Rotor Interface Research Articles

Dynamic modelling and stability analysis of aero-engine rotor system considering aerodynamics

Bolting joint is widely used in aero-engine, but the existing analysis theory of bolting joint interface strength connection completely ignores the aerodynamic load borne by blade and support disks. Therefore, in view of the aero-engine rotor system, we establish a bolt-flange connection blade-disk-drum joint model. Based on the l-stubs strength theory, considering three failure modes of bolt-flange interface stiffness, we study the connection strength of the disk-drum structure under aerodynamic force and bolt preload, and analyse the steady-state response of the rotor system under different connection states. The results show that the aerodynamic load will produce three kinds of yield phenomena on the rotor interface, and reduce the critical speed of the rotor system. Due to the stiffness loss of the connection interface, the critical speed of the rotor decreases and a subcritical resonance phenomenon occurs after the second critical speed. At the same time, the increase of interface contact damping results in the failure of vibration energy transfer between disk and drum, which makes the drum more susceptible to external excitation. By balancing bolt preload and interface friction coefficient, the influence of aerodynamic load on interface contact characteristics can be reduced, and the working efficiency of rotor system can be improved.

Improvement of energy conversion efficiency in traveling wave rotary ultrasonic motor by increasing friction coefficient

This article introduces a method of enhancing the energy conversion efficiency of a traveling wave rotary ultrasonic motor with a flexible rotor by increasing the friction coefficient at the stator–rotor interface. The increased friction coefficient leads to improvements in energy conversion efficiency by increasing the output power and reducing friction loss power. Experimental verification showed that the friction coefficient in the interface increased from 0.21 to 0.32, the maximum energy conversion efficiency increased from 36.8% to 46.3%, and the interface friction loss was reduced.

A Comparison of Static and Rotordynamic Characteristics for Three Types of Impeller Front Seals in a Liquid Oxygen Turbopump

Abstract Annular seals are widely used to minimize the leakage, and improve efficiency and rotordynamic stability in turbomachinery. In a liquid oxygen turbopump, the operating conditions of annular seals are harsher with the high-pressure cryogenic propellant. Researches show that the primary leakage of a liquid oxygen turbopump is from the front and rear shoulder seals of the impeller. Moreover, the impeller shoulder seal sustains the largest pressure drop and highest swirl velocity in machine. Therefore, the shoulder seal plays an important role in rotor stability and successful full load operation of the turbopump, due to the significant seal fluid response forces. Previous literature shows that the hole-pattern seal has excellent performance in rotordynamic characteristics, and its leakage rate shows a very weak sensitive to the rotating speed. For helical-groove seal, however, the leakage shows a significant decrease with the increasing rotating speed and the roughness on stator surface can enhance the “pump effect” of helical-groove. The static and rotordynamic characteristics of annular seals with cryogenic liquid oxygen are limited in the previous literature. To make use of the advantages of both types of seals and address the sealing challenge in liquid oxygen turbopump, three types of liquid annular seals were designed for the front shoulder seal of a liquid oxygen turbopump, which include a hole-pattern seal (HPS), a double helical-groove seal (DHG), and a hybrid damper seal (HDS, with hole-pattern on stator and helical-groove on rotor). Computational fluid dynamics (CFD), as an important method to solve fluid dynamic problems, has been widely used to solve fluid governing equations. To assess and compare the leakage and rotordynamic characteristics of the present three types of annular seals under the liquid oxygen medium, a steady three-dimensional CFD method was developed to predict the seal leakage, based on the Frozen Rotor interface model. A transient three-dimensional CFD-based perturbation method was also proposed to predict the seal rotordynamic characteristics, based on the subdomain method, mesh deformation technique, and multiple-frequency elliptical-orbit whirling model. The accuracy and reliability of the present numerical methods were demonstrated based on the experimental data of leakage rates and rotordynamic coefficients for an experimental hole-pattern seal and an experimental helical-groove seal using water as working fluid. The leakage rate and rotordynamic coefficients of these three types of annular seals were calculated and compared under six variable load-operating conditions of a liquid oxygen turbopump, focusing on the seal leakage rate, effective stiffness, and damping. The numerical results show that compared with the traditional hole-pattern seal and helical-groove seal, the novel hybrid damper seal possesses the much less leakage flow rate and much better rotordynamic characteristics, so is a desired seal scheme for the impeller shoulder seal.

