Stator Disk Research Articles

Effect of Purge on Secondary Flows in Turbine Due to Interaction Between Cavity Flow and Main Channel

Nowadays, a lot of efforts are being made to increase turbine inlet temperatures (TIT), with the aim of increasing efficiency in aircraft and power generation turbines. Due to the higher temperature level, advanced cooling solutions to preserve material durability are necessary. It is essential to avoid contact between hot gases and the temperature-sensitive components, such as the stator and rotor cavity disks. Modern gas turbine performance optimization centers on reducing leakage and refining sealing systems. The interaction between the main flow and cavity flow in stator/rotor systems has a significant role in loss generation. This study employs Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations to investigate the unsteady interactions within the stator/rotor cavity of a low-pressure turbine. Numerical results are compared and validated against experimental data obtained in the cavity rig of the University of Genova. The research focuses on the effects of stator/rotor interactions, including wake ingestion from upstream rotor bars and the blocking influence of downstream potential effects on cavity sealing effectiveness. In this paper, a comparison between the zero cooling air flow rate and cavity sealing condition is shown. Special attention is given to unsteady loss mechanisms occurring downstream of the vane row and in areas where the cavity flow re-enters the main channel, showing how cooling flow rates affect these losses. From this study, it can be seen that by increasing the cooling flow rate injected into the cavity, there is an increase in the hub’s passage vortex effect and there is a more intense interaction between the main flow and the cavity flow. These results offer valuable insights into the mechanisms of interaction between the main flow and cavity flow.

Non-Contact Multi-Degree-of-Freedom Motor Based on Hybrid Electromagnetic-Piezoelectric Drive Mode

A new non-contact ultrasonic motor consisting of a Langevin transducer, an electromagnetic device, and a spherical rotor is presented, and the designed motor is theoretically analysis and experimentally verified. The designed motor is driven by a mixture of near-field acoustic levitation and electromagnetism, and the electromagnetic platform is controlled by three stacked piezoelectric actuators to control the deflection direction, thus driving the spherical rotor to achieve the same angle of deflection and self-propagation. By exciting the Langevin transducer under the rotor, the high-frequency vibration of the stator disc causes the air between the stator disc and the rotor to be squeezed periodically, and when the air pressure in the gap is larger than the external atmospheric pressure, the levitation force generated by the stator is larger than the gravity of the rotor, thus levitating the rotor, and when the rotor deflects, it can still achieve stable levitation because of its special geometry. The proposed new motor is expected to be used in applications requiring high output torque and micro-displacement.

Advanced Modeling of Flow and Heat Transfer in Rotating Disk Cavities Using Open-Source Computational Fluid Dynamics

Abstract Code_Saturne, an open-source computational fluid dynamics (CFD) code, has been applied to a range of problems related to turbomachinery internal air systems. These include a closed rotor–stator disk cavity, a co-rotating disk cavity with radial outflow and a co-rotating disk cavity with axial throughflow. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations and large eddy simulations (LES) are compared with experimental data and previous direct numerical simulation and LES results. The results demonstrate Code_Saturne's capabilities for predicting flow and heat transfer inside rotating disk cavities. The Boussinesq approximation was implemented for modeling centrifugally buoyant flow and heat transfer in the rotating cavity with axial throughflow. This is validated using recent experimental data and CFD results. Good agreement is found between LES and RANS modeling in some cases, but for the axial throughflow cases, advantages of LES compared to URANS are significant for a high Reynolds number condition. The wall-modeled large eddy simulation (WMLES) method is recommended for balancing computational accuracy and cost in engineering applications.

