Stator Blade Surface Research Articles

Numerical study on cooling performance and thermal stress characteristic of an f-class gas turbine stator blade

In this study, a coupled numerical computation approach integrating aerothermal and thermomechanical effects was employed to investigate the cooling efficiency and thermal stress characteristics of gas turbine stator blades. A comprehensive analysis was conducted considering varying turbulence intensities in the coolant flow (spanning from 0.05 to 0.15) and different coolant media configurations, including pure air, dual-medium mixture of air and steam, and pure steam. The distributional traits of cooling efficiency and thermal stress on the stator blade surface under these conditions were meticulously examined. Furthermore, quantitative assessments were performed to determine the extentto which coolant turbulence intensity and coolant type affect the average cooling efficiency and maximum equivalent thermal stress of turbine stator blades, thereby revealing the influence laws. The results reveal that the minimum cooling efficiency on the stator blade surface predominantly occurs at the position of channel 4 on the pressure surface, while the highest cooling efficiency is generally found near the leading edge of the suction surface. Regions of elevated thermal stress were consistently concentrated around the stator blade tip and root areas. When the coolant turbulence intensity increased from 0.05 to 0.15, the average cooling efficiency on the stator blade surface improved by 2.06%, accompanied by a reduction of 1.12% in the maximum thermal stress. In comparison to pure air cooling, dual-medium (air and steam) cooling and pure steam cooling lead to respective enhancements in the average cooling efficiency of approximately 3.3% and 13.2%, with corresponding decreases in the maximum thermal stress of 2.18% and 10.2%.

Numerical Investigation of Unsteady Rotor–Stator Interaction Mechanism and Wake Transportation Characteristics in a Compressor with Non-Uniform Tip Clearance Rotor

This study aims to numerically investigate a transonic compressor by solving the unsteady Reynolds-averaged Navier–Stokes equations. The flow mechanisms related to unsteady flow were carefully examined and compared between rotors with non-uniform tip clearance (D1) and small-value tip clearance (P1). The unsteady flow field near the 50% and 95% blade span characterized by unsteady rotor–stator interaction was analyzed in detail for near-stall (NS) conditions. According to the findings, the perturbation of unsteady aerodynamic force for the stator is much bigger than that of the rotor. At the mid-gap between the rotor and stator, the perturbation of tangential velocity of the D1 scheme in the rotor and stator frame is reduced. At the rotor’s outlet region, the perturbation intensity is divided into three main perturbation regions, which are respectively concentrated in the TLV near the upper endwall, the corner separation at the blade root, and the wake of the whole blade span. Through the analysis of the wake transportation characteristics, it was found that when the wake passes through the stator blade surface, the wake exerts a substantial influence on the flow within the stator passage. It further leads to notable pressure perturbations on the stator’s surface, as well as affecting the development and flow loss of the boundary layer. The negative jet effect induces opposite secondary flow velocity on both sides of the wake near the stator’s surfaces. Therefore, the velocity at a specific point on the stator’s suction surface will decrease and then increase. Conversely, the velocity at a particular point on the pressure surface will increase and then decrease.

Research on dehumidification optimization of steam turbine wet steam stage hollow stator cascade heating

The secondary water droplets in the steam turbine wet steam stage are easy to cause water erosion damage to the rotor cascade, and there is a large speed slip between the main steam flow and the secondary water droplets, which will seriously affect the safe and stable operation and reduce the efficiency of the steam turbine. Secondary water droplets are formed when the water film deposited on the stator blade surface falls off at the trailing edge. Therefore, controlling the formation of a water film on the stator blade surface plays an important role in improving the efficiency and safety of the steam turbine wet steam stage. Based on the current research situation at home and abroad, taking the Dykas cascade as the research object, it is found that the covering area of dry steam film on blade surface expands with the increase of temperature and flow of hot steam inlet. With the increase of hot steam back-pressure, the wetness of blade surface increases. When the average heat flux on the blade surface reaches 5000W/m2, there will be no water film falling off the blade surface. By orthogonal test, the expression between the average heat flux on the blade surface, the inlet temperature, the flow rate and the back-pressure was obtained. The research results can provide reference for the parameter design of steam turbine hollow stator heating dehumidification.

