Three-dimensional Blade Research Articles

Three-dimensional configuration tip rotor dynamics analysis

Abstract In order to analyze and study the dynamic characteristics of the 3D blade tip rotor, an aeroelastic dynamic model for a complex 3D blade tip rotor is established based on mechanics principles. The theory of medium deformation beam or large deformation beam is adopted as the blade structural dynamic model, and the quasi-steady and unsteady aerodynamic models (ONERA model) are adopted as the aerodynamic model. The rotor dynamics, aeroelastic stability and rotor loads of three-dimensional blade tip and rectangular blade tip are compared by examples. The analysis shows that both the forward and backward sweep angles have a certain effect on the rotor blade frequency, but the downward dihedral angle has little effect. The 3D tip configuration has the greatest influence on torsion mode frequency, followed by lagging mode frequency, which has little impact on flapping frequency. Reasonable design of forward and backward sweep angles and downward dihedral angles of 3D tip configuration can effectively reduce rotor loads, increase damping margin for aeroelastic stability, and improve stability.

Optimization design method based on parameter reduction and active subspaces: Redistribution of chordwise loading at blade tips in a transonic axial-flow fan

In practical optimization design, an excessive number of design variables have a highly detrimental influence on the efficiency and accuracy of the final design scheme and expose the optimization problem to the curse of dimensionality. Therefore, incorporating only the most essential variables into an optimization design problem facilitates obtaining accurate and cost-efficient solutions. Reported here is an optimization design method based on parameter reduction and active subspaces, and it is used to redistribute the tip load in a transonic fan. Specifically, a coupled design strategy is developed to reduce the number of parameters needed to describe the three-dimensional blade shape, which leads to far fewer design variables being involved in the optimization design. Moreover, active subspaces are used to perform sensitivity analysis and establish low-dimensional surrogate models. After the coupled design, a blade is represented effectively by only three parameters, each of which has a significant influence on the fan performance. Three one-dimensional active subspaces are established for maximum mass flow rate, maximum total pressure ratio, and maximum efficiency, based on which the linear surrogate models are obtained. Next, the chordwise tip blade loading is optimized, after which the rotor efficiency at the design point is increased by 1.1%, while the total pressure ratio remains nearly unchanged. Finally, the flow field is analyzed to understand the mechanism for this performance improvement, and the results show that the optimized blade loading reduces the aerodynamic losses caused by shock-induced flow separation and the interaction between shocks and tip leakage flows.

Enhancing Aerodynamic Performance of a Non-Axisymmetric Endwall Contoured Cascade Through Section Profiling Method

Abstract Endwall contouring and 3D blade configurations are effective techniques for enhancing turbomachinery performance. The integration of these technologies is an important area of investigation. To continue the numerical and experimental validations of the non-axisymmetric endwall contoured cascade (Du et al., 2024, “Endwall Contouring for Improving Aerodynamic Performance in a High-Pressure Turbine Cascade,” ASME J. Turbomach., 146(10), p. 101001), the present study redesigns the cascade via section profiling using optimization methods to maximize performance gains. To improve the control effect of endwall contouring, blade section parameters are strategically adjusted during optimization. The experimental flow field traverses at cascade exits demonstrate the control of the cascade flow field by the optimized design. The redesigned cascade exhibits decreased overturning near the shroud and reduced underturning near the hub, as well as reduced profile loss in the mainstream, compared to the endwall contoured cascade. The modification of section parameters enhances the control of losses and the secondary flow intensity. Computational fluid dynamics is used to provide a detailed analysis of the flow field, providing insights into how flow structures vary when the blade profile is modified. The numerical results further elucidate the effect of blade section profiling on both the performance characteristics of the cascade and the configuration of the secondary flows.