INFLUENCE OF THE PATTERN OF THE COMBINED GRINDING SET OF THE DISC MILL ON INDIVIDUAL PAPER-FORMING PROPERTIES OF FIBROUS SEMI-FINISHED PRODUCTS AND THE PHYSICAL AND MECHANICAL CHARACTERISTICS OF THE FINISHED PRODUCT

The improvement of the process of grinding fibrous semi-finished products in pulp and paper production is caused by a reduction in the raw material base, requirements for the quality of finished products, as well as the desire to reduce production energy costs. Changing the grinding parameters allows you to change the properties and characteristics of the resulting materials in a wide range. The main controlled parameters of the grinding process are the gap between the rotor and stator disks, the rotor speed, the concentration of the fibrous mass. One of the important parameters of the grinding process is also the design of the grinding set. The article considers the influence of various configurations of cavities of the combined grinding set of a disc mill on the properties of the fibrous mass and finished paper castings. Individual paper-forming properties were evaluated, including the increase in the degree of grinding of the fibrous mass and the length of the fiber, as well as the physical and mechanical characteristics of the finished castings, which include the breaking length of the paper, the number of double folds and the tear resistance index. The grinding was carried out on a semi-industrial disc mill using a combined grinding set. For comparison, wavy and conical grinding cavities with straight unidirectional knives were selected. It was revealed that the wave-shaped grinding cavity has higher quality indicators in comparison with the conical grinding cavity by the nature of the impact on the fibrous mass.

Experimental and Numerical Investigations into the Effects of Rim Seal Structure on Endwall Film Cooling and Flow Field Characteristics

During the practical operation of gas turbines, relatively cooled air from the compressor and the rim seal is applied in order to prevent mainstream ingestion into the space between the rotor and stator disc cavities, which can prolong the service life of hot components. On the one hand, the purge flow from the rim seal will inevitably interact with the mainstream and result in secondary flow on the endwall. On the other hand, it can also provide an additional cooling effect. In this paper, four rim seal structures, including an original single-tooth seal (ORI), a double-tooth seal (DS), a single-tooth seal with an adverse direction of the coolant purge flow and mainstream (AS) and a double-tooth seal with an adverse direction of the coolant purge flow and mainstream (ASDS), are experimentally and numerically investigated with mass flow ratios of 0.5%, 1.0% and 1.5%. The flow orientation of the coolant from the rim seal is considered as one of the main factors. The pressure-sensitive paint technique is used to experimentally measure the film cooling effectiveness on the endwall, and flow field analysis is conducted via numerical simulations. The results show that the cooling effect decreases in the cases of DS and ASDS. AS and ASDS can achieve a better film cooling performance, especially under a higher mass flow ratio. Furthermore, the structural changes in the rim seal have little impact on the aerodynamic performance. AS and ASDS can both achieve a better aerodynamic and film cooling performance.

Dimensionless analysis of flow and heat transfer characteristics in a high-speed rotor–stator disk cavity based on similarity criteria

Dimensionless analysis of flow and heat transfer characteristics in a high-speed rotor–stator disk cavity based on similarity criteria

Large-eddy simulation of non-isothermal flow and heat transfer in an enclosed rotor–stator cavity

This paper presents a numerical study of non-isothermal flow and heat transfer in an enclosed rotor–stator disk cavity. Wall-resolved large-eddy simulation is implemented with attention focused on the Reynolds number effect (Reϕ=105 and 5×105) and non-isothermal effects, including different thermal Rossby numbers (βΔT=0.05–0.25) and heat convection types (axial heat convection, axial and radial heat convection). Verification and validation are implemented by comparing with available experimental data and examining the resolution of the present LES. Although the Batchelor flow type is unchanged, the non-isothermal effect is found to be responsible for the acceleration of flow in both disk boundary layers and cavity core. Temperature in the cavity is negatively correlated with the Rayleigh number. The radial inward temperature gradient is found to be responsible for destabilizing the flow near the cylinders, due to the effect of centrifugal buoyant force. Transition from laminar to turbulent is shown in the rotor boundary layer for Reϕ=5×105 conditions. The non-isothermal effect increases flow unsteadiness in both rotor and stator boundary layers, but it has little to no effect on the transition position, as well as the kinematic and thermal boundary layer thicknesses, which are mainly controlled by Reϕ. Spectral proper orthogonal decomposition is implemented to explore the Reynolds number effect. Analyzing the most energetic mode and its energy spectra provides some insights into the understanding of non-isothermal rotor–stator disk cavity flows.