Experimental measurement of the flow-induced pulsation in a hydrodynamic turbomachinery stator and its pressure fluctuation characteristics

By means of experimental measurement of the transient internal flow field and the periodic lumped-blade separation analysis method (PLSAM), the pressure field distribution on a stator blade surface and the corresponding flow-induced pulsation, as well as the fluctuation characteristics in a torque converter are acquired and further analysed. The results show that there are fluctuation characteristics in both the blade pressure distribution results and the blade torque under the influence of flow induced pulsation, while the relationship between these fluctuations and the rotatory angle of the wheels reveals the mechanism of the flow induced pulsation; namely, the main cause of the flow induced pulsation lies in the successive switching of the turbine/pump blade position relative to the stator, which can be modelled by a trigonometric function in both the space domain and time domain, while the frequency domain characteristics of this trigonometric function exist in both the internal flow characteristics and performance results, which allows a connection to be built between the macro-performance and the micro-internal flow character and can be used for the inverse design of the cascade system.

Simulation of the effect of nonuniform fouling thickness on an axial compressor stage performance

This paper focuses on the numerical simulation of the flow status in the compressor with the condition of fouling. NASA stage 35 was considered as the object, and the commercial code ANSYS CFX was used. The deposition rate of contaminants on the surface was considered to be different along the height of the blade. A data from related study shows that the deposition rate of the contaminant on the side close to the hub is higher than the side near the shroud part. Based on the deposition law, this paper simulated the fouling of the compressor blades by changing the thickness on the blade surface. This subject only changed the thickness of the stator blade surface because of a data showing that the fouling on the stator blade surface is almost double that on the rotor blade surface. In the condition that the roughness value of the blade surface is constant, only the stable working range of the compressor is effected by the change of the surface thickness of the stator blade. There is a positive relationship between the value of compressor minimum flow rate and the value of thickness increment. After fouling the total pressure ratio and isentropic efficiency degenerated 1.59% and 3.76%, respectively.

The ultra-high efficiency gas turbine engine, UHEGT, Part II: A numerical study on reducing the stator blade surface temperature by indexing fuel injectors and using film cooling

In the Ultra-High Efficiency Gas Turbine Engine, UHEGT (introduced in our previous studies) the combustion process is no longer contained in isolation between the compressor and turbine, rather distributed within the axial gaps before each stator row. This technology substantially increases the thermal efficiency of the engine cycle to above 45%, increases power output, and reduces turbine inlet temperature. Since the combustion process is brought into the turbine stages in UHEGT, the stator blades are exposed to high-temperature gases and can be overheated. To address this issue and reduce the temperature on the stator blade surface, two different approaches are investigated in this paper. The first is indexing (clocking) of the fuel injectors (cylindrical tubes extended from hub to shroud), in which the positions of the injectors are adjusted relative to each other and the stator blades. The second is film cooling, in which cooling holes are placed on the blade surface to bring down the temperature via coolant injection. Four configurations are designed and studied via computational fluid dynamics (CFD) to evaluate the effectiveness of the two approaches. Stator blade surface temperature (as the main objective function) along with other performance parameters such as temperature non-uniformity at rotor inlet, total pressure loss over the injectors, and total power production by rotor are evaluated for all configurations. The results show that indexing presents the most promising approach in reducing the stator blade surface temperature while producing the least amount of total pressure loss.

The ultra-high efficiency gas turbine engine, UHEGT, part I: Design and numerical analysis of the multistage system

The Ultra-High Efficiency Gas Turbine Engine (UHEGT) was introduced in our previous studies. In UHEGT, the combustion process is no longer contained in isolation between the compressor and turbine. It is rather distributed in multiple stages and integrated within the high-pressure turbine stator rows. Compared to the current most advanced conventional gas turbines, UHEGT considerably improves the efficiency and output power of the engine while reducing its emissions and size. In this study, a six-stage UHEGT turbine with three stages of stator internal combustion is designed and analyzed. The design represents a single spool turboshaft system for power generation using gaseous fuels. The preliminary flow path for each turbine stage is designed by the meanline approach and modified using Computational Fluid Dynamics (CFD). Unsteady CFD calculation (via commercial software ANSYS CFX) is used to simulate and optimize the flow and combustion process through high-pressure turbine stages. The results show a base thermal efficiency of above 45% is achieved. It shows a successful integration of the multi-stage combustion process into the high-pressure turbine stages and a highly uniform temperature distribution at the inlet of each rotor row. High temperatures in some areas on the stator blade surfaces are controlled using indexing of fuel injectors and stator blades.

