Turbine Rotor Disk Research Articles

Determination of hydrogen influence on microhardness and microstructure characteristics of aviation alloys

This paper presents results of the studies of hydrogen exposure duration influence on the characteristics of two aviation alloys at atmospheric pressure and room temperature. First alloy (alloy 1) was obtained by hot isostatic pressing, and was used for the manufacture of gas turbine rotor discs. Second alloy (alloy 2) was obtained by directional crystallization, and was used for the manufacture of gas turbine blades. It was determined that microhardness of the samples increased during 1000 h of hydrogen exposure duration. The relative increase of the microhardness was insignificant, and for the sample of alloy 1 it was 2.5 %, and for the sample of alloy 2 – 2 %. Correlation analysis of the XRD diagram parameters indicated positive and negative statistically significant relationships correlation between XRD diagrams peaks parameters, hydrogen exposure duration and microhardness of the samples. It was revealed that XRD diagrams peaks of alloy 1 were broadened and their heights increased during hydrogenation, which can be associated with a decrease of dislocations in the grains and their local accumulation at the grains boundaries. Conterwise, XRD diagrams peaks of alloy 2 were narrowed, which can indicate an increase of dislocations in the material grain structure. XRD diagrams processing demonstrated that the crystallite size and dislocation density for alloy 1 decreased with a delay from the hydrogenation start, but for alloy 2 these parameters monotonically increased, and it corresponds to microhardness changes trends of the samples during hydrogenation.

On the role of plastic relaxation in stress assisted grain boundary oxidation

The influence of plasticity on the high-temperature stress-assisted grain boundary oxidation of nickel-based superalloys used in applications such as turbine rotor discs is investigated using the method of discrete dislocation plasticity (DDP). The misfit stress fields of nib-shaped intrusions are captured by a continuous distribution of edge dislocations whose extra half planes represent the volumetric misfit of the oxide, which is implemented in a planar formulation of DDP by invoking the linear superposition principle. DDP simulations show that stresses generated by an intrusion several microns or more in size are large enough to generate dislocation pileups with associated stresses at the intrusion interface on the order of 1 GPa, which in turn lead to localized growth and morphology change of the intrusion by stress-assisted diffusion. This morphology change relaxes the compression stress inside the intrusion near the base, and therefore increases the fracture resistances of the intrusion. The effects of applied loading and background plasticity on the growth rate of the intrusion in defect-free and prestrained samples are predicted. It is found that applied tensile stress generally increases grain boundary oxidation, while in prestrained samples the enhancement of the intrusion growth rate by the applied load is insignificant due to dislocation pile-ups ahead of the oxidation process.

Investigation Mechanical and Microstructural Behavior of Operated and Unoperated Turbine Rotor Discs

In gas turbine engines, turbine sections are exposed to high temperature and loads during operation and therefore turbine inlet boundary is considered the most challenging for turbomachines. Ni-based super-alloys are used for turbine materials in gas turbine engines because of their superior mechanical characteristics at high temperatures. In this research, two Mar M-247 polycrystalline cast Ni-based turbine rotors, which were operated and non-operated in turbojet engine tests, had the same design and applied the same two-step aging heat treatment, were examined microstructurally and mechanically. As a result of the mechanical analysis, it was observed that the tensile strength (Rm (P): 537Mpa; Rm (G): 590 Mpa) ductility, and hardness (429 HV (P), 440 HV (G)) of the operated turbine rotor increased. In the microstructure analysis, blocky and Chinese script-like carbides and gamma prime eutectic islands were found in both turbine structures. EDS analysis showed that the carbides in the matrix are rich in Hf, Ta, and Ti, and the grain boundary carbides are rich in Cr and W.