Large Eddy Simulation of Externally Induced Ingress about an Axial Seal by Stator Vanes

Turbine inlet temperatures in advanced gas turbines could be as high as 2000 °C. To prevent ingress of this hot gas into the wheelspace between the stator and rotor disks, whose metals can only handle temperatures up to 850 °C, rim seals and sealing flows are used. This study examines the abilities of large eddy simulation (LES) based on the WALE subgrid model and Reynolds-averaged Navier–Stokes (RANS) based on the SST model in predicting ingress in a rotor–stator configuration with vanes but no blades, a configuration with experimental data for validation. Results were obtained for an operating condition, where the ratio of the external Reynolds number to the rotational Reynolds number is 0.538. At this operating condition, both LES and RANS were found to correctly predict the coefficient of pressure, Cp, located downstream of the vanes and upstream of the seal, but only LES was able to correctly predict the sealing effectiveness. This shows Cp by itself is inadequate in quantifying externally induced ingress. RANS was unable to predict the sealing effectiveness because it significantly under predicted the pressure drop in the hot gas path along the axial direction, especially about the seal region. This affected the pressure difference across the seal in the radial direction, which ultimately drives ingress.

A Novel Axial High-Temperature Superconducting Magnetic Bearing With Simple Structure and Large Suspension Force

In this paper, we propose a novel axial high temperature superconducting magnetic bearing (HTSMB) which is used in the field of shaftless magnetic levitation flywheel. The permanent magnet (PM) rotor of the HTSMB is assembled with Halbach PM rings and a polymagnet yoke disc, and HTS bulks are equally distributed in a circle on the stator disk. Firstly, the structure of the novel axial HTSMB is proposed, and the potential advantage is introduced. Secondly, the suspension characteristic of a HTS bulk is simulated based on COMSOL Multiphysics interface of Magnetic Field, No Current (mfnc), Magnetic Field Formula (mfh), and Moving Mesh (ale), and it is verified by experiments. On this basis, the specific structure and size of the HTSMB are optimally designed by using ANSYS Maxwell. Then, the HTSMB is processed and assembled, a general method for assembling the PM rotor is introduced in detail. Finally, the suspension characteristic of the HTSMB is experimentally studied. The experimental results show that the HTSMB has more advantages in axial suspension characteristics and material cost.

Large Eddy Simulation of Rotationally Induced Ingress and Egress around an Axial Seal between Rotor and Stator Disks

In gas turbines, the hot gas exiting the combustor can have temperatures as high as 2000 °C, and some of this hot gas enter into the space between the stator and rotor disks (wheelspace). Since the entering hot gas could damage the disks, its ingestion must be minimized. This is carried out by rim seals and by introducing a cooler flow from the compressor (sealing flow) into the wheelspace. Ingress and egress into rim seals are driven by the stator vanes, the rotor and its rotation, and the rotor blades. This study focuses on the ingress and egress driven by the rotor and its rotation. This is carried out by performing wall-resolved large eddy simulation (LES) around an axial seal in a rotor–stator configuration without vanes and blades. Results obtained show the mechanisms by which the rotor and its rotation induce ingress, egress, and flow trajectories. Kelvin–Helmholtz instability was found to create a wavy shear layer and displacement thickness that produces alternating regions of high and low pressures around the rotor side of the seal. Vortex shedding on the backward-facing side of the seal and its impingement on the rotor side of the seal also produces alternating regions of high and low pressures. The locations of the alternating regions of high and low pressures were found to be statistically stationary and to cause ingress to start on the rotor side of the seal. Vortex shedding and recirculating flow in the seal clearance also cause ingress by entrainment. With the effects of the rotor and its rotation on ingress and egress isolated, this study enables the effects of stator vanes and rotor blades to be assessed.