Influence of Pump Rotation Speed on Hydrodynamic Performance and Stator Blade Surface Pressure Pulsation in Torque Converter

Abstract An experimental investigation was performed to characterize the influence of pump rotation speed on the hydrodynamic performance and the associated unsteady pressure on the stator blade pressure-surface in a torque converter. High-resolution miniature transducers were used to obtain the signature of the pressure pulsation at specific surface locations. Results show that the increase of the pump rotation speed can enhance the torque capacity of the stator, leading to a higher torque ratio in the low speed ratio range and an improvement of the highest transmission efficiency. The efficiency increase rate starts to reduce at approximately SR = 0.4, corresponding to where the stator capacity reaches the maximum and exhibits a uniform distribution of the pressure pulsation intensity. The spectral decomposition of the pulsating pressure reveals the existence of two dominating frequencies, which corresponds to the upstream pump turbine interaction and the downstream pump blade passing. Higher pump speeds enhance the pump turbine interaction and results in a more regular pressure pulsation, improving the hydrodynamic performance of the torque converter.

Investigating the dehumidification characteristics of the low-pressure stage with blade surface heating

At present, the vast majority of electricity is generated by steam turbines. Nonequilibrium condensation will occur in the low-pressure stage, which will not only reduce efficiency but also corrode blades and endanger the safety of the steam turbine. The aim of this work is to optimize the blade surface volume heating scheme to reduce the wetness loss. Based on thermodynamic theory, the nucleation model and droplet growth model were studied. A two-fluid model of homogeneous condensation was established from the point of view of the volume average, and the accuracy of the model was verified. The effects of stator blade surface volume heating, rotor blade surface volume heating and coupling heating on the wet steam condensation characteristics in the nucleation stage were analyzed. The research shows that stator blade surface volume heating can satisfactorily prevent steam condensation. When the stator blade surface volume heating rate is 0.375 J /(mm2·s), the average outlet wetness of the stage is 0.0158, which decreases 69.34% compared with the non-heating condition, and the entropy increase is only 0.26% higher than that of the non-heating condition. Blade surface heating can inhibit steam condensation very well and improve the turbine efficiency to a certain extent.

Pressure Measurement and Analysis of Stator Blade Surface of Hydrodynamic Torque Converter

Pressure Measurement and Analysis of Stator Blade Surface of Hydrodynamic Torque Converter

Experimental study of the efficiency of steam injection on wet-steam turbine stator blade cascade

Currently, in order to decrease the negative effects caused by the presence of a discrete phase in the flow path of steam turbines stages operating in wet-steam area, different technical solutions are apply. These methods reduce the number of coarse droplets and wetness of working medium. The implementation of erosion reduction methods requires modifying surfaces of flow path, which can significantly affect the efficiency of the steam turbine. For example application of intrachanel moisture removing and steam injection needs changes of the stator blades surfaces. This article is a part of researches cycle about the efficiency of steam injection on the stator blade surface as the main method of coarse liquid particles diameters reduction in the last stages of high-power steam turbines. The paper presents the results of the analysis and comparison of experimental research unmodified profile to the profile of the stator blade changed by injection slot. The comparison of the profile losses considered blades is present. The analysis of the experimental results showed the feasibility and efficiency of this method of coarse liquid particles diameters reduction in the last stages of high-power steam turbines.

Numerical Investigation of the Droplet Behavior in Cascades Using a Finite Volume Method

This paper describes an Eulerian/Lagrangian two-phase model for wet steam. Two-dimensional inviscid transonic cascade flow is simulated using a cell-vertex finite volume space discretization method on structured triangular mesh. A pseudo time scheme is used to march the solution to steady state. The model provides an approach for including the interaction between the liquid and gas phases for a pure fluid. The analysis consists in the application of the discrete phase model, for modeling the liquid particle flow, and the Eulerian conservation equations to the continuous phase. The investigation permits us to know the influence of parameters such as: particle diameter, flow angle and particle velocity on deposition of drops onto stator blade surfaces. These parameters are analyzed to different inlet flow angles and drop sizes in the turbine. Deposition rate was found to be strongly dependent on increasing inlet flow angle and drop size in the example computed. The purpose of this paper is to present the results of some calculations of deposition which are based on more recent theories or less simplified flow models than previously published work

Effects of stator blade camber and surface viscosity on unsteady flow in axial turbine

The unsteady flow in turbine is extremely complicated and the wake further strengthens the unsteadiness. The vital effects of stator blade camber and surface viscosity on unsteady flow in axial turbine are revealed, aiming to improve aerodynamic performance. Single-stage models with straight stator, negative-bowed stator and positive-bowed stator are constructed. Then, viscous model and non-viscous model on stator blade surfaces are adopted respectively. The flow phenomenon including stator wakes and passage vortex are presented in the view of space and time. Moreover, time-averaged force and pulsating force changes are analyzed through time domain and frequency domain method. The results show that efficiency of turbine with non-viscosity stator surface is higher due to the weakening wakes and positive-bowed stator can reduce the end wall losses. Notably, the stator camber can reduce the aerodynamic exciting force through the wake structure change, and the aerodynamic exciting force for the investigated low gap turbine with stator surface viscosity is relatively lower since the wake induced by viscosity improves the potential flow field uniformity. The paper provides reference for efficiency improvement and aerodynamic exciting force reduction through wake control.