Experimental and numerical investigation on turbine flow control through integrating endwall contouring with section profiling at different Mach numbers

The efficiency of turbomachinery is notably impacted by losses occurring within the turbine cascade, which are intricately linked to the configuration and intensity of secondary flows. Non-axisymmetric endwall contouring, as well as three-dimensional blade designs, are effective methodologies for regulating secondary flows within the cascade passage. These passive control strategies are garnering increased attention due to their adaptability under off-design conditions. However, previous investigations have primarily scrutinized the flow intricacies in linear cascades. This study provides an in-depth examination of the adaptation of endwall contouring, both independently and in conjunction with section profiling, within annular cascades and a specific emphasis on Mach numbers and their influence on secondary flow control. Employing a blend of experimental and numerical techniques, the research elucidates how radial pressure gradients impact pressure distributions near the throat, leading to notable discrepancies in secondary structures between the lower and upper passages. Furthermore, the study highlights how endwall contouring significantly inhibits the progression of secondary vortices. The integration of endwall contouring with section profiling demonstrates enhanced performance by modulating flow angles compared to endwall contouring in isolation. Notably, the effects of these methodologies on pressure variations and secondary flow control exhibit an escalating trend with increasing Mach numbers, attributed to flow compressibility effects. Additionally, the study observes a consistent trend in the ability to mitigate losses as Mach numbers vary.

Experimental study on three-dimensional blade designs in an aggressive compressor transition duct

The increasing performance requirements for aero-engines necessitate the integrated design of compressor transition ducts with upstream components to reduce the axial length of the engine. This paper presents an experimental investigation of three-dimensional (3D) blade designs within an aggressive compressor transition duct integrated with the upstream stator. The aim is to reduce the total pressure loss and decrease the radial distortion of the flow field at the outlet of the transition duct, thus providing better inflow conditions for the high-pressure compressor. Detailed measurements of the internal flow field were conducted under both near stall (NS) and design (DE) conditions for three 3D blades. The results showed that in the downward path, adopting the 3D blades with positive dihedral and forward sweep contributed to mitigating the stator hub corner stall under the NS condition. Under the same operating conditions, enhanced kinetic energy at the stator root improved the spanwise uniformity of the transition duct outlet profile, while also increasing the anti-separation capability of the downstream hub boundary layer. The corner vortex at the stator root could enhance momentum mixing between the downstream hub boundary layer and the mainstream, thereby providing stronger separation resistance for the hub boundary layer under the NS condition. Compared to the baseline stators, the optimized 3D stators reduced system total pressure loss by 24% under the NS condition, while maintaining essentially unchanged total pressure loss under the DE condition.

An Aerodynamic Investigation of the Last-Stage Turbine in an Upgraded Gas Turbine

Abstract Due to the lengthy certification process for newly designed turbine blades, product upgrading of industrial gas turbine units is often performed solely on compressor and combustor. Since their inlet conditions are significantly changed, the entire four-stage turbine operates far away from its original design point, leading to decreased efficiency, and increased flutter risk. This investigation first performs numerical simulations to study the flow field change of the last-stage turbine in a gas turbine before and after product upgrading. To reduce the load of the last-stage turbine without reducing the power output of the whole turbine, the enthalpy drops of turbine are reallocated to the front three stages. After modifying the blade profile based on S1 stream surface analysis, a CFD simulation is carried out on the modified three-dimensional blade passage. It is shown that the modified blade design greatly reduces the Mach number at the tip outlet of the last-stage blade, thus possibly reducing flutter risk and improving the aerodynamic efficiency of the turbine. This paper also attempts to redesign the blade geometry by different radial blade stacking of both forward sweep and backward sweep. It is found that the backward-swept blade modification can effectively reduce the endwall flow loss. This work presents the improvements of the aerodynamic efficiency of last-stage through a series of improvement methods and provides a reference for future detailed optimization of this last-stage turbine.

