turbine stage test rig as part of closed loop transonic wind tunnel at Vyzkumny a zkusebni letecky ustav (VZLU). Studying of unsteady flow field behaviours in turbine stages is nowadays essential in the development process. Therefore, the test rig was designed with focusing on possibility of detailed studying of unsteady flow fields in turbine stages. New methodologies and new instrumentations were developed at VZLU and successfully integrated to gain valuable information from experiments with turbine stages. Two different turbine stages were tested during the facility introduction process. The measurement of these two models demonstrated how flexible the test rig is. One of them was an enlarged model of small gas turbine stage. The other was scaled-down model of stage of intermediate-pressure steam turbine. The external characteristics of both models were acquired during experiments as well as the detailed unsteady flow field measurement. Turbine stages were tested in various regimes in order to check the capabilities of the facility, methodology and instrumentation together. The paper presents results of unsteady flow field investigation in the enlarged turbine stage with unshrouded rotor. The interaction of structures developed in a stator with the rotor flow field is depicted and the influence of turbine load on evolution of secondary flows in rotor is analysed.

J144 管状火炎を用いた家庭用コージェネレーションシステム向け補助熱源器の開発(一般講演(4))

The purpose of this study is to develop the compact auxiliary heater using tubular flame for home CHP (combined heat and power). The tubular flame is formed in a rotating flow field by injecting the air-fuel mixture tangentially into the cylindrical chamber. Combustion gas of the tubular flame has a high heat transfer coefficient due to the swirl flow. The coiled tube and the inserted tube installed at the center of the coiled tube are used as a heat exchanger. Combustion gas flows through the gap between in coiled tube and inserted tube. The thermal efficiency is 87% based on LHV. In this study, the heat transfer characteristics of the coiled tube is reported.

数字全息粒子图像测速技术应用于旋转流场测量的研究

数字全息粒子图像测速技术应用于旋转流场测量的研究