Flow In Turbine Stage Research Articles

The effects of stator-rotor interaction on unsteady characteristics of turbine tip leakage flow

The unsteady flow characteristics of tip leakage flow significantly affect the operation stability of the turbine blade. However, there is currently a lack of research on the unsteady flow characteristics of the tip leakage flow under the stator-rotor interaction. Through experiments with a rotating turbine and simulations of the entire stage and full-annulus turbine stage flow using a self-adaptive method, this study investigates both experimentally and theoretically the impacts of rotor-stator interaction on the dynamic behavior of the tip leakage flow in the turbine. The impacts of stator-rotor interaction on pressure oscillations, mixing, and vortex evolution within the tip leakage flow are investigated. Furthermore, the mechanisms underlying the influence of stator-rotor interaction on the dynamic behavior of the tip leakage flow at different rotor speeds and different tip gaps are also analyzed. The results indicate that the passage vortex (PV) of the guide vane aggravates the instability phases experienced by the tip leakage vortex (TLV), namely vortex wandering and breakdown. Besides, the pulsation intensity of the tip leakage flow decreases, while the pulsation frequency increases as the rotational speed increases. Additionally, it is also observed that there is a significant increase in high-frequency and large-amplitude oscillations in the tip leakage flow with increasing tip gap heights.

Numerical investigation of unsteady film cooling on turbine blade squealer tip with pressure side coolant

Unsteady film cooling characteristic from pressure side coolant in squealer tip in turbine stage was investigated by numerical simulation. Due to unsteady flow in turbine stage, flow characteristics and blowing ratio of coolant from various holes fluctuate and change cooling effectiveness on squealer rim, cavity floor and side wall. In unsteady simulation, deterioration of coolant coverage causes unsatisfied cooling performance on squealer tip, which results in the maximum reduction of 18.3% and 20% of cooling effectiveness on squealer rim and cavity floor at specific instants compared to steady simulation. In different moments, pressure side coolant increases average heat transfer coefficient on pressure side squealer rim by 15% ∼ 47% and forms discrete distribution of high heat transfer coefficient there. Unsteady heat transfer on squealer rim is much intense compared to steady condition. Raising blowing ratio and decreasing cavity depth promote cooling effectiveness in tip cavity. Too small blowing ratio might lead to the risk of high temperature mainstream invasion into some pressure side film holes. Cooling effectiveness in tip cavity increases with cavity depth decreasing. Due to relative motion between blade tip and shroud, scraping vortex pushed rolling vortex more closely to pressure side and thus facilitates coolant to touch cavity floor.

Unsteady simulation of flow and heat transfer in a transonic turbine stage under non-uniform inlet conditions

In modern aero-engines, the temperature non-uniformity (hot-streak) caused by the combustors and secondary flows caused by the rotor blades have a considerable impact on the aerothermal performances of the high pressure (HP) turbine. In this study, two idealized hot-streaks (radial and rounded) from literature and one engine representative hot-streak (distorted) were evaluated within a HP turbine stage using unsteady numerical simulation. The results were analyzed and discussed and they include, the stage performance, unsteady flow visualization, unsteady hot-streak transport, secondary flows/hot-streak interaction and blades thermal loading. It was found that the rotor passage had various complex secondary flows and the boundary layer on its surface undergone several transitions. The hot-streak transport and its contact with vane and rotor blades differed from one case to another. The secondary flows had a remarkable impact on the rotor exit temperature. They induced wavy shapes and corrugations of temperature gradients near the endwalls. All hot-streaks were completely deformed and distorted across the turbine stage. The rotor surfaces suffered from hot temperatures under radial and distorted hot-streaks compared with rounded hot-streak. Very high levels of the heat transfer were generated on the rotor suction side near the endwalls due to the vortices.

