Rotor Casing Research Articles

New exact solution of Euler’s equations (rigid body dynamics) in the case of rotation over the fixed point

A new exact solution of Euler’s equations (rigid body dynamics) is presented here. All the components of angular velocity of rigid body for such a solution differ from both the cases of symmetric rigid rotor (which has two equal moments of inertia: Lagrange’s or Kovalevskaya’s case), and from the Euler’s case when all the applied torques are zero, or from other well-known particular cases. The key features are the next: the center of mass of rigid body is assumed to be located at meridional plane along the main principal axis of inertia of rigid body, besides, the principal moments of inertia are assumed to satisfy to a simple algebraic equality. Also, there is a restriction at choosing of initial conditions. Such a solution is also proved to satisfy to Euler–Poinsot equations, including invariants of motion and additional Euler’s invariant (square of the vector of angular momentum is a constant). So, such a solution is a generalization of Euler’s case.

Blade Tip Shape Optimization for Enhanced Turbine Aerothermal Performance

In high-speed, unshrouded turbines, tip leakage flows generate large aerodynamic losses and intense unsteady thermal loads over the rotor blade tip and casing. The stage-loading and rotational speeds are steadily increased to achieve higher turbine efficiency, and hence, the overtip leakage flow may exceed the transonic regime. However, conventional blade tip geometries are not designed to cope with supersonic tip flow velocities. A great potential lies in the modification and optimization of the blade tip shape as a means to control the tip leakage flow aerodynamics, limit the entropy production in the overtip gap, manage the heat-load distribution over the blade tip, and improve the turbine efficiency at high-stage loading coefficients. The present paper develops an optimization strategy to produce a set of blade tip profiles with enhanced aerothermal performance for a number of tip gap flow conditions. The tip clearance flow was numerically simulated through two-dimensional compressible Reynolds-averaged Navier–Stokes (RANS) calculations that reproduce an idealized overtip flow along streamlines. A multiobjective optimization tool, based on differential evolution combined with surrogate models (artificial neural networks), was used to obtain optimized 2D tip profiles with reduced aerodynamic losses and minimum heat transfer variations and mean levels over the blade tip and casing. Optimized tip shapes were obtained for relevant tip gap flow conditions in terms of blade thickness to tip gap height ratios (between 5 and 25) and blade pressure loads (from subsonic to supersonic tip leakage flow regimes), imposing fixed inlet conditions. We demonstrated that tip geometries that perform superior in subsonic conditions are not optimal for supersonic tip gap flows. Prime tip profiles exist, depending on the tip flow conditions. The numerical study yielded a deeper insight on the physics of tip leakage flows of unshrouded rotors with arbitrary tip shapes, providing the necessary knowledge to guide the design and optimization strategy of a full blade tip surface in a real 3D turbine environment.

A case of a human ventricular fibrillation rotor localized to ablation sites for scar-mediated monomorphic ventricular tachycardia

Ventricular tachycardia (VT) and ventricular fibrillation (VF) are the most common causes of sudden cardiac death. Currently, knowledge of the reentrant mechanism of monomorphic VT circuits in relation to complex scar anatomy allows for various mapping techniques including electroanatomic and entrainment mapping to accomplish catheter ablation of VT.1, 2 Clinically, it may be observed that ablation to eliminate recurrent macro-reentrant VT may also eliminate recurrent VF, as defined for instance by electrograms from implanted cardioverter-defibrillators (ICD).3, 4 However, whether this represents elimination of the VT trigger for VF, or directly of the substrate for VF, is unclear since the mechanism of VF in relation to scar is not known. Recent work targeting localized rotors in atrial fibrillation ablation has shown promise,5 but its implications for VF are unknown. We report here a case where VT termination and a VF rotor occurred at spatially coincidental sites in a patient with ischemic cardiomyopathy, suggesting that VF rotors may localize to the same anatomic substrate that promotes VT.