Design and Finite Element Analysis (FEA) of Gas Turbine Rotor Disc

Abstract: A Turbine wheel (rotor) plays a significant role in gas turbine. The rotor on which the blades are mounted transmitting this motion holds a key point to better efficiency of gas turbine. Thus, more focus should be given to the design of the turbine rotor. Gas-turbine discs are normally operated at high temperatures. The hot gases contact the blades and the rim of the turbine rotor and thus maintain the rim at high temperature. The temperature gradient at rim and central portion of rotor causes the sources for thermal stresses. The disc is expected to perform well despite all the stringent operating conditions. The Advancement in gas turbine materials has been always a major concern—higher their capability to with stand elevated temperature service, produce lower stresses, light weight and more the engine efficiency. In this thesis, an attempt is made to determine the stresses like Thermal, Structural, Radial, and other stresses with different materials.

Aerothermal performances of a rotating turbine disk cavity with non-uniform wall temperature profiles in an aero-engine

Aerothermal performances of a rotating turbine disk cavity with non-uniform wall temperature profiles in an aero-engine

Vertical wake deflection for floating wind turbines by differential ballast control

Abstract. This paper presents a feasibility analysis of vertical wake steering for floating turbines by differential ballast control. This new concept is based on the idea of pitching the floater with respect to the water surface, thereby achieving a desired tilt of the turbine rotor disk. The pitch attitude is controlled by moving water ballast among the columns of the floater. This study considers the application of differential ballast control to a conceptual 10 MW wind turbine installed on two platforms, differing in size, weight, and geometry. The analysis considers the following: (a) the aerodynamic effects caused by rotor tilt on the power capture of the wake-steering turbine and at various downstream distances in its wake; (b) the effects of tilting on fatigue and ultimate loads, limitedly to one of the two turbine-platform layouts; and (c) for both configurations, the necessary amount of water movement, the time to achieve a desired attitude, and the associated energy expenditure. Results indicate that – in accordance with previous research – steering the wake towards the sea surface leads to larger power gains than steering it towards the sky. Limitedly to the structural analysis conducted on one of the turbine-platform configurations, it appears that these gains can be obtained with only minor effects on loads, assuming a cautious application of vertical steering only in benign ambient conditions. Additionally, it is found that rotor tilt can be achieved on the order of minutes for the lighter of the two configurations, with reasonable water ballast movements. Although the analysis is preliminary and limited to the specific cases considered here, results seem to suggest that the concept is not unrealistic and should be further investigated as a possible means to achieve variable tilt control for vertical wake steering in floating turbines.

Comprehensive evaluations of heat transfer performance with conjugate heat dissipation effect in high-speed rotating free-disk system of aero-engines

Thermal boundary conditions of the turbine disk cavity system are of great importance in the design of secondary air systems in aero-engines. This study aims to investigate the complex heat transfer mechanisms of a rotating turbine disk under high-speed conditions. A high-speed rotating free-disk model with Dorfman empirical solutions is developed to evaluate the heat transfer performance considering various factors. Specifically, the influence of compressibility, variable properties, and heat dissipation is determined using theoretical and numerical analyses. In particular, a novel combined solution method is proposed to simplify the complex heat transfer problem. The results indicate that the heat transfer performance of a free disk is primarily influenced by the rotating Mach number, rotating Reynolds number, Rossby number, and wall temperature ratio. The heat transfer temperature and Nusselt number of the free disk are strongly correlated with the rotating Mach number and rotating Reynolds number. Analysis reveals that heat dissipation is a critical factor affecting the accurate evaluation of the heat transfer performance of the turbine disk. Thus, the combined solution method can serve as a reference for future investigations of flow and heat transfer in high-speed rotating turbine disk cavity systems in aero-engines.