Numerical Investigations on Gas Ingestion Mechanism Based on Flow Instabilities in Rim Seal and Cooling Characteristics of Endwall in a 1.5-Stage Axial Turbine

Abstract The sealant flow and rim seal at the periphery of cavities formed between rotor and stator disks prevent the high-temperature gas from ingesting into disk cavities and reduce the use of secondary air bleeding from a compressor. The unsteady sealing performance of rim seal and the cooling characteristics of sealant flow on endwall of a 1.5-stage axial turbine are studied by solving the three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations via shear stress transfer (SST) turbulence model. Besides, mass transfer analogy is introduced to predict the sealant distribution which makes the numerical sealing effectiveness in front and aft cavities agree well with experimental data. The accuracy of the numerical method is verified. The sealing effectiveness in cavities and the flow field in rim seal clearance are analyzed, and the film cooling performance on endwall is explored. The results show that, compared with Φ0=0.0170, the area-averaged sealing effectiveness εc on stator face is increased by 19.05% when Φ0=0.500 in the front cavity, and compared with Φ0=0.0042, the area-averaged sealing effectiveness εc on stator face is increased by 9.82% when Φ0=0.096 in the aft cavity. The nonaxisymmetric pressure on the endwall near rim seal and Kelvin Helmholtz unstable vortices arise due to the circumferential velocity difference between main flow and cavity flow. The flow field in the rim seal clearance is jointly affected by these two factors. The flow pattern in the front rim seal clearance is mainly affected by unstable vortex while the flow pattern in the aft rim seal clearance depends on the circumferential pressure distribution. According to FFT, the most significant frequency of flow field variety is about 1200 Hz and 400 Hz (corresponding to two and six blades passing periods) in front and aft rim seals, respectively. The time-averaged cooling effectiveness increases with the increase of sealant flow on endwall and decreases gradually in the axial direction. The unsteady flow behavior of cooling effectiveness on endwall is also discussed in detail.

A New Interpretation of Hot Gas Ingress Through Turbine Rim Seals Influenced by Mainstream Annulus Swirl

Abstract Rim seals are fitted at the periphery of the stator and rotor disks to reduce the adverse effects of hot gas ingress on highly stressed turbine components limited by temperature. Ingress is induced by rotational effects such as disk pumping, as well as by asymmetric pressure-driven unsteady phenomena. These influences superpose to form a complex flow-physics problem that is a challenge for computational fluid dynamics. Engine designers typically use practical low-order models that require empirical validation and correlating parameters. This paper identifies the swirl ratio in the mainstream annulus as a dominant characterizing parameter to predict ingress. This is a new interpretation that is supported by extending a low-order model based on turbulent transport using an effective eddy mixing length based on the difference in swirl between the annulus and seal clearance. Experimental measurements were made using a 1.5-stage turbine rig at low Reynolds number. The influence of annulus swirl ratio was investigated over a range of flow conditions and two rim-seal geometries, with the ingress quantified using CO2 tracer concentration in the sealing flow. The concentration data were complemented by measurements in the annulus using a five-hole aerodynamic probe.

Experimental investigations on flow and heat transfer characteristics in a high-speed rotor–stator disk cavity with axial throughflow

The rotor–stator disk cavity system is of great importance for turbine blade cooling and preventing gas invasion in the aircraft engine. This study presents an experimental investigation on a high-speed rotor–stator disk cavity with axial throughflow. The aims are to experimentally measure and reveal the pressure characteristics, windage heating, swirl characteristics, and relative temperatures at a high rotational speed of 0–9000 rpm with mass flow rates of 0.05–0.15 kg/s. Especially, a new measurement idea was proposed and tested that relative temperature in the rotor system can be obtained by measuring absolute parameters in the stator system. Experiment results reveal that rotational speed and inlet mass flow are the main parameters to determine flow characteristics in the rotor–stator cavity. The increase of rotational speed will enhance the effect of centrifugal boosting, windage heating, and swirl characteristics. But increasing inlet mass flow rate will lead to the opposite effect. When the airflow is in the heat balance state, relative total temperature and adiabatic temperature can be acquired by measuring absolute temperature and swirl ratio at the same radius. The maximum deviation is below 2 K. The results can be beneficial to the optimization design of rotor–stator disk cavity in the gas turbine engines.