Investigation of the internal flow field for a subsonic stage of high pressure compressor through model testing

A large-scale four-stage low-speed research compressor was designed to represent the flow field structure in a subsonic stage, which is the seventh stage of a high pressure compressor. The aim of the design work was to undertake a careful high-to-low speed transformation. The low-speed compressor was designed as an “approximate repeating-stage” configuration, in which the third stage is the model stage and is slightly different from the other stages, while the first two stages and the last stage set up inlet and outlet conditions for it, respectively. The tip–hub ratio, solidity, and aspect ratio of the low-speed research compressor were restricted to be as close as possible to those of high pressure compressor. The blade sections along the span were designed to match the distributions of high-speed surface static pressure coefficient; furthermore, stacking rules of high pressure compressor apply to low-speed blades. The low-speed blades have been tested at the 4-Stage Research Compressor Facility of Nanjing University of Aeronautics and Astronautics. Detailed traverse flow measurements were conducted in the stator blade passages of the third stage and between blade rows, along with static pressure measurements on stator blade surface and particle image velocimetry measurements in the rotor passage. Experiment results show that due to the boundary layer separated below the mid-span of the rotor blade, the total pressure loss increases at the hub region of both the rotor and stator. In addition, the experimental results in the stator blade passage reflect the characteristics of the flow field in the bowed stator passage. The results indicated that the seventh stage of high pressure compressor needs to be optimized by inhibiting the boundary layer separation mainly on the rotor blade surface below the mid-span, which is our further work.

Unsteady numerical simulation of steam-solid two-phase flow in the governing stage of a steam turbine

Solid particle erosion (SPE) in an ultra-supercritical steam turbine control stage with block configuration is investigated numerically, based on the finite volume method and the fluid-particle coupling solver. We apply the particle discrete phase model to model the solid particles flow, and use the Euler conservation equations to solve the continuous phase. The investigation is focused on the influence of the solid particle parameters (such as particle diameter, particle velocity and particle trajectory) on the erosion rate of the stator and rotor blade surface in unsteady condition. The distributions of the highly eroded zone on the stator and rotor blade surfaces are shown and discussed in detail according to the mechanism of solid particle/blade wall interaction. We obtain that the erosion rate of the vane blade is sensitive to the fluctuation of the potential flow field, and the smaller particle has a greater impact on the erosion distribution of rotor blade. The erosion rate does not entirely depend on the diameter size of the solid particle.

Experimental Study on Effects of Slot Hot Blowing on Secondary Water Droplet Size and Water Film Thickness

The effects of the slot hot blowing of the hollow stator blades on the size of secondary water droplets and the thickness of the water film were experimentally investigated in this paper. The experiment was carried out on the turbine blade cascades in a wet air tunnel with an inlet air wetness fraction of 7.9%, an outlet air velocity of 170 m/s, a slot width of 1.0 mm, and a slot angle of 45 deg to blade surface. The Malvern droplet and particle size analyzer was utilized to measure the secondary water droplet size and distribution downstream of the hollow stator blades in the experimental tests. The experimental results show that the maximum diameter and Sauter mean diameter of the secondary water droplets were reduced greatly, and the water droplet size distribution became narrower. The larger blowing pressure difference resulted in the smaller secondary water droplets and the narrower water droplet size distributions. In addition, the efficiency of water separation from the hollow stator blade surfaces was higher for slot on the suction side than that of the pressure side case. Another simplified experimental test was also carried out on the flat plate to investigate the effect of slot hot blowing on the thickness of the water film downstream of the slot. The conductivity probes were used to measure the thickness of the water film downstream and upstream of the blowing slot. The results show that the slot hot blowing reduced the thickness of the water film downstream of the slot, which was affected by the blowing pressure difference and temperature difference between the hot blowing air and the main airflow. In conclusion, the slot hot blowing of the hollow stator blades has reduced the size of the secondary water droplets and secondarily has evaporated a little water film on the blade surfaces. Both effects are beneficial to reduce the erosion damage to the rotor blades.