3D multiscale dynamic analysis of offshore wind turbine blade under fully coupled loads

Wind turbine blades are typically sophisticated structures with complex geometry and composite layup. The realistic loads acting on blades serviced in harsh offshore environments are fully coupled dynamic loads involving wind, wave, current, servo-control, gravity and other inertial loads. This work presents an easy-to-implement methodology for the time-domain detailed analysis of three-dimensional (3D) blade structure, by combining fully coupled dynamic simulator and general finite element program. As a practical example subjected to multiple marine environmental loadings, one of the rotating composite blades atop a 5-Megawatt (MW) monopile-supported offshore wind turbine (OWT) in soft clay is used for verifying this method step by step, and the effect of rotation and foundation flexibility on blade behaviours is explored. Good agreement between OpenFAST and proposed method in tip deflections and root reaction loads is visible from validation results, and the recommendations on how to further improve this method in future iterations are made. Subsequently, based on stress-time history of blade composite layups, time-domain 3D multiscale analysis including the failure evaluation for layers in outer shell and shear webs using Tsai-Wu strength criteria, as well as the fatigue damage assessment of carbon spar caps was performed.

Optimization of Three-Dimensional Blade and Variable Stators for Efficiency and Stability Enhancement of Multistage Axial Flow Compressor at Variable Speeds

Abstract High efficiency and wide stability at variable speeds are equally important to the design and operation of multistage axial flow compressors. However, published research works on three-dimensional design optimization of compressors are so far mainly limited to a single blade row or stage at design speed due to the curse of dimensionality. Moreover, optimization of variable inlet guide vanes (IGV)/stators for off-design operations is carried out by using a rapid but low-fidelity prediction tool and is generally independent of design optimization of blade geometry. To tackle these issues, a three-dimensional holistic design and adjustment optimization method is developed in which both three-dimensional blade geometry and variable IGV/stators are optimized simultaneously for better efficiency and stability at design and off-design conditions. Metamodel-interpreted data mining method and adaptive infilling strategy are used respectively to enhance the capability of the metamodeling and optimization. The developed method is then applied to a modern highly loaded 3.5-stage transonic axial flow compressor at both design and part-design speeds. The results show that the stall margin is extended from 8.23% to 19.65% at 70% design speed while peak efficiency is slightly improved at design speed. The flow mechanisms responsible for the efficiency enhancement at design speed are mainly associated with the reduced total pressure loss in stators as well as inter- and intra-stage loading redistribution. The stability enhancement at 70% design speed is mainly achieved by loading the front blade rows while unloading the limiting rear blade row through variable IGV/stators adjustment. The developed holistic design and adjustment optimization method with the aid of metamodel-interpreted data mining is of great application value for the design and adjustment of advanced multistage axial flow compressors.

Understanding the Effect of Three-Dimensional Design in Tandem Blade

Abstract In order to maximize the pressure ratio and efficiency, compressor designers have tried several unconventional design approaches. Tandem blading is one such unconventional design that promises a higher pressure ratio per stage through a higher diffusion factor. The nozzle shape created between the forward and aft blades of a tandem configuration acts as a passive boundary layer control mechanism. The boundary layer growth over the aft rotor is therefore effectively controlled with the help of this gap-nozzle flow. The flow complexity is likely to increase in the case of a tandem rotor due to the twin leakage vortices, twin wake regions, and their interaction with the hub and casing boundary layers. Modern compressor blades are often designed with three-dimensional blade techniques such as sweep, lean, dihedral, end bent, etc., to reduce the various losses and achieve optimum performance. However, to the best of the author’s knowledge, the effect of 3D blade designs on the performance of tandem rotors has not been fully explored so far. A comprehensive numerical investigation is undertaken to understand the effect of 3D designs on the performance of tandem blades. Axial sweep and dihedral failed to improve the performance of the tandem rotor. Significant improvement in the stall margin is observed for the forward chordwise-swept and negative lean tandem rotors and is largely attributed to lower tip incidence. The performance penalty of the forward-swept and negatively leaned cases can be reduced by integrating compound or variable lean and sweep into the design.