Tribological Behaviour of an Automotive Brake Pad System Under Los Angeles City Traffic Test Conditions

<div class="section abstract"><div class="htmlview paragraph">The Los Angeles City Traffic (LACT) brake test is well known acclaimed procedure used by many vehicle manufacturers to assess the brake pad wear behavior and to investigate the Noise, Vibration and Harness (NVH) performance of the brake system. The LACT driving route consists of a set of real-world driving conditions, which has been considered representative of the US passenger vehicle market.</div><div class="htmlview paragraph">The scope of this study is to mimic the LACT test using finite element analysis (FEA) to calculate the wear displacement based on Rhee’s theory. The Leading-edge and trailing edge of the brake pad’s wear tendency is also predicted from the simulation. The finite element model for wear simulation consists of brake system viz., Rotor, Knuckle, Pads, Anchor bracket, Piston, and Caliper. Various braking scenarios consist of different driving characteristics (Number of brake applications, vehicle speed, brake pressure, rotor temperature, and brake rotor interface friction variation) based on LACT Route traffics are replicated in FEA.</div><div class="htmlview paragraph">The wear displacement results from the finite element analysis are in good agreement with physical test results. Further, based on the wear displacement values, the brake pad’s life span is calculated and correlated well with the test measurements.</div></div>

Study on wear analysis of substitute automotive brake pad materials

ABSTRACT The objective of this work is to study the wear analysis of brake pad in braking operation to estimate the weight loss and wear rate of different bake pad materials used in automotive applications. The braking system’s in an automotive slow down or stop the automobile entirely by transforming its kinetic energy to heat energy. During breaking due to rapid interaction between the pad and rotor interface generates high temperatures, hence the brake pad must absorb heat rapidly to survive at high temperatures with no wear. This work investigates and deliberates innumerable environment-friendly and healthy substitute materials to asbestos. Generally brake pad friction substance is made of different materials such as binders, filler content, additives and reinforcements, to satisfy the specifications and adjust their percentage effects on the wear properties. Over the previous few years, the brake pads have been manufactured of asbestos material with enough electrical, tribological as well as physical properties, but that causes cancer and many other health issues, and therefore its use is redundant. In this work three specific mixtures are used with adjusted ratios of ingredients and observed their impact on the tribological characteristics. More weight loss (8–10%) is observed for the asbestos material as compared to the non-asbestos material. The wear rate increases with increase in contact pressure between the brake surfaces under dry condition. As the wear rate of non-asbestos material and CL3003 material is less as compared to asbestos, hence these can be a good option for the replacement to asbestos.

Improving the Film Cooling of a Rotor Blade Platform

This paper shows the results of an experimental activity developed in cooperation between Ansaldo Energia and the Department of Engineering and Applied Science of Bergamo University with the aim of assessing the impact of newly designed holes on the thermal protection of a rotor blade platform. The original rotor blade platform featured ten cylindrical holes located along the blade pressure side (PS). Moreover, the channel front side was cooled exploiting the seal purge flow exiting the stator to rotor interface gap. The front midchannel, and particularly the region around the interplatform gap, remained uncooled. To protect this region, two sets of cylindrical holes were designed and manufactured on a seven blade cascade model for experimental verification. Aerodynamic and thermal tests were carried out at low Mach number. To evaluate the interaction of injected flow with secondary flows a five hole probe was traversed downstream of the trailing edge plane. The thermal behavior was analyzed by using thermochromic liquid crystals technique, so to obtain film cooling effectiveness distributions. The seven-hole configuration coupled with a low blowing ratio of about 1.0 provided the best thermal protection without any impact on the aerodynamic performance.

Computational Simulation of Deposition in a Cooled High-Pressure Turbine Stage With Hot Streaks

Ash particle deposition in a high-pressure turbine stage was numerically investigated using steady Reynolds-averaged Navier-Stokes (RANS) and unsteady Reynolds-averaged Navie-Stokes (URANS) methods. An inlet temperature profile consisting of Gaussian nonuniformities (hot streaks) was imposed on the vanes, with vane cooling simulated using a constant vane wall temperature. The steady case utilized a mixing plane at the vane–rotor interface, while a sliding mesh was used for the unsteady case. Corrected speed and mass flow were matched to an experiment involving the same geometry, so that the flow solution could be validated against measurements. Particles ranging from 1 to 65 μm were introduced into the vane domain, and tracked using an Eulerian–Lagrangian tracking model. A novel particle rebound and deposition model was employed to determine particles' stick/bounce behavior upon impact with a surface. Predicted impact and capture distributions for different diameters were compared between the steady and unsteady methods, highlighting effects from the circumferential averaging of the mixing plane. The mixing plane simulation was found to generally under predict impact and capture efficiencies compared with the unsteady calculation, as well as under predict particle temperature upon impact with the blade surface. Quantitative impact and capture efficiency trends with the Stokes number are discussed for both the vane and blade, with companion qualitative distributions for the different Stokes regimes.

