核电机组汽轮机低压叶轮叶根槽应力腐蚀裂纹扩展寿命分析

分析核电机组汽轮机低压叶轮应力腐蚀发生的机理及应力腐蚀裂纹扩展的原因,结合Clark模型和腐蚀环境下的Pairs模型建立应力腐蚀裂纹扩展寿命的计算模型。以某核电机组汽轮机的低压第2级、第3级叶轮叶根槽为研究对象,对应力腐蚀裂纹扩展寿命进行研究分析。结果表明:采用2种模型计算的裂纹扩展寿命均满足核电机组汽轮机耐用件使用寿命(60年)的要求。Pairs模型下的裂纹扩展寿命相比于Clark模型更加保守,在使用Clark模型对裂纹扩展寿命估算时,可以选取2~3的安全系数,并且温度变化对Clark模型下的裂纹扩展速率有较大的影响。

Detection of Blade Mistuning in a Low Pressure Turbine Rotor Resulting from Manufacturing Tolerances and Differences in Blade Mounting

For a serious prediction of vibration characteristics of any structure, a detailed knowledge of the modal characteristic is essential. This is especially important for bladed turbine rotors. Mistuning of the blading of a turbine rotor can appear due to manufacturing tolerances or because of the blading process itself due to unequal mounting of the blades into the disk. This paper investigates the mistuning of the individual blades of a low pressure turbine with respect to the effects mentioned above. Two different rotors with different aerodynamic design of the blades were investigated. The blades were mounted to the disk with a so-called hammer head root which is especially prone to mounting irregularities. For detailed investigations, the rotor was excited with a shaker system to detect the forced response behavior of the individual blades. The measurements were done with a laser vibrometer system. As the excitation of rotor structure was held constant during measurement, it was possible to detect the line of nodes and mode shapes as well. It could be shown that the assembly process has an influence on the mistuning. The data were analyzed and compared with numerical results. For this, different contact models and boundary conditions were used. The above described characterization of modal behavior of the rotor is the basis for the upcoming aeroelastic investigations and especially for the blade vibration measurements of the rotor, turning with design and off-design speeds.

Large eddy simulation of unsteady transitional flow on the low-pressure turbine blade

The aim of this paper is to predict the phenomenon of laminar separation, transition and reattachment in a low-pressure turbine （LPT）. Self-developed large eddy simulation program of compressible N-S equations was used to describe the flow structures of T 106A LPT blade profile at Reynolds number of 1.1×10^5 based on the exit isentropic velocity and chord length. The com- putational results show the distributions of time-averaged wall-static pressure coefficient and mean skin-friction coefficient on the blade surface. The locations of laminar separation and reattachment points occur around 87% and 98% axial chord, which agree well with experiment data. The two-dimensional shear layer is gradually unstable along the downstream half of the suc- tion side as a result of the spanwise fluctuation and the roll up of shear layer via Kelvin-Helmholtz （KH） instability. Three-dimensional motions appear near 84% axial chord which later triggers spanwise vortexes and streamwise vortexes, leading to transition to turbulence in the separation bubble. Through introducing the concept of dissipation function, the high loss mainly comes from the places where strong shear layer and intense fluctuation exist. Furthermore, the separation region is only an accumulation center of the low-energy fluid rather than an area of loss source.

Effects of Nozzle-Strut Integrated Design Concepton on the Subsonic Turbine Stage Flowfield