Study on the combined influence of aerodynamic sweep and casing treatment in a transonic compressor rotor

Casing treatment and three-dimensional blade design are effective techniques to remedy the deficiency of compressor stability margin, yet their combined effects on compressor performance are seldom studied. With the help of URANS simulations, this paper explored the combined influence of aerodynamic sweep and casing treatment in a transonic compressor rotor. Compared with the configurations of single sweep and single casing treatment, the combined configuration presented an outstanding advantage for improving compressor performance. For compressor overall performance, the stall margin improvement of combined configuration was up to 11.8%, larger than single forward sweep and single casing treatment. Meanwhile, peak efficiency penalty of combined configuration (−1.02%) was significantly lower than that of single casing treatment. Under the effect of casing treatment, the results showed that the pulsating axial velocity could effectively delay the interface of the tip leakage flow and main flow, preventing the overflow of tip leakage flow. The distributions of blockage coefficient and loading coefficient indicated that combined configuration was more effective due to tip unload by casing treatment and blockage resistance ability by forward sweep. Furthermore, the spatial and temporal evolutions of axial velocity at slot opening surface were discussed in detail. Compared with the single casing treatment, higher positive axial velocity excitation and smaller range of negative axial velocity were introduced by combined configuration, which contributed to better stability enhancement.

CFD analysis of hydrodynamic force on a horizontal axis tidal turbine

Horizontal axis tidal turbines are similar to wind turbines in both geometry and principle of operation, yet they need to withstand much heavier loadings and extreme conditions in a harsh operating environment. Consequently, the loadings on tidal turbine blades need to be accurately evaluated within the design stage to ensure they can withstand loadings with little need for repair. With the advancement of computational capabilities, computational fluid dynamics offers a relatively inexpensive method of simulating working conditions and estimating loadings, compared to traditional physical testing, while maintaining accuracy and applicability under a range of operating conditions. In this research, a computational fluid dynamics model of a tidal turbine rotor has been developed using commercial code ANSYS CFX, where the three-dimensional blade geometry is developed from the prototype tidal turbine used in the Round Robin Tests in the framework of the H2020 MaRINET2 Infrastructures Network project. The outputs from the numerical model are validated against the experimental results, where it is revealed that with an increasing rotating speed of the tidal turbine, the thrust force that turbine experienced increases, while the torque force experiences a rise firstly, reaching a maximum value and then decreases gradually. In addition, the experimental results show that during the operation of ocean tidal turbines, the turbine blades experience frequent and large-scale fluctuation of hydrodynamic loads, including thrust and torque, which may lead to tidal turbine blade damage due to fatigue. Therefore, the next stage of development with this numerical model is fatigue loading evaluation, in order to improve the present fatigue design and testing of tidal turbine blades, while gaining a greater understanding of the damage mechanisms.

Three-Dimensional Flow Simulation by a Hybrid Two-Phase Solver for the Assessment of Liquid/Gas Transport in a Volute-Type Centrifugal Pump with Twisted Blades

A hybrid two-phase flow solver is proposed, based on an Euler–Euler two-fluid model with continuous blending of a Volume-of-Fluid method when phase interfaces of coherent gas pockets are to be resolved. In a preceding study on a two-dimensional bladed research pump with reduced rotational speed, the transition from bubbly flow to coherent steady gas pockets observed in optical experiments with liquid/gas flow could be well captured by the hybrid solver. In the present study, the experiments and solver validation are extended to an industrial-scale centrifugal pump with twisted three-dimensional blades and elevated design rotational speed. The solver is combined with a population balance model, and a scale-adaptive turbulence model is employed. Compared to the two-dimensional bladed pump, the transition from agglomerated bubbles flow to attached gas pockets is shifted to larger gas loading, which is well captured by the simulation. The pump head drop with increasing gas load is also reproduced, showing the hybrid solver’s validity for realistic pump operation conditions.