Computational Fluid Dynamics and Thermal Analysis of Leaf Seals for Aero-engine Application

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aero-engine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf–rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behavior (thermal runaway). In this paper, we use computational fluid dynamics (CFD), finite element (FE) thermal analysis, and experimental data to characterize the thermal behavior of leaf seals. This sets the basis for a study of the coupled thermomechanical behavior. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact, and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient (HTC) at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match the predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.

Numerical Modeling of the Flow Inside a Centrifugal Pump: Influence of Impeller–Volute Interaction on Velocity and Pressure Fields

To analyze the centrifugal pump NS32 using numerical model and predicting the performance of a fluid flow in complexes geometry, we conduct several numerical simulation with different turbulence models. To evaluate the effect of turbulence model on the flow characteristics, the k-\({\varepsilon}\), SST and SST-CC turbulence models were tested. The simulations have been made using the multiple reference frames (MRF) technique to take into account the impeller–volute interaction. The computational domain is composed of two parts, a stator (volute) and a rotor (impeller). The impeller–volute interaction has been simulated using the frozen–rotor interface model for the steady-state calculations and the Rotor–Stator model for the unsteady ones. The distributions of velocity and pressure are computed using the Reynolds-Averaged Navier Stokes approach for a wide range of operating flow rates. To analyze the internal flow, simulation was carried out for several relative positions between the impeller blades and the volute tongue. In fact, the pressure fluctuations were numerically measured at five locations along the impeller and compared to experimental measurements. In addition, the unsteady pressure head evolution versus time was followed up. Then, an experimental validation of global and local characteristics of the pump was carried out.

Steady dynamical behaviors of novel viscous pump with groove under the rotor

A novel viscous pump with groove under the rotor in straight channel is first analyzed, and associated flow dynamic behaviors and characteristics are numerically investigated by 2-D laminar model. As Reynolds number rises, the vortices near the rotor become asymmetrical and larger, and then the dimensionless flow flux drops, while the dimensionless driving power rises. The groove height can also play an important role in the dynamical performance of the viscous pump. As the groove height increases, the dimensionless flow flux will first increase and then decrease, and it reaches maximum with optimal groove height. For small groove height, the flow passage with positive x-velocity is extended near the rotor, so the flow flux increases with groove height. For large groove height, the vortices in the upstream and downstream regions can combine into one large vortex, and the flow flux is obviously reduced. The driving power also affects the dynamic performance of viscous pump, and it is dependent upon the wall shear stresses at the rotor interface. In the narrow gap between the groove and rotor, thin film flow exists, so the wall shear stresses adjacent to the groove are much larger than those away from the groove, and the shear stresses will reach maximum near the groove edge. As a result, the dimensionless driving power of rotor will increase with the groove height but decrease with the gap width.

산업용 원심블로어 수치해석을 위한 수치모델 평가

The present study represents the effects of boundary condition on the performance of a centrifugal blower at the interference plane between rotational and stationary domains using three dimensional compressible Navier-Stocks equations. Two boundary conditions, frozen-rotor and stage, are compared to analyze the blower performance. Installation angle between the cutoff of a volute casing and a impeller blade is also introduced to evaluate the blower performance and to understand the internal flow inside the blower. Throughout numerical simulation, it is found that the frozen rotor interface method at the interference plane represents well the variations of flow field inside the blower compared to stage interface method. However, pressure has maximum two percent error according to the installation angles while pressure is almost constant for the stage interface method. And stage interface method can relatively well predict the blower performance. Detailed internal flows of the centrifugal blower are compared and analyzed by numerical simulation.