에너지보존과 토크평형을 이용한 제로터 유압 펌프/모터의 배제용적 해석 - 내·외부로터 회전 경우 -

It is difficult to analytically derive a volumetric displacement formula of gerotor hydraulic pump/motor because geometric shape of rotors is complicated. An analytical method about the volumetric displacement is proposed in this work, which is relatively easy and based upon two physical concepts. The first one is energy conservation between hydraulic energy of the pump/motor and mechanical input/output energy. The second concept is torque equilibrium with respect to inner and outer rotors. The formula about the volumetric displacement is derived for the common case of inner and outer rotors rotate with respect to fixed axes. The formula is verified by comparing another analytical displacement formula, and it is numerically verified by comparing numerical results, which is calculated for geometric specification of a motor. The numerical displacement is calculated through CAD software program and MATLAB program. The proposed analytical formula can be utilized in analysis and design of hydraulic gerotor motors.

Tip Leakage Flow and Heat Transfer on Turbine Blade Tip and Casing, Part 1: Effect of Tip Clearance Height and Rotation Speed

Steady simulations were performed to investigate tip leakage flow and heat transfer characteristics on the rotor blade tip and casing in a single-stage gas turbine engine. A typical high-pressure gas turbine stage was modeled with a pressure ratio of 3.2. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data under similar operating condition. The present numerical study focuses extensively on the effects of tip clearance heights and rotor rotational speeds on the blade tip and casing heat transfer characteristics. It was observed that the tip leakage flow structure is highly dependent on the height of the tip gap and the speed of the rotor. In all cases, the tip leakage flow was seen to separate and recirculate just around the corner of the pressure side of the blade tip. This region of re-circulating flow enlarges with increasing clearance heights. The separated leakage flow reattaches afterwards on the tip surface. Leakage flow reattachment was shown to enhance surface heat transfer at the tip. The interaction between tip leakage flow and secondary flows that is induced by the relative casing motion is found to significantly influence the blade tip and casing heat transfer distribution. A region of critical heat transfer exists on the casing near the blade tip leading edge and along the pressure-side edge for all the clearance heights that were investigated. At high rotation speed, the region of critical heat transfer tends to move towards the trailing edge due to the change in inflow angle.

Exploration of a new-type grooved casing treatment configuration for a high-speed small-size centrifugal compressor

The main design target for a casing treatment device is to increase the stall margin of a given compressor without sacrificing efficiency. In this article, numerical and experimental investigations about a new-type grooved casing treatment configuration are presented for a high-speed small-size centrifugal compressor. Different from traditional grooved casing treatments, in which the grooves are always placed over the rotor (for both axial and radial compressors), one or several circumferential casing grooves are placed along the shroud side of the diffuser passage in this configuration, to enhance the stall margin of the compressor. Computational fluid dynamics analysis is performed under stage environment in order to find the optimum location of the circumferential casing groove for the subsequent experiments in consideration of stall margin enhancement and peak efficiency gain, and the impact of groove number to the effect of this new-type grooved casing treatment configuration in enhancing the stall margin of the compressor stage is studied. It is found that stall margin gain due to the existence of circumferential casing grooves arises from the suction–reinjection effect of the low momentum fluid and its transportation along the circumferential and streamwise directions in the grooves and the grooves located at the middle and rear part of the diffuser casing wall have more pronounced effect in expanding the stall margin of the centrifugal compressor. In order to verify the effectiveness of this new-type grooved casing treatment configuration, the solid casing compressor and the compressors with circumferential casing grooves are tested in our test rig. The results indicate that this new-type grooved casing treatment configuration can obtain obvious improvement in the stall margin without sacrificing peak efficiency. Also, the numerical investigation is conducted for the entire compressor with circumferential casing grooves and the result is compared with the experimental data.