Aerodynamic load evaluation of leading edge and trailing edge windward states of large-scale wind turbine blade under parked condition

The safety and reliability of wind turbine blades are increasingly challenged by extreme wind conditions such as typhoons, as wind turbines tend to become larger. Under these conditions, most units will be shut down and the blades will be pitched to around 90° to minimize the loads. This paper aims to compare a new strategy for the parked condition, i.e., the trailing edge windward state, with the traditional leading edge windward state to verify its technical feasibility. The aerodynamic loads of a 30%-thickness airfoil and a commercial wind turbine blade are comprehensively evaluated by wind tunnel experiment, CFD simulation and engineering analytical model. The two-dimensional airfoil cases indicate that the airfoil resultant force is lower in the trailing edge windward state than in the leading edge windward state for a wide range of angles of attack. Consequently, the three-dimensional blade cases shows that the low load region of the trailing edge windward state is relatively wider than that of the leading edge windward state. The averaged blade root load is reduced by 41.4% ~ 57.8% through trailing edge windward state with prescribed error bounds of windward angular. Besides, it is suggested that the traditional engineering analytical model should improve the precision of the extrapolated airfoil data around AOA = 180 deg. to ensure the accurate load evaluation under the trailing edge windward state. This study suggests a new control strategy for wind turbine blades under the parked condition, which offers significant benefits for load reduction and has a good potential for future applications.

A cost-effective CNN-BEM coupling framework for design optimization of horizontal axis tidal turbine blades

The paper proposes a novel cost-effective framework that combines deep learning convolutional neural network (CNN) and blade element momentum (BEM) models for optimizing the performance of three-dimensional (3D) horizontal axis tidal turbines (HATTs). The framework employs signed distance function (SDF) to reconstruct the three-dimensional blade geometry, utilizes CNN to identify the hydrodynamic performance of each blade section, and ultimately predicts the performance of HATT using BEM. On top of the new CNN-BEM model, the rotor blade geometrical optimization by multi-objective non-dominated sorting genetic algorithm (NSGA-II) is carried out to obtain a better trade-off solution with the maximal power coefficient of turbine and minimal hydrodynamic load exerted on the blades. The results show that the CNN-BEM model has good agreement with experimental data and reduces prediction time by 46.7% compared to the conventional Xfoil-BEM model, while reducing general optimization time by 20.1%. The new model's cost-efficiency allows for a better trade-off solution with reduced hydrodynamic load while maintaining the power coefficient. Thus, the proposed model has the capability to deliver both accurate and fast prediction and optimization of HATT performance, making it a valuable tool for guiding the design of tidal turbines.

Effects of Slotted Blades on the Hydrodynamic Performance of Horizontal Axis Tidal Turbines

The horizontal axis tidal turbine (HATT) is a device that harnesses the energy of ocean currents and converts it into electrical energy. The blade plays a crucial role in the efficiency of power generation in HATTs. This study focuses on the use of slotted blades to enhance the efficiency of HATTs and investigates the flow control mechanism of these slots using computational fluid dynamics (CFD) methods. Initially, CFD simulations were conducted to analyze the impact of the slot’s geometry parameters on a two-dimensional (2-D) slot and to demonstrate its passive fluid control mechanism. Subsequently, the slot was implemented on three-dimensional (3-D) blades to examine its effect on the hydrodynamic performance of the blades. The results of the 2-D simulation indicate that the width and position of the slots have a significant influence on the lift-to-drag ratio of the hydrofoils, resulting in a maximum increase of 166%. For the 3-D blades, the simulation results reveal that the slot can enhance the power coefficient of the blades, particularly at low tip-speed ratios, with a maximum increase of 7.8%.