Analysis of Vertical Wind Shear Effects on Offshore Wind Energy Prediction Accuracy Applying Rotor Equivalent Wind Speed and the Relationship with Atmospheric Stability

If the wind speed that passed through a wind turbine rotor disk area is constant, the hub height wind speed (HHWS) could be representative of the wind speed over the rotor disk area. However, this assumption cannot be applied to the large wind turbine, because of the wind shear effect by atmospheric stability. This is because the hub height wind speed cannot represent the vertical wind shear effect from the aerodynamics characteristic on the wind turbine. Using SCADA and offshore LiDAR observation data of the Anholt offshore wind farm, it is investigated whether the rotor equivalent wind speed (REWS) introduced in IEC61400-12-1 can contribute to the improvement of power output forecasting accuracy. The weighted value by separated sector area and vertical wind shear effect by difference between heights can explain the role of energy flux and atmospheric stability on the exact wind energy calculation. The commercial CFD model WindSim is used to calculate power production according to the HHWS and the REWS, and to compare them with the actual AEP of the local wind farm. The classification of atmospheric stability is carried out by Richardson number, which well represents the thermal and physical properties of the atmosphere below the atmospheric boundary layer, along with the wind shear coefficient and turbulence intensity. When atmospheric stability was classified by each stability index, the REWS-based predicted power output was sometimes more accurate than HHWS, but sometimes inferior. However, in most cases, using the REWS, it was possible to calculate an estimate closer to the actual power output. Through the results of this study, it is possible to provide a rationale for which method, REWS or HHWS, can more accurately calculate the expected power output and effectively derive the economic feasibility of the project by identifying the characteristics of local atmospheric stability before the wind farm project.

Comprehensive investigations on fluid flow and heat transfer characteristics of a high-speed rotating turbine disk cavity system of aero-engine

Thermal loading management of turbine disks get important attention in the safety of aero-engines due to a large temperature level and gradient differences in the turbine disk cavity. This study conducts a comprehensive evaluation to address complex heat transfer problems in a high-speed rotating turbine disk cavity system, fully considering multiple factors. A theoretical derivation is conducted to fully elaborate the multifactor influencing mechanisms of the system based on similarity criteria and a dimensional analysis method. Notably, a high-speed rotational experimental platform of rotating disk is established to verify the research method's reasonability and the result's accuracy. Furthermore, four dimensionless operation cases are conducted to assess the correlation mechanism of the system performance with a strong rotating flow and heat transfer. The results indicate that the main correlation factors of the disk cavity system performance are the flowing Reynolds number, rotating Mach number, rotating Reynolds number, specific heat ratio, and wall temperature. Moreover, the Rossby number and the swirl ratio are used to evaluate the fluid flow characteristics. With the increase in the flowing Mach number from 0.006 to 0.15 and the rotating Reynolds number from 0.74 × 106 to 14.80 × 106 at 9000 rpm, the Nusselt number on the rotor disk wall enhances to 1639.4 and 1286.9, respectively. However, it decreases to 1001.91 for the rotating Mach numbers in the range of 1800–13,500 rpm. Particularly, the dimensionless heat flux is in the range of 0.0026–1.23 under multifactor effects. In summarizing, the present findings are of importance for improving the thermal management and performance reliability of aero-engines by developing an advanced turbine disk cooling system.

Study of dual grain microstructure heat treatment in steel specimen representing gas turbine rotor disc

Gas turbine discs which support the rotor blades operate at relatively high speeds and high rim temperatures and are therefore subjected high creep damage at the rim area and to very high low-cycle fatigue damage at the bore. Any heat treatment which results in homogenous grain structure and one small band of grain size will limit the life of the disc either by creep at the rim or by the fatigue at the bore. If the heat treatment parameters are optimized to increase the grain size at the rim area closer to the ASTM 6.5 and to finer grain size at the bore area closer to ASTM 11.5, the heat treated disc is likely to have much superior operational life as compared to that of heat treated which results in homogenous grain structure and size throughout the disc. There is therefore the need for exploring possibilities of obtaining variable grain structure during heat treatment operation.This study is aimed at evaluating two possible heat treatment processes that are likely to result in distinctly different grain size in a single test specimen such as a circular rod. These test rods represent rotating gas turbine discs and the objective of achieving differential grain size is to optimize and balance the creep life at one half portion of the test rod (representing the disc rim or Outer Diameter) and fatigue life at another half portion of the test rod(representing the bore or Inner Diameter).