The Spiral Groove Bearing as a Mechanism for Enhancing the Secondary Flow in a Centrifugal Rotary Blood Pump

The rapid evolution of rotary blood pump (RBP) technology in the last few decades was shaped by devices with increased durability, frequently employing magnetic or hydrodynamic suspension techniques. However, the potential for low flow in small gaps between the rotor and pump casing is still a problem for hemocompatibility. In this study, a spiral groove hydrodynamic bearing (SGB) is applied with two distinct objectives: first, as a mechanism to enhance the washout in the secondary flow path of a centrifugal RBP, lowering the exposure to high shear stresses and avoiding thrombus formation; and second, as a way to allow smaller gaps without compromising the washout, enhancing the overall pump efficiency. Computational fluid dynamics was applied and verified via bench-top experiments. An optimization of selected geometric parameters (groove angle, width and depth) focusing on the washout in the gap rather than generating suspension force was conducted. An optimized SGB geometry reduced the residence time of the cells in the gap from 31 to 27 ms, an improvement of 14% compared with the baseline geometry of 200 μm without grooves. When optimizing for pump performance, a 15% smaller gap yielded a slightly better rate of fluid exchange compared with the baseline, followed by a 22% reduction in the volumetric loss from the primary pathway. Finally, an improved washout can be achieved in a pulsatile environment due to the SGB ability to pump inwardly, even in the absence of a pressure head.

Analysis of the Unsteady Overtip Casing Heat Transfer in a High Speed Turbine

In modern gas turbine engines, the rotor casing is vulnerable to thermal failures due to large unsteady heat fluxes. The rotor tip flow unsteadiness is induced by the periodic passage of the rotor blades, with an intensity dependent on the tip gap geometry. Hence, the understanding of the physics is of paramount importance to develop appropriate predictive tools and improve the cooling schemes. The present research aims at providing essential information on the flow conditions, which should serve to assess the relative impact of the overtip flow, tip gap magnitude, and work extraction processes on the casing thermal load. This paper presents simultaneous measurements of steady and unsteady heat transfer, pressure and rotor tip clearance in the casing of a transonic turbine stage. The research article was tested in a compression tube facility operating at engine representative conditions (vane Mach number 1.07, vane outlet Reynolds number 1.3 × 106, pressure ratio is 2.92, at 6790 rpm). The rotor blade geometry has a flat tip with a nominal tip clearance of about 0.4% of blade height. The heat transfer, pressure, and tip clearance data were obtained at three circumferential positions around the turbine casing. The heat flux was monitored using a single-layered thin film gauge able to resolve with high fidelity the wall temperature fluctuations. The heat flux sensor was mounted on a probe equipped with a heating device that allows varying the wall temperature. A series of experiments was performed at different heating rates to derive the local adiabatic wall temperature and the adiabatic convective heat transfer coefficient. A high bandwidth capacitive sensor provided the instantaneous value of the single blade tip clearance. A simple zero-dimensional model has been proved effective to predict the local flow temperature while the rotor spins up prior to the test, and estimate the overtip flow temperature during a test.

Fault Diagnosis of Motor Rotor Based on Fuzzy C-Means Clustering Analysis

For the fuzziness of the fault symptoms in motor rotor, this paper proposes a fault diagnostic method which based on the time-domain statistical features and the fuzzy c-means clustering analysis (FCM). This method is to extract the characteristic features of time-domain signal via time-domain statistics and to import the extracted characteristic vector to classifier. And then the fuzzy c-means realizes the classification by confirming the distance among samples, which is based on the degree of membership between the sample and the clustering center. The fault diagnostic cases of motor rotor show that the method which bases on the time-domain statistical features-FCM can detect the rotor fault effectively and distinguish the different types of fault correctly. Therefore, it can be used as an important means of rotor fault identification.

Effect of Aggressive Inlet Swirl on Heat Transfer and Aerodynamics in an Unshrouded Transonic HP Turbine

Swirling flows are now widely being used in modern gas turbine combustors to improve the combustion characteristics, flame stability, and reduce emissions. Residual swirl at the combustor exit will affect the performance of the downstream high-pressure (HP) turbine. In order to perform a detailed investigation of the effect of swirl on a full-scale HP turbine stage, a combustor swirl simulator has been designed and commissioned in the Oxford Turbine Research Facility (OTRF), previously located at QinetiQ, Farnborough UK, as the Turbine Test Facility (TTF). The swirl simulator is capable of generating engine-representative combustor exit swirl distributions at the turbine inlet, with yaw and pitch angles of up to ± 40 deg. The turbine test facility is an engine scale, short duration, rotating transonic turbine facility, which simulates the engine representative M, Re, Tu, nondimensional speed, and gas-to-wall temperature ratio at the turbine inlet. The test turbine is a highly loaded unshrouded design (the MT1 turbine). This paper presents time-averaged experimental heat transfer measurements performed on the rotor casing surface, and on the rotor blade surface at 10%, 50%, and 90% span. Time-averaged rotor casing static pressure measurements are also presented. Experimental measurements with and without inlet swirl are compared. The measurements are discussed with the aid of three-dimensional steady and unsteady CFD simulations of the turbine stage. Numerical simulations were conducted using the Rolls-Royce in-house code HYDRA, with and without inlet swirl.