In order to shorten aero-engine axial length,substituting the traditional long chord thick strut design accompanied with the traditional low pressure(LP) stage nozzle,LP turbine is integrated with intermediate turbine duct(ITD).In the current paper,five vanes of the first stage LP turbine nozzle is replaced with loaded struts for supporting the engine shaft,and providing oil pipes circumferentially which fulfilled the areo-engine structure requirement.However,their bulky geometric size represents a more effective obstacle to flow from high pressure(HP) turbine rotor.These five struts give obvious influence for not only the LP turbine nozzle but also the flowfield within the ITD,and hence cause higher loss.Numerical investigation has been undertaken to observe the influence of the Nozzle-Strut integrated design concept on the flowfield within the ITD and the nearby nozzle blades.According to the computational results,three main conclusions are finally obtained.Firstly,a noticeable low speed area is formed near the strut's leading edge,which is no doubt caused by the potential flow effects.Secondly,more severe radial migration of boundary layer flow adjacent to the strut's pressure side have been found near the nozzle's trailing edge.Such boundary layer migration is obvious,especially close to the shroud domain.Meanwhile,radial pressure gradient aggravates this phenomenon.Thirdly,velocity distribution along the strut's pressure side on nozzle's suction surface differs,which means loading variation of the nozzle.And it will no doubt cause nonuniform flowfield faced by the downstream rotor blade.

Aerodynamic Loading Distribution Effects on the Overall Performance of Ultra-High-Lift LP Turbine Cascades

The present paper reports the results of an experimental investigation aimed at comparing aerodynamic perform- ance of three low-pressure turbine cascades for several Reynolds numbers under steady and unsteady inflows. This study is focused on finding design criteria useful to reduce both profile and secondary losses in the aero-engine LP turbine for the different flight conditions. The baseline blade cascade, characterized by a standard aerodynamic loading （Zw=1.03）, has been compared with two Ultra-High-Lift profiles with the same Zweifel number （Zw=1.3 for both cascades）, but different velocity peak positions, leading to front and mid-loaded blade cascade configurations. The aerodynamic flow fields downstream of the cascades have been experimentally in- vestigated for Reynolds numbers in the range 70000〈Re〈300000, where lower and upper limits are typical of cruise and take-off/landing conditions, respectively. The effects induced by the incoming wakes at the reduced frequency ./＋=0.62 on both profile and secondary flow losses for the three different cascade designs have been studied. Total pressure and velocity distributions have been measured by means of a miniaturized 5-hole probe in a tangential plane downstream of the cascade for both inflow conditions. The analysis of the results allows the evaluation of the aerodynamic performance of the blade cascades in terms of profile and secondary losses and the understanding of the effects of loading distribution and Zweifel number on secondary flows. When operating un- der unsteady inflow, contrarily to the steady case, the mid-loaded cascade has been found to be characterized by the lowest profile and secondary losses, making it the most attractive solution for the design of blades working in real conditions where unsteady inflow effects are present.

A Method for the Determination of Turbulence Intensity by Means of a Fast Response Pressure Probe and its Application in a LP Turbine

This paper describes the measurements and the post-processing procedure adopted for the determination of the turbulence intensity in a low pressure turbine (LPT) by means of a single sensor fast response aerodynamic pressure probe. The rig was designed in cooperation with MTU Aero Engines and considerable efforts were put into the adjustment of all relevant model parameters. Blade count ratio, airfoil aspect ratio, reduced massflow, reduced speed, inlet turbulence intensity and Reynolds numbers were chosen to reproduce the full scale LP turbine. Measurements were performed adopting a phase-locked acquisition technique in order to provide the time resolved flow field downstream of the turbine rotor. The total pressure random fluctuations are obtained by selectively filtering, in the frequency domain, the deterministic unsteadiness due to the rotor blades and coherent structures. The turbulence intensity is derived from the inverse Fourier transform and the correlations between total pressure and velocity fluctuations. The determination of the turbulence intensity allows the discussion of the interaction processes between the stator and rotor for engine-representative operating conditions of the turbine.

Computational Investigation of Blade Slotting on a High-Load Low-Pressure Turbine Profile at Various Reynolds Numbers:Part Ⅱ——Optimization of Slotting Position

The concept of using blade slotting to suppress the large boundary layer separation of high aerodynamic loading low pressure turbine profile has been developed in Part 1.Calculated results highlight the inability performance accompanied with un-proper blade slotting at high Reynolds number,blade slotting optimization seems like compulsory.Meanwhile,to further dignify the rational for use of blade slotting,slotting position and its geometry needed to be optimized.Comparison of different slotting scheme calculation results promised that blade slotting parameter like outlet angle and outlet position are the most important parameters which must be investigated to satisfy the design purpose.