Comprehensive evaluations on performance and energy consumption of pre-swirl rotor–stator system in gas turbine engines

Pre-swirl system has an indispensable role to supply enough cooling air with appropriate pressure, temperature, and mass flow rate to improve the life and the efficiency of turbine cooling blades and vanes. This study aimed to reveal the heat transfer mechanism and energy conversion characteristics of a multi-in and multi-out pre-swirl system. Subsequently, a novel modified prediction modeling was proposed to evaluate the system performance and energy conversion with complete consideration of multi-factors, especially for determining the influence of the seal flow, wall friction, work done by the rotating turbine disc, and rotor–stator moment. The results reveal that a high pre-swirl cooling performance and low-energy consumption can be obtained from the contribution of the airflow swirl ratio, whereas the swirl ratio was susceptible to the mixed seal flow. Thereafter, the seal outflow improved the system temperature-drop efficiency, whereas the seal inflow strongly influenced the heat transfer and energy consumption characteristics. The modified modeling resulted in a 56.89% increase in prediction accuracy relative to the Liu-model. Moreover, the nonlinear relationships between the seal flow and system performances can be comprehensively and accurately evaluated. In particular, a peak in a system temperature drop of 38.5 K can be realized with a low-energy consumption of −133 kW and a 64% enhancement in the air-supply flow rate based on a contribution of the seal flow on airflow swirl ratio. Thus, the implementation of the modified modeling can prove significant in theoretical guidance and engineering applications.

Theoretical and experimental evaluation of temperature drop and power consumption in a cover-plate pre-swirl system for gas turbine cooling

The pre-swirl system has the ability to decrease the air supply temperature so as to improve the cooling performance and the operating life for turbine rotating blade. In this paper, a test rig was designed to reveal the aero-thermal characteristics in a cover-plate type pre-swirl system of gas turbine engines. Then, the theoretical derivation and experimental evaluation were conducted to reveal the variation of temperature drop and power consumption of a pre-swirl system with the mass flow rate ratio and rotating speed. Especially, the pressure and temperature on the rotating turbine disc were measured by a co-rotating data recorder. The theoretical and experimental analyses indicate that the temperature drop of pre-swirl system increases as the velocity coefficient of the pre-swirl nozzle outlet enhanced, but presenting a decrease with the increment of the rotating Mach number. Then, the ideal dimensionless temperature drop can be formally unified with the actual dimensionless temperature by defining the tangential velocity recovering coefficient, which is verified with the experimental results. Moreover, a linear relationship between the dimensionless temperature drop and the effective swirl ratio at the nozzle outlet can be deduced further. Especially, this relationship shows a good agreement between the predicted values and numerical results. Since the dimensionless temperature drop decreases with the increase of the dimensionless power consumption; an important discovery can be concluded that the algebraic sum of these two physical quantities is always equal to 1. Therefore, the results can offer a reference for the design and optimization of gas turbine cover-plate type pre-swirl system.

Flow analyses of diffuser augmented wind turbines

ABSTRACT The main purpose of the study was to obtain the design parameters of optimum wind turbine linear shrouding bodies to enhance wind turbine performance further. The blade element momentum theory and k-ε turbulence model were used to determine the performance of wind turbine linear shrouds. Based on 17 different wind turbine shrouding systems considered in the present study, it is determined that the mass flow rate of the air passing through the turbine rotor disc section can be enhanced approximately by a factor of 1.85. Numerical analysis revealed that the highest wind power increase was achieved from an optimally designed linear shrouding system of the type having an inlet shrouding component at the upstream and flange component at the downstream of the diffuser. The theoretical wind turbine power coefficient, Cp indicated that power generations can be enhanced on the turbine rotor blades by a factor of 6.33. This result exceeds the field trial testing found in the literature. Finally, it is concluded that this optimally designed wind turbine inlet shroud system and flange components can be applied for micro wind turbines.