Design of Wireless Charging Coils for Aero-engine Telemetry Information Transmission System

Abstract In order to meet the need of non-contact transmission of aero-engine telemetry information, first of all, a rotor disk and a stator disk suitable for near field communication are designed in this paper, then, the coil design of wireless charging system suitable for high centrifugal force load is carried out. The designed single charging coil can charge two receiving coils at the same time. In order to eliminate the influence of aluminum alloy rotor disk and stator disk on charging performance, concave ferrite slots are installed on rotor disk and stator disk respectively to shield charging coil and receiving coil. The designed charging coils are fabricated and integrated with rotor disk and stator disk respectively. Finally, the designed charging coil and receiving coils are connected into the charging system for testing. The test results show that the charging coil and receiving coils are completely matched with the charging circuit and receiving circuit, and their performance can fully meet the use requirements of aeroengine telemetry information transmission system.

Design of Transmitting Antenna for Aero-engine Telemetry Information Transmission System

Abstract The demand of aero-engine for non-contact telemetry information transmission is very urgent. Based on the analysis of the characteristics of aero-engine telemetry information transmission system, the rotor disk and stator disk suitable for near-field communication under high centrifugal load are designed in this paper. In order to ensure the stable transmission of telemetry information under large angular displacement between rotor disk and stator disk, two circular arc-shaped dipole antennas are designed to be symmetrically installed on rotor disk for telemetry information transmission. The designed pair of arc-shaped dipole antennas are fabricated and measured. The measurement results show that the two transmitting antennas resonate at 2.19GHz and 2.27GHz respectively, and their impedance bandwidth of -10dB is 35MHz and 34mhz respectively. In their operating frequency band, the isolation between them is greater than 38dB, and their performance fully meets the needs of aeroengine telemetry information transmission.

Numerical simulation analysis of flow characteristics in the cavity of the rotor-stator system

ABSTRACT Investigating the flow characteristics in the cavity by changing the rotor profile of the rotor-stator system is of considerable significance, this paper simplifies clearance flow to rotor-stator cavity flow. The numerical simulation results are compared with the experimental results of the windage torque of the rotor-stator system, and the results show that the accuracy of the numerical calculation meets the requirements. The inlet flow rate and outlet gap were unchanged, and the flow in the concave cavity was most similar to the original model. The torque increased slightly and was more entrained, while the flow pattern of the convex cavity was more chaotic, and various forms of vortices appeared in the rotor boundary layer. The interference of the rotor and stator disks and the viscous effect of the fluid in the cavity are the main reasons for the generation of torque, and the Reynolds stress near the rotor wall also contributes partly to the torque. After data processing, an interesting phenomenon was observed. In the boundary layer of the rotor, the radial flow in which the inertial force plays a major role is transformed into a circular motion dominated by the rotation of the rotor.

Influence of imperfections on the stability of a multi-disc friction system

This paper studies the impact of geometrical imperfections (gaps in the links, center distance, inclination angle, etc.) on the stability and the dynamic behavior of mechanical systems exhibiting friction-induced vibrations (braking systems, clutches, etc.). It comes further to two papers relating to improved modeling of friction and separation at the interface of a rotor-stator system. The latter is a phenomenological model which is composed of an embedded beam on which a disc is mounted, called the stator, in contact with another disc called the rotor. The phenomenological mechanical system used in this paper is a new version of the latter model taking into account some of the geometrical imperfections present in real mechanical systems. In the proposed model, the rotor and stator discs have the ability to move radially thanks to the gaps in the links. The inclination angle of the rotor disc and a center distance between the stator and the rotor discs are also introduced. The inclusion of these three geometrical imperfections induces additional complex phenomena that have a strong impact on the stability and dynamic behavior of the mechanical system, because the coupling of the imperfections with the rotor rotation gives rise to a non-autonomous dynamical system. Consequently, stability studies of fixed points must be replaced by stability studies of periodic orbits involving the construction of a monodromy matrix. In conclusion, significant differences in the values of the bifurcation point and the levels of the associated instabilities can be observed, unlike in a study that does not take geometrical imperfections into account. • Modeling of geometric imperfections in a system presenting vibratory instabilities induced by friction • Influence of the coupling of imperfections with the rotation on the stability and the dynamic behavior • Coupling implies replacing fixed point stability studies by orbital stability studies