Free-stream Turbulence Effects on the Boundary Layer of a High-lift Low-Pressure-Turbine Blade

The suction side boundary layer evolution of a high-lift low-pressure turbine cascade has been experimentally in- vestigated at low and high free-stream turbulence intensity conditions. Measurements have been carded out in order to analyze the boundary layer transition and separation processes at a low Reynolds nttmber, under both steady and unsteady inflows. Static pressure distributions along the blade surfaces as well as total pressure distri- butions in a downstream tangential plane have been measured to evaluate the overall aerodynamic efficiency of the blade for the different conditions. Particle. Image Velocimetry has been adopted to analyze the time-mean and time-varying velocity fields. The flow field has been surveyed in two orthogonal planes （a blade-to-blade plane and a wall-parallel one）. These measurements allow the identification of the Kelvin-Helmholtz large scale cohe- rent structures shed as a consequence of the boundary layer laminar separation under steady inflow, as well as the investigation of the three-dimensional effects induced by the intermittent passage of low and high speed streaks. A close inspection of the time-mean velocity profiles as well as of the boundary layer integral parameters helps to characterize the suction side boundary layer state, thus justifying the influence of free-stream turbulence intensity on the blade aerodynamic losses measured under steady and unsteady inflows.

Heat Transfer and Aerodynamics of Complex Shroud Leakage Flows in a Low-Pressure Turbine

A numerical investigation on over-shroud & inter-shroud leakage flow has been carried out to explore the underneath flow physics at the stage of shrouded Low Pressure(LP) turbine.Compared with the No inter-Shroud gap's Leakage flow Model(NSLM) and With inter-Shroud gap's Leakage flow Model(WSLM),the aerodynamic characteristics and the heat transfer performance have been studied.Through the aerodynamic point of view,it is concluded that due to the pressure difference between the rotor's passage and the over-shroud cavity,in the stream-wise direction,flow structure has been modified,and the inter-shroud leakage flow may even cause flow separation in the vicinity of the blade passage's throat.In the circumferential direction,separation flows appear over the rotor's shroud surface(upper platform of the shroud).Meanwhile,from the point of view of heat transfer,further provision on contour maps of the non-dimensional Nusselt number reveals that the reattachment of leakage flow would enhance the heat transfer rates and endanger the rotor's labyrinth fins over the shroud.However,due to the limited amount of inter-shroud leakage flow(current computational model),temperature distribution variation along the blade surface(near the rotor's tip section) seems to have only minor insignificant differences.At the end of the paper,the author puts forward some recommendations for the purpose of future successful turbine design.

Effects of Freestream Turbulence on Bypass Transition of Separated Boundary Layer on Low-Pressure Turbine Airfoils

This paper presents experimental studies on bypass transition of separated boundary layer on low-pressure turbine airfoils,focusing on the effects of freestream turbulence on the transition process.Hot-wire probe measurements are performed on the suction side of an airfoil in the low-pressure linear turbine cascade at several Reynolds number conditions.Freestream turbulence is enhanced by use of turbulence grid located upstream of the cascade.The results of this experimental study show that the location of boundary layer separation does not strongly de-pend on the freestream turbulence level.However,as the freestream turbulence level increases,the size of separa-tion bubble becomes small and the location of turbulent transition moves upstream.The size of separation bubble becomes small as the Reynolds number increases.At low freestream turbulence intensity,the velocity fluctuation due to Kelvin-Helmholtz instability is observed clearly in the shear layer of the separation bubble.At high frees-tream turbulence intensity,the streak structures appear upstream of the separation location,indicating bypass transition of attached boundary layer occurs at high Reynolds number.