Field testing of a local wind inflow estimator and wake detector

Abstract. This paper presents the field validation of a method to estimate the local wind speed on different sectors of a turbine rotor disk. Each rotating blade is used as a scanning sensor that, traveling across the rotor disk, samples the inflow. From the local speed estimates, the method can reconstruct the vertical wind shear and detect the presence and location on an impinging wake shed by an upstream wind turbine. Shear and wake awareness have multiple uses, from turbine and farm control to monitoring and forecasting. This validation study is conducted with an experimental data set obtained with two multi-megawatt wind turbines and a hub-tall met mast. Practical and simple procedures are presented and demonstrated to correct for the possible miscalibration of sensors. Results indicate a very good correlation between the estimated vertical shear and the one measured by the met mast. Additionally, the proposed method exhibits a remarkable ability to locate and track the motion of an impinging wake on an affected rotor.

Measured and Simulated Forced Response of a Rotating Turbine Disk With Asymmetric and Cylindrical Underplatform Dampers

Abstract The dynamics of turbine blades with underplatform dampers (UPDs) is often experimentally explored by using small test rigs like two-blade models for cost and complexity reasons. In this paper, the dynamics of a large-scale academic turbine disk is measured on a special rotation test rig. Such measurements have rarely been published so far. The test rig supports speeds up to 3600 rpm and turbine disks up to a diameter of 1.2 m. The turbine disk is tested linearly as well as with asymmetric and cylindrical UPDs. The excitation forces and the excitation order are varied. The results prove the damper effectiveness by lowering resonance amplitudes. Additionally, the mistuning influence on the result depiction is discussed. The measurements are compared to simulations of the nonlinear frequency response functions (FRFs), showing good agreement.

Effect of turbine rotor disc vibration on hot gas ingestion and rotor-stator cavity flow

Gas ingestion numerical model and rotor-stator (RS) cavity model with rotor vibration are proposed to investigate the effect of rotor disc vibration on the flow characteristics in the RS cavity and gas ingestion. Results show that the sealing effectiveness at the rim seal clearance is increased due to the rotor disc vibration, and the amplitudes of the pressure fluctuation and the radial velocity of the gas ingestion flow at rim seal clearance are reduced. The speed of the Kelvin-Helmholtz vortex is approximately 82.28% of that without rotor vibration. Numerical results reveal that the effect of the rotor vibration on the RS cavity flow covers the whole cavity, the unsteady flow at the low radius region in RS cavity is caused by the vibration rotor disc. The frequency of the pressure oscillation at the low radius region is approximately equal to the vibration frequency of the rotor disc as the periodic variation of the tip clearance shape in the horizontal intake section of sealing air and the induced periodic mass flow rate of inlet sealing air. The flow characteristics in RS cavity are together determined by the rotor vibration parameters and the Kelvin-Helmholtz vortices in rim seal region.

Characterization of the nonlinear fracture resistance parameters for an aviation GTE turbine disc

AbstractThe effects of crack growth rate model formulation, based on the elastic‐plastic and undamaged/damaged creep crack tip fields on the behaviour of low‐cycle fatigue and creep fracture resistance parameter behaviour, are represented by numerical calculations. The crack growth rate models include the fracture process zone size and damage parameters. An aviation gas turbine engine (GTE) rotating turbine disc is the focus of this innovative application of basic analytical and numerical solutions. For the GTE turbine disc, the constraint parameters, local fracture process zone sizes, and nonlinear plastic (Kp) and creep (Kcr) stress intensity factors are calculated by finite element analysis to characterize the fracture resistance along the semielliptical crack front as a function of the flaw aspect ratio, operation temperature, and disc rotation speed. Predictions of the creep‐fatigue crack growth rate and residual lifetime are given for different combinations of operation loading conditions and damage of the GTE turbine disc.