Flow instability effects related to purge through a gas turbine chute seal

This paper investigates flow instabilities inside the cavity formed between the stator and rotor disks of a high-speed turbine rig. The cavity rim seal is of chute seal design. The influence of flow coefficient on the sealing effectiveness at constant purge flow rate through the wheel-space is determined. The effectiveness at different radial positions over a range of purge flow conditions and flow coefficients is also studied. Unsteady pressure measurements have identified the frequency of instabilities that form within the rim seal, phenomena which have been observed in other studies. Frequencies of these disturbances, and their correlation in the circumferential direction have determined the strength and speed of rotation of the instabilities within the cavity. Large scale unsteady rotational structures have been identified, which show similarity to previous studies. These disturbances have been found to be weakly dependent on the purge flow and flow coefficients, although an increased purge reduced both the intensity and speed of rotation of the instabilities. Additionally, certain uncorrelated disturbances have been found to be inconsistent (discontinuous) with pitchwise variation.

Experimental Results of Local Shear Stresses and Friction Torque in an Open Rotor-Stator Disk System

Abstract This contribution presents experimental investigations of friction torque in an open rotor–stator disk system by using two different measuring procedures. The first procedure is based on a thermo electrical wall shear stress sensor. The sensor is investigated in two different substrates and different measuring parameters. A thermal model consisting of the supplied heating power, the thermal resistance toward the fluid, and into the substrate as well as the over temperature is used to achieve the heat transfer coefficient on the sensor surface. This heat transfer coefficient is attributed by a functional relationship to the wall shear stress. This relationship is first calibrated in a rectangular channel and subsequently validated at a fully turbulent flat plat flow. The second measuring procedure based on the tangential displacement of the stator disk due the friction torque. The disk is attached at a torsion spring. The friction torque is achieved by the torsion spring constant and the tangential displacement of the stator disk. Both measuring procedures are compared and agree well with each other. The used test rig has the possibility of reaching rotational Reynolds numbers representative, for instance, of a modern gas turbine. The investigations were carried out by a 0.5 m diameter rotor disk rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04. The friction torque is measured on the stator disk and can be converted into moment coefficient. Moment coefficient on stator and measured pressure distributions are presented for different gap ratios and rotational Reynolds number.

Large-Eddy Simulations of Rim Seal Flow in a One-Stage Axial Turbine

The flow field in a one-stage axial flow turbine with 30 stator and 62 rotor blades including the wheel space is investigated by large-eddy simulation (LES). The Navier-Stokes equations are solved using a massively parallel finite-volume solver based on a Cartesian mesh with immersed boundaries. The strict conservation of mass, momentum, and energy is ensured by an efficient cut-cell/level-set ansatz, where a separate level-set solver describes the motion of the rotor. Both solvers use individual subsets of a shared Cartesian mesh, which they can adapt independently. The focus of the analysis is on the flow field inside the rotor stator cavity between the stator and rotor disks. Two cooling gas mass flow rates are investigated for the same rim seal geometry. First, the time averaged flow field for both simulations is compared, followed by a detailed investigation of the unsteady flow field. The results for the cooling effectiveness are compared to experimental data. Both cases show good agreement with experimental data. It is shown that for the lower cooling gas mass flux several of the wheel space’s acoustic waves are excited. This is not observed for the higher cooling gas mass flux. The excited waves lead to stable, i.e., bounded, fluctuations inside the wheel space and result in a significantly higher hot gas ingestion.