Intelligent fault diagnosis of turbine blade cracks via multiscale sparse filtering and multi-kernel support vector machine for information fusion

For accurately identifying the crack severity of turbine blades, a novel intelligent diagnosis framework is proposed in our paper, which uses multiscale sparse filtering (MSF)-based unsupervised sparse feature learning and multi-kernel support vector machine for information fusion (MKSVMIF). To realize the technical readiness and the state-of-the-art diagnostic performance, advanced signal processing methods are used to eliminate interference and retain fault-related characteristics. Thus, the EEMD-based multiwavelet packet energy entropy (EEMD-WPEE) as an enhanced method is proposed for multi-source three-dimensional blade tip clearance signals (3D-BTC), which is used to enhance the fault-related information. Afterward, the MSF is constructed to adaptively learn multisource sparse features from EEMD-WPEE representation of 3D-BTC by an unsupervised manner. Finally, the MKSVMIF is proposed to fuse these sparse features and diagnose crack severities. To validate the effectiveness of our proposed MSF-MKSVMIF framework, Extensive experiments are conducted on a blade-rotor simulation rig, and the results show that our proposed framework is superior to other comparison methods and can quantitatively detect different blade crack severities with a relatively small number of samples.

Aerodynamic and structural multidisciplinary optimization design method of fan rotors based on blade curvature constraints

The optimization design of the actual fan/compressor rotors is a multidisciplinary problem. The aerodynamics and strength multidisciplinary optimization design of the fan/compressor rotors can improve the aerodynamic performance of rotors as much as possible under the condition of satisfying the structural strength requirements. However, the conventional multidisciplinary optimization of aerodynamics and structures will significantly increase the amount of computation cost and time period. Thus, it is difficult for conventional multidisciplinary optimization methods to be used in real-world engineering practices. In order to reduce the computational burden and time cost of the multidisciplinary optimization design, this paper firstly proposes a multidisciplinary optimization design method for rotors based on blade curvature constraints. In the optimization, the self-organizing map (SOM) method is applied to analyze and extract the constraint value of the blade curvature. And the blade curvature constraint value is used as a penalty function instead of the time-consuming high-fidelity FEM, which greatly reduces the computational cost and runtime of the multidisciplinary optimization. Besides, the Free-form deformation (FFD) method is adopted to realize the flexible deformation of the three-dimensional blade with the smallest number of design variables and polynomial chaos Kriging is used as a surrogate model for aerodynamic performance prediction in the optimization process. The method verification and mechanism analysis are carried out by studying a fan rotor. Data mining of FEM samples shows that, in the optimization design space, the maximum spanwise curvature of the blade is monotonically related to the maximum stress of the blade. And the maximum streamwise curvature, maximum spanwise slope, maximum streamwise slope, and maximum thickness of the blade have no related relationship with the maximum stress of the blade. Compared with the conventional multidisciplinary optimization design method based on the surrogate models of high-fidelity computational fluid dynamics (CFD) and finite element method (FEM), the time cost of the multidisciplinary optimization design method based on curvature constraints is reduced by 10 times, and the time cost of the multidisciplinary optimization is significantly reduced. The results show that, in terms of structural performance, the maximum stress of the aerodynamic optimization method without blade curvature constraints is 426 MPa, which exceeds the yield limit of aluminum alloy material (420 MPa), and the maximum stress of the multidisciplinary optimization design with blade curvature constraints proposed in this paper is 344 MPa. In terms of aerodynamic performance, the isentropic efficiency of the aerodynamic optimization method without blade curvature constraints and the method proposed in this paper are increased by 2.1% and 1.8%, respectively. Therefore, the proposed method reduces the maximum stress of the blade by 19.5% with little influence on the aerodynamic performance.