Determination of crack resistance of a steam turbine rotor under the volume forces action

The problem of the crack resistance of a steam turbine rotor disk with an initial semi-elliptical crack is investigated in this paper. The forces affecting the disk are due to its rotation and consist of a load uniformly distributed of the surface rim, modeling the impact of the blades, and mass forces distributed over the volume of the disk. It is assumed that the process of deformation of the rotor disk is linear. The stress intensity factor (CIF) are used to evaluate the fracture resistance. The steam turbine rotor disc is a massive axisymmetric body, which is why a semi-analytic finite element method is used to model the stress-strain state, which has been proven in a number of work for objects of this type. In the first stage, the distribution of stress-strain state of the rotor disc without crack is determined. The obtained results showed that maximum stresses occur in the region of the inner hole of the rotor disk. The following was to determine the fracture resistance of the rotor disc with a crack that may appear under the highest stress level. The configuration of the crack front is elliptical. The obtained results shows that the CIF attains the maximum value at the point furthest from the inner hole. The influence of ellipticity on the maximum values of CIF was investigated. The maximum CIN values for the rotor disc were determined using the approximate method used in the design of such objects. It involves the results of the known formula used to determine the CIF in the plate with a lateral crack. Comparison of results shows the nesecity of calculate such objects in the spatial formulation. There are significant limitations to the use of the two-dimensional approach to determine CIF in such objects.

Theoretical Investigation of Stresses Induced at Blade Mounting Locations in Steam Turbine Rotor System

One of the most common incipient losses of integrity in mechanical structures is the development and propagation of cracks. Especially in rotating members like steam turbine rotors etc. cracks, because of their potential, cause catastrophic failures and are a grave threat to an uninterrupted operation and performance. A crack may propagate from some small imperfections on the surface of the body or inside of the material and it is most likely to appear in correspondence to high stress concentration. Crack propagation path is generally determined by the direction of maximum stress or by the minimum material strength. Hence determination of stresses induced has been the focus of attention for many researchers. In the present work, development of a mathematical model to determine the stresses induced in a rotating disc of varying thickness is studied. This model is applied to a steam turbine rotor disc to determine the induced stresses and radial deflection. The mathematical modeling results are validated with the results obtained using Ansys package. The results of the present study will be useful in diagnosing the location and magnitude of maximum stress induced in the turbine rotor disc and stress intensity factor due to the presence of crack.

Effect of Ingress on Flow and Heat Transfer Upstream and Downstream of a Rotating Turbine Disc

Ingress is the penetration of a hot mainstream gas in a turbine annulus through the rim seal into the wheel-space between the rotating turbine disc (the rotor) and the adjacent stationary casing (the stator). Purge flow is used to prevent or reduce ingress, and the sealing effectiveness relates the flow rates of the purge and ingress. In this paper, an adiabatic effectiveness is used to relate the temperatures of a thermally-insulated rotor, the purge flow and the ingress. A non-dimensional buffer parameter, Ψ, is used to relate the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, respectively. This paper reports the first experimental study of the effect of ingress and purge flow on the adiabatic temperatures of both upstream and downstream surfaces of the rotor. Measurements of concentration and swirl over a range of purge have been obtained in wheel-spaces upstream and downstream of the rotor in a turbine rig. In transient heating tests, fast-response thermocouples were used to measure the temperature of the air in the wheel-space core; simultaneously, the temperatures of the upstream and downstream rotor surfaces were determined from infra-red sensors. The extrapolated steady-state temperatures (obtained using a maximum-likelihood estimation analysis) were used to determine the adiabatic effectiveness as a function of purge flow rate. The buffer effect of the purge flow for both wheel-spaces was quantified via comparisons between the variation of Ψ with purge flow rate. It was shown that the sealing effectiveness for the downstream wheel-space was larger than for the upstream. Consequently, and consistent with the theoretical model, the buffering effect of the purge flow was shown to be smaller downstream.