Stator-Rotor Interactions in a Transonic Compressor—Part 2: Description of a Loss-Producing Mechanism

A previously unidentified loss producing mechanism resulting from the interaction of a transonic rotor blade row with an upstream stator blade row is described. This additional loss occurs only when the two blade rows are spaced closer together axially. Time-accurate simulations of the flow and high-response static pressure measurements acquired on the stator blade surface reveal important aspects of the fluid dynamics of the production of this additional loss. At close spacing the rotor bow shock is chopped by the stator trailing edge. The chopped bow shock becomes a pressure wave on the upper surface of the stator that is nearly normal to the flow and that propagates upstream. In the reference frame relative to this pressure wave, the flow is supersonic and thus a moving shock wave that produces an entropy rise and loss is experienced. The effect of this outcome of blade-row interaction is to lower the efficiency, pressure ratio, and mass flow rate observed as blade-row axial spacing is reduced from far to close. The magnitude of loss production is affected by the strength of the bow shock and how much it turns as it interacts with the trailing edge of the stator. At far spacing the rotor bow shock degenerates into a bow wave before it interacts with the stator trailing edge and no significant pressure wave forms on the stator upper surface. For this condition, no additional loss is produced.

Experimental Investigation of the Flow Field in an Automotive Torque Converter Stator

The flow field at the exit of a torque converter stator exit was measured using a miniature conventional five-hole probe. The data at speed ratio 0.8, 0.6, and 0.065 are presented. At the speed ratio 0.6, the stator exit flow is dominated by a large free-stream, accompanied by the blade wake and corner flow separation. A strong secondary flow is observed at the stator exit, the flow is overturned near the core and underturned near the shell. The secondary flow at inlet produces large radial transport of mass flow inside the stator passage. The shell-suction corner flow separation has a large blockage effect, resulting in losses. To determine the nature of the transitional flow in the stator passage, the surface hot-film sensors were mounted on the stator blade surface. The data confirm that the stator flow field is turbulent.

Numerical analysis and active control of wake/blade-row interaction noise

A computational approach for investigating and controlling the wake/blade-row interaction noise through the use of actuators or blowing/suction on the stator blade surfaces is presented in this paper. This approach includes a solution-adaptive finite volume upwind scheme, adaptive/dynamic mesh technique, boundary treatments for aeroacoustic computations, and an active noise control algorithm. A two-dimensional section of a fan stage, which is composed of an upstream rotor and a downstream fan exit guide vane (FEGV), is investigated. By utilizing a rotor wake model, the acoustic fields of the FEGV are presented and analyzed to understand the accuracy and suitability of the present adaptive scheme. Also, the noise generation mechanics are studied. Finally, the active noise control algorithm is introduced. From the computational results, the reduction of noise due to actuators on the blade surfaces is more significant than that of using blowing/suction. The downstream propagating acoustic waves are more difficult to control than the upstream propagating waves. [Work supported by NSC.]

A Loosely Coupled Unsteady Flow Simulation of a Single Stage Compressor

A steady/unsteady, three-dimensional Navier- Stokes solver that utilizes a semi-implicit, pressure-based solution procedure is developed to simulate the three-dimensional, incompressible flow through a single stage compressor. The present numerical scheme features the implementation of a second-order plus fourth-order artificial dissipation formulation to prevent the numerical oscillation due to central differencing schemes. A low-Reynolds-number form of the two-equation turbulence model is used to account for the turbulence effects. For unsteady flow computations, the coupling between the mean flow properties and the turbulence is enhanced by an inner-iteration procedure during each time step. The steady flow field in the rotor passage is computed first. This is used as input for the computation of the unsteady flow in the subsequent stator. The predicted unsteady pressure on the stator blades and unsteady velocities at several locations inside the passage are compared with the experimental data. The unsteady pressures on the stator blade surfaces are in good agreement with the experimental data. The predicted unsteady velocity components at various locations inside the stator blade rows are generally smaller than the measured values in the endwall regions. The phase, angle variations of the unsteady velocity are in good agreement with the measured values. The effects of the rotor wake, secondary and tip clearance flows on the unsteady flow through the subsequent stator are studied. An attempt is also made to quantify the contributions of incoming tip leakage flows and the endwall boundary layers on the unsteady flow through the downstream stator. It was found that the endwall boundary layers and tip leakage flows have a much stronger influence on the unsteady flow development than the wake.