Reduction of Tip Clearance Losses in an Unshrouded Turbine by Rotor Casing Contouring

Tip leakage flow is responsible for a number of aerodynamic losses in turbines, and the mixing of tip leakage flow with the passage secondaryflowcauses significant losses. This paperpresents a numerical investigation of the effect of three types of casing contouring: 1) step, 2) trench, and 3) arc casings on aerodynamic performance of anunshrouded turbine rotor at design and off-design incidences, in an attempt to seek an optimal casing contour with the objective both of avoiding direct tip leakage in the tip clearance, and of efficiently using the interaction between the tip leakage vortex and passage vortex inside rotor passage, and then to reduce the total losses in turbines. The results show that the reduction in tip leakage losses obtained by the optimized casing contour significantly overrides the losses caused by the step in theflowpath. Introduction of casing step thickens the inlet boundary layer, which increases the strength of the tip passage vortex and hence suppresses the evolution of the tip leakage vortex. Step and trench casings provide the largest efficiency increase when the inlet flow direction is normal to the casing step while arc casing achieves the best performance improvement at the design incidence.

Reduction of Tip Clearance Losses in an Unshrouded Turbine by Rotor Casing Contouring

Reduction of Tip Clearance Losses in an Unshrouded Turbine by Rotor Casing Contouring

A computational investigation of the transient response of an unbalanced rigid rotor flexibly supported and damped by short magnetorheological squeeze film dampers

Due to manufacturing and assembly inaccuracies, real rotors are always slightly imbalanced. This produces their lateral vibration and forces that are transmitted through the bearings to the stationary parts. The oscillation of the system can be reduced if damping devices are added to the constraint elements. To achieve the optimum performance of the rotor in a wide range of angular velocities and when passing through the critical speeds their damping effect must be controllable. For this purpose, the application of semiactive magnetorheological (MR) dampers has been analysed. The investigated problem focuses on studying the influence of their damping effect and of its control on the amplitude of the rotor vibration, on the magnitude of the force transmitted to the rotor casing, and on the amount of dissipative power generated in the MR films. The developed mathematical model assumes cavitation in the lubricating layer, and the MR liquid is modelled as a Bingham material. The derivation of the equation governing the pressure distribution in the oil film is completed by a new methodology making it possible to determine the yielding shear stress needed for its solution. The equations of motion of the rotor are nonlinear due to the damping forces and to solve them a Runge–Kutta integration method was applied. Computer simulations show that a suitably proposed current–rotor angular speed relationship enables one to fully eliminate the resonance peaks and to achieve the optimum compromise between the attenuation of the rotor lateral vibration, the magnitude of the forces transmitted to the rotor casing and the amount of energy dissipated in the lubricating layers.

Design optimization and fabrication of a hybrid composite flywheel rotor

This paper discusses three different rim design cases of a hybrid composite flywheel rotor using strength ratio optimization. The rotor is composed of four hybrid composite rims. These rims are made from carbon–glass/epoxy with varying volume fractions of hoop wound reinforcements. Optimization is performed to reduce the maximum strength ratio during two rotor states: stationary and the maximum allowable rotational speed. The input specifications for optimization are: maximum useable energy (35kWh), rotational speed (15,000rpm), height, and inner radius. In the first case, the rims are wound simultaneously by continuous winding. However, in the second case, the rims are wound separately, and interferences are incorporated for their assembly by press fit. In the third case, a hybrid version of the first two cases is used, whereby two pairs of rims are wound at the same time, and in a secondary operation, the first pair is press fitted to the second pair. Each case has different fabrication costs and different strength ratios. The third case rotor has been successfully manufactured by filament winding with in situ curing, followed by press fit assembly of machined rims.