Aerodynamic optimization and analysis of quadrotor blades operating in the Martian atmosphere

The design of unmanned aerial systems (UAS) for flight in the Martian atmosphere is a relevant and current topic. The successful flight of the Ingenuity helicopter recently proved its applicability. We present a numerical approach to the aerodynamic optimization of blades for rotors working in flow regimes with Reynolds numbers smaller than 15,000. Due to the atmospheric gas density and viscosity on Mars and the required rotation speed and rotor diameter, rotary-wing works mainly in the so-called ultra-low Reynolds number regime (103<Re<104), where the flow is likely laminar. The tip region is in the lower range of the very-low Reynolds number regime (104<Re<105), where separation-induced laminar-turbulent transition may occur. Such conditions characterize rotor blades of UAS operating in the Martian atmosphere or at very high altitudes (30 km) in the Earth's atmosphere. The blade design procedure consists of a two-step optimization process. The process starts with an initial two-dimensional airfoil design analysis followed by three-dimensional Blade Element Momentum (BEM) simulations to achieve the chord and twist radial distributions necessary to define the blade geometry. Then, a procedure to perform three-dimensional adjoint-based CFD simulations enhances the performance. The aerodynamic characteristics of optimal blades are evaluated with Navier-Stokes (N-S) and Large Eddy Simulations (LES), demonstrating the negligible effect of turbulence in blade performance for these Reynolds numbers when the boundary layer is attached. The implemented BEM method and high-fidelity CFD simulations show a good agreement.

Dynamic modeling of rotary blade crack with regard to three-dimensional tip clearance

To investigate the dynamic characteristics of the three-dimensional blade tip clearance (3D-BTC) of rotary blade cracks, a novel dynamic model of the rotary blade crack with regard to the 3D-BTC is derived based on the Timoshenko beam theory. In this model, the modal shape functions of the blade are derived based on the transfer matrix method, and the axial and circumferential aerodynamic loads are introduced to better obtain the dynamic responses of the blade vibration. Then, a breathing crack model of the blade trailing edge crack is established by considering the coupling effects of the centrifugal stress, axial bending stress, and circumferential bending stress. The crack opening width is introduced into the breathing crack model to comprehensively depict the crack together with the crack depth and crack location. Moreover, a numerical calculation method for the 3D-BTC is proposed for the rotary blade with cracks. The dynamic model is validated by comparing it with the finite element model and the experiment. Finally, the effects of the blade trailing edge crack on the 3D-BTC are analyzed. The results show that the cracked blade's first-order natural frequency decreases with the crack depth increase, and it increases first and then decreases slightly when the crack location moves away from the blade root. The effects of crack opening width on the first-order natural frequency are relatively small due to its small size. In the meantime, the nonlinear damage indicators (NDIs) of the 3D-BTC are calculated. The results show that the NDIs can reflect the severity of the blade crack, and the proposed model can comprehensively analyze the effects of rotary blade crack on the 3D-BTC, which is beneficial for the diagnosis method for blade cracks based on the 3D-BTC.

Dynamic Characteristics Analysis of 3D Blade Tip Clearance for Turbine Blades with Typical Cracks

As well known, the crack is a typical fault of turbine blades, which is difficult to detect due to the weak fault features contained in the rotor vibration. Although some fault diagnosis methods based on blade tip timing (BTT) are proposed to detect blade cracks, the limited fault features can be extracted because the BTT signals contain only one-dimensional fault information. Based on the dynamic analysis, the cracked blade undergoes three-dimensional (3D) deformation so that it would be reflected in the changes of the three-dimensional blade tip clearance (3D-BTC). Therefore, the dynamic characteristics of the 3D-BTC of turbine blades with typical cracks should be investigated to obtain its change rule and achieve a more comprehensive diagnosis of blade cracks. In this paper, the 3D finite element model of the turbine blisk is established, and the fluid-thermal-solid coupling analysis is implemented to calculate the blade deformation. Then, a novel dynamic computation method is proposed to calculate the 3D-BTC based on the blade deformation. The typical blade cracks are taken into consideration, and the dynamic characteristics of the 3D-BTC regarding the typical cracks are analyzed to obtain its change rule. The results show that abundant crack fault information can be obtained based on the 3D-BTC, which can facilitate the comprehensive diagnosis of turbine blade cracks.