Gradient Design Model of Contact Interface for Ultrasonic Motor

Ultrasonic motor is a new type of motor driven by friction force between the contact interface of rotor and stator. Friction material is an important part of contact interface. Its design and wear control are key problems for ultrasonic motor. A simplified model of ultrasonic motor is established. Effect of wear of friction material on contact parameters and driving friction force is studied. The properties that worn friction material should have are obtained by keeping stable contact width between rotor and stator. Design principle and theoretical structure model of gradient friction material for ultrasonic motor are proposed. The simulation analysis shows that normal elastic modulus of friction material pasted on rotor should gradually decline from the extenior to the interior. This type of friction material can maintain the output properties and increase performance lifetime of ultrasonic motor. And a new field is opened up for choosing and reasearching friction material for ultrasonic motor.

Rotational feedthrough using an ultrasonic motor and its performance in ultra high vacuum conditions

Ultrasonic motor is one of the promising actuators that are utilized in ultra-high vacuum (UHV) conditions. The authors have proposed a rotational feedthrough for UHV using a mode-rotational type ultrasonic motor. This rotational feedthrough is distinguished by its arrangement of driving parts. The piezoelectric ceramics and wiring parts were arranged outside the vacuum chamber because they can be source of outgases. Previously the authors have just proposed this idea and reported on the successful operation in vacuum, although the output torque and duration of operation were insufficient for such applications as positioning tables. In this study, the stator transducer was redesigned for larger output torque and stator–rotor interface materials were modified from combination of metal–ceramic to metal–plastic. As a result, output torque and duration of operation were improved by factors of 4 and 20, respectively; 22 mN m and 27 h. In addition, baking treatment was carried out and an UHV of 3×10 −7 Pa was achieved.

Optimization of travelling wave ultrasonic motors using a three-dimensional analysis of the contact mechanism at the stator–rotor interface

The present paper investigates optimization rules and new design methodologies dealing with the contact mechanics in rotative travelling wave ultrasonic motors (TWUM). The proposed approaches focus on the design of the rotor, including the friction layer that is usually deposited onto its lower surface, while the stator is supposed to be preliminary designed. Contact aspects such as the transmission of mechanical power as well as the wear mechanism of the friction layer are investigated, according to the analysis of the stator–rotor contact mechanics in both hoop and radial directions. Considering a classical wear criterion in a preliminary step, a contact ratio, that allows the mechanical power to be optimized, is pointed out in the hoop direction. In a further step, the contact conditions in the radial direction are improved through the elastic fitting of the stator and rotor radial deflexions, therefore allowing the material's wear to be decreased. Some experimental tests, that have been recently performed, give a comparison of wear marks, which occur onto optimal and non-optimal rotor geometries. A first mechanism synthesis is finally proposed in such a way to allow the mechanical architecture of the rotor (including the friction layer) to be automatically designed according to a given set of mechanical constraints.

An Iterative CFD and Mechanical Brush Seal Model and Comparison With Experimental Results

The position of the bristles within a brush seal is dictated by the pressure distribution within the seal, which is itself influenced by the position of the bristle matrix. In order to predict mass flows, pressure capabilities, bristle displacements, stresses, and contact loads at the rotor interface, a technique for iterating between a CFD and a mechanical model has been developed. The iterative technique is used to model the behavior of seals with an initial build clearance, where the application of pressure causes a change in the position of the bristle matrix. Frictional effects between neighboring bristles and at the backing ring influence the behavior of the bristles and these are accounted for within the mechanical part of the model. Results are presented and discussed for seals of both initial build clearance and interference. The mathematical predictions for flow, contact loads at the rotor interface, and the nature of the bristles displacements are compared with experimental results.

Improved transient fault simulation on a laboratory model of a turbine-generator

In order to enable a simulated fault current in the region of 4000 A to produce a pulsating magnetisation in the stator coil, an arrangement of a parallel tuned-circuit was constructed. The performance characteristics of the tuned-circuit were assessed from an analytical solution (Transient response method) and modelling on an Apollo computer using the transient response package. The inrush current which is associated with the starting of the tuned-circuit was controlled with a soft-start, which increased the input voltage across the coil from zero to full preset value in 50 cycles. The soft-start circuit consisted of two anti-parallel thyristors, current-limiting resistor, phase-angle trigger unit and its control circuitry. Spurious triggering of the thyristor was greatly reduced by placing the current-limiting resistor in between the supply and the thyristor. The possible causes are discussed. A detailed comparison of the measured flux for the fault current of 4000A at an air-gap of 75 mm, for conditions with and without the endbell, at the end of the rotor suggests that the conduction current is dependent on the contact resistance at the endbell and rotor interface.