Technological and economical analysis of salient pole and permanent magnet synchronous machines designed for wind turbines

Chinese export restrictions already reduced the planning reliability for investments in permanent magnet wind turbines. Today the production of permanent magnets consumes the largest proportion of rare earth elements, with 40% of the rare earth-based magnets used for generators and other electrical machines. The cost and availability of NdFeB magnets will likely determine the production rate of permanent magnet generators. The high volatility of rare earth metals makes it very difficult to quote a price. Prices may also vary from supplier to supplier to an extent of up to 50% for the same size, shape and quantity with a minor difference in quality.The paper presents the analysis and the comparison of salient pole with field winding and of peripheral winding synchronous electrical machines, presenting important advantages. A neodymium alloy magnet rotor structure has been considered and compared to the salient rotor case. The Salient Pole Synchronous Machine and the Permanent Magnet Synchronous Machine were designed so that the plate values remain constant. The Eddy current effect on the windings is taken into account during the design, and the efficiency, output power and the air-gap flux density obtained after the simulation were compared. The analysis results clearly indicate that Salient Pole Synchronous Machine designs would be attractive to wind power companies. Furthermore, the importance of the design of electrical machines and the determination of criteria are emphasized. This paper will be a helpful resource in terms of examination and comparison of the basic structure and magnetic features of the Salient Pole Synchronous Machine and Permanent Magnet Synchronous Machine. Furthermore, an economic analysis of the designed machines was conducted.

Processing of Advanced Cast Alloys for A-USC Steam Turbine Applications

The high-temperature components within conventional supercritical coal-fired power plants are manufactured from ferritic/martensitic steels. To reduce greenhouse-gas emissions, the efficiency of pulverized coal steam power plants must be increased to as high a temperature and pressure as feasible. The proposed steam temperature in the DOE/NETL Advanced Ultra Supercritical power plant is high enough (760°C) that ferritic/martensitic steels will not work for the majority of high-temperature components in the turbine or for pipes and tubes in the boiler due to temperature limitations of this class of materials. Thus, Ni-based superalloys are being considered for many of these components. Off-the-shelf forged nickel alloys have shown good promise at these temperatures, but further improvements can be made through experimentation within the nominal chemistry range as well as through thermomechanical processing and subsequent heat treatment. However, cast nickel-based superalloys, which possess high strength, creep resistance, and weldability, are typically not available, particularly those with good ductility and toughness that are weldable in thick sections. To address those issues related to thick casting for turbine casings, for example, cast analogs of selected wrought nickel-based superalloys such as alloy 263, Haynes 282, and Nimonic 105 have been produced. Alloy design criteria, melt processing experiences, and heat treatment are discussed with respect to the as-processed and heat-treated microstructures and selected mechanical properties. The discussion concludes with the prospects for full-scale development of a thick section casting for a steam turbine valve chest or rotor casing.

Effect of turbine inlet temperature on rotor blade tip leakage flow and heat transfer

PurposeOne of the most critical gas turbine engine components, the rotor blade tip and casing, is exposed to high thermal load. It becomes a significant design challenge to protect the turbine materials from this severe situation. The purpose of this paper is to study numerically the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer.Design/methodology/approachIn this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (LTIT: 444 K) and high (HTIT: 800 K) turbine inlet temperature, as well as non‐uniform inlet temperature have been considered.FindingsThe results showed the higher turbine inlet temperature yields the higher velocity and temperature variations in the leakage flow aerodynamics and heat transfer. For a given turbine geometry and on‐design operating conditions, the turbine power output can be increased by 1.33 times, when the turbine inlet temperature increases 1.80 times. Whereas the averaged heat fluxes on the casing and the blade tip become 2.71 and 2.82 times larger, respectively. Therefore, about 2.8 times larger cooling capacity is required to keep the same turbine material temperature. Furthermore, the maximum heat flux on the blade tip of high turbine inlet temperature case reaches up to 3.348 times larger than that of LTIT case. The effect of the interaction of stator and rotor on heat transfer features is also explored using unsteady simulations. The non‐uniform turbine inlet temperature enhances the heat flux fluctuation on the blade tip and casing.Originality/valueThe increase of turbine inlet temperature is usually proposed to achieve the higher turbine efficiency and the higher turbine power output. However, it has not been reported how much the heat transfer into the blade tip and casing increases with the increased turbine inlet temperature. This paper investigates the heat transfer distributions on the rotor blade tip and casing, associated with the tip leakage flow under high and low turbine inlet temperatures, as well as non‐uniform temperature distribution.

Mesh Deformation Method for Rotor Flows

Helicopter blades experience large in-flight deformations that affect the aerodynamics of the rotor. Consequently, computational fluid dynamics (CFD) methods applied to helicopter flows must have appropriate algorithms to account for the blade deformation without deterioration in the CFD mesh quality. In this work, a hybrid mesh deformation method, suitable for use with helicopter blades, is proposed. The method begins by accounting for the blade deformation using a modal structural model. The interpolation between the finite element and CFD meshes for the blade surface is based on the constant-volume tetrahedron method and is combined with transfinite interpolation as well as the spring analogy method. The final algorithm is efficient and resulted in deformed meshes with good qualities. A range of rotor cases were considered, and the changes in volume of the CFD cells were less than 30% of their original values. The cell skewness was also kept at acceptable levels. The mesh deformation method was coupled with the helicopter multiblock CFD solver, and computations were undertaken for rigid and deformed blades. It was found that the structural deformation affected the blade loads even for hovering rotor cases, although it had a more pronounced effect in forward flight. The mesh method was efficient and accounted for less than 1% of the total central processing unit time.

Investigation of Vibration Mitigation of Flexibly Support Rigid Rotors Equipped with Controlled Elements

Abstract The subject of investigations presented in this article is achieving the optimum attenuation of lateral vibration of rotors by means of two design variants of constraint elements: semiactive magnetorheological squeeze film dampers and actively controlled hydrodynamic bearings. The damping effect of magnetorheological dampers is controlled by the change of magnetic flux generated in electric coils and of the hydrodynamic bearings by the change of magnitude of the proportional gain of a feedback controller exciting movement of the bearing housings. In the developed mathematical models the rotor is considered as absolutely rigid and the controllable constraint elements are represented by force couplings. The rotor turns at constant angular speed, is loaded by its weight and in addition it is excited by a centrifugal force caused by the disc unbalance. In both design cases its lateral vibration is governed by a nonlinear equation of motion. The pressure distribution in the lubricating film in the magnetorheological squeeze film damper is described by a Reynolds equation modified for Bingham fluid whose yield shear stress depends on magnetic induction. The hydraulic forces acting in the hydrodynamic bearings are determined for the case of π-film cavitation and position of the bearing housings is adjusted by actuators activated by a proportional feedback controller. The aim of the analysis is to deal with approaches leading to minimizing amplitude of the rotor steady state vibration and magnitude of the force transmitted into the rotor casing and to compare efficiency of both design variants. The performed computer simulations show that the arrangement with the magnetorheological squeeze film damper gives better results in reducing magnitude of the transmitted force than those when the rotor is supported by hydrodynamic bearings with actively controlled position of the bearing housings.

C111 非偏心回転式エンジン「イシノ・エンジン」の開発(2種類の特殊曲面ローターを用いた機関構成と体積変化過程)(OS-5: これからの燃焼研究(1))

A novel rotational internal combustion engine is invented and investigated. No eccentric rotational component is used in this engine, resulting in vibration-free operation. The engine consists of rotor casing and two types of rotor; cycloid rotor and trochoid rotor. The shape of the cycloid rotor is characterized by epicycloid surface, and the trochoid rotor also superior-epitrochoid surface. In this paper, first, the typical configuration is shown, next, two procedure for designing the rotors are described in detail. Furthermore the design drawing of the prototype engine is given and its cyclic behaivior, the time variations of the chamber volume and the estimated pressure are indicated. The result of detail investigation for geometry of the engine configuration shows that the most appropriate combination of numbers of cycloid tooth and trochoid cavity is Nc:Nt=2:3 for engine compactness and compression ratio.