Energy dissipation analysis based on velocity gradient tensor decomposition

A velocity gradient tensor decomposition method based on a normal frame is introduced in this paper. The velocity gradient tensor is decomposed into a compression–stretching tensor, pure rotation tensor, and pure shear tensor. The analysis shows that both the strain rate tensor and vorticity tensor in Helmholtz velocity decomposition contain shear tensor components, and the total pure shear tensor is the combination of shear components in the two tensors. Based on this decomposition and the physical meaning of each tensor term, the energy dissipation of the channel flow with or without a pressure gradient and a turbine passage flow are analyzed. The results show that the energy dissipation is caused by shear deformation and expansion and contraction deformation of the motion fluid, and pure rotation does not cause energy dissipation. In particular, the pure shear is the primary factor of energy dissipation. Shear accounts for 99.9% of energy dissipation in the fully developed turbulence of zero-pressure gradient channel flow, 99% of the energy dissipation in the separated boundary layer flow is caused by the pure shear, and 81% of the energy dissipation in the turbine stage flow is caused by pure shear.

Influence of fillet shapes on secondary flow field in a transonic axial flow turbine stage

Numerical experiments were conducted to investigate the effect of leading edge modifications via fillet shapes near vane/blade-endwall juncture in a transonic environment within the highly loaded high pressure turbine stage. The investigated fillet shapes were designed based on geometric parameters: leading edge radius and included angle. The geometrical modifications were achieved to achieve variation in fillet radii at vane/blade endwall juncture along the stream-wise direction, namely variable fillet and constant fillet. Further their influences were studied in both nozzle guide vane and rotor passage secondary flow field. Computational Fluid Dynamics (CFD) method was used to resolve the flow features inside the turbine passage for planar and fillet cases. The presented data highlight the secondary flow features and their behavior using topological properties of flow field aided with the streamline and iso-contour plots. The flow-field results show a significant reduction in the total pressure losses associated with the horse shoe vortex near the leading edge region as the fillet radii are varied. Overall in both vane and rotor passages, variable fillet outperforms the constant fillet by reducing the penetration length of three-dimensional regimes along its span, mitigating the boundary layer growth and improving the loss coefficients.

The efficiency of a pulsed detonation combustor–axial turbine integration

The paper presents a detailed numerical investigation of a pulsed detonation combustor (PDC) coupled with a transonic axial turbine stage. The time-resolved numerical analysis includes detailed chemistry to replicate detonation combustion in a stoichiometric hydrogen–air mixture, and it is fully coupled with the turbine stage flow simulation. The PDC–turbine performance and flow variations are analyzed for different power input conditions, by varying the system purge fraction. Such analysis allows for the establishment of cycle averaged performance data and also to identify key unsteady gas dynamic interactions occurring in the system. The results obtained allow for a better insight on the source and effect of different loss mechanisms occurring in the coupled PDC–turbine system. One key aspect arises from the interaction between the non-stationary PDC outflow and the constant rotor blade speed. Such interaction results in pronounced variations of rotor incidence angle, penalizing the turbine efficiency and capability of generating a quasi-steady shaft torque.

Numerical Prediction of a Radial Turbine Performance designed for Automotive Engines Turbocharger

These days the turbocharging system is assuming an essential part in enhancing car engines performance and diminishing fuel utilization and the fumes emanations, in spark-ignition and compression ignition engines. The performance of a radial turbine for the turbocharger device is heavily affected by the flow dynamics in a radial impeller. Furthermore, modification and improvement of a radial turbine impeller is a challenging task for turbomachinery engineers. Hence, this study aimed to further computational fluid dynamic analyses of a radial turbine stage performance .The design characteristics of a radial turbine stage, was used to simulate the flow by using independent packages of ANSYS CFX. The comparative study of a three dimensional flow simulation will give a more reasonable results of the turbine stage flow behavior and computational fluid dynamic simulation can give a more detailed result and reveal unexpected flow behavior like separation and vortexes.The results showed that the fluid flow dynamics within a turbine stage has indicated a noticeable performance characteristics. Obviously, it was observed that the pressure ratio and volume flow rate and efficiency were predicted numerically. Overall numerical results obtained from computational fluid dynamic simulations could produce a highly reliable for estimation on the performance a radial turbine of turbocharger.

Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds

The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the cavities below the hub level from the hot main annulus flow. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely, a high loading design case, and two high-speed points encompassing the peak efficiency. At each of these operating speeds, the amount of purge flow was varied from 0% to 2%. Observing the effect of the purge rate on measurement plane averaged parameters, a minor flow angle decrease and Mach number increase is seen for the low speed case, while maintaining near constant values for the higher operating speeds. The prominent effect due to purge is seen in the efficiency, showing a linear sensitivity to purge of 1.3%-points for every 1% of added purge flow for the investigated speeds. While spatial average values of flow angle and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible at higher span, with associated decreased turning. A radial efficiency distribution is utilized, showing negative impact through span heights from 15% to 70%. Pitchwise variation of investigated flow parameters is significantly influenced by purge flow, making this a parameter to include for instance when evaluating benefits of stator clocking positions.

Effect of Low-NOX Combustor Swirl Clocking on Intermediate Turbine Duct Vane Aerodynamics With an Upstream High Pressure Turbine Stage—An Experimental and Computational Study

Flow in an intermediate turbine duct (ITD) is highly complex, influenced by the upstream turbine stage flow structures, which include tip leakage flow and nonuniformities originating from the upstream high pressure turbine (HPT) vane and rotor. The complexity of the flow structures makes predicting them using numerical methods difficult, hence there exists a need for experimental validation. To evaluate the flow through an intermediate turbine duct including a turning vane, experiments were conducted in the Oxford Turbine Research Facility (OTRF). This is a short duration high speed test facility with a 3/4 engine-sized turbine, operating at the correct nondimensional parameters for aerodynamic and heat transfer measurements. The current configuration consists of a high pressure turbine stage and a downstream duct including a turning vane, for use in a counter-rotating turbine configuration. The facility has the ability to simulate low-NOx combustor swirl at the inlet to the turbine stage. This paper presents experimental aerodynamic results taken with three different turbine stage inlet conditions: a uniform inlet flow and two low-NOx swirl profiles (different clocking positions relative to the high pressure turbine vane). To further explain the flow through the 1.5 stage turbine, results from unsteady computational fluid dynamics (CFD) are included. The effect of varying the high pressure turbine vane inlet condition on the total pressure field through the 1.5 stage turbine, the intermediate turbine duct vane loading, and intermediate turbine duct exit condition are discussed and CFD results are compared with experimental data. The different inlet conditions are found to alter the flow exiting the high pressure turbine rotor. This is seen to have local effects on the intermediate turbine duct vane. With the current stator–stator vane count of 32-24, the effect of relative clocking between the two is found to have a larger effect on the aerodynamics in the intermediate turbine duct than the change in the high pressure turbine stage inlet condition. Given the severity of the low-NOx swirl profiles, this is perhaps surprising.

Numerical simulation of high-swirl flow in axial turbine stage

This article deals with numerical modelling of flow in an axial turbine stage with prismatic blades which are not equipped with shroud. In this case flow through a radial gap above and below ends of blades leads to generation of strong secondary vortices which significantly affect an effciency of the stage. The main attention is paid to turbulence modelling. Besides a linear model based on Boussinesq approximation a nonlinear model based on higher order closure formula is used. Also an effect of a curvature correction is taken into account.

EFFECTS OF VARYING TIP CLEARANCE AND AXIAL GAP ON AXIAL-FLOW TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

The leakage flow near the tip of rotor and stator blade rows of an axial-flow turbinestage imposes significant thermal loads on such blades. It is also responsible for theaerodynamic losses therein. This leakage flow is induced mainly by the pressuredifference across the tip section for both the rotor and the stator. Most research hashitherto focused on the effect of varying the tip clearance ratio, but a rather littleamount of published work on axial gap effect is found. This paper presents theoutcome of scanning the available research on tip clearance and axial gapparameters and effects of their variation on the flow characteristics andperformance of a typical axial–flow turbine stage. The prime objective here is tothrow some light upon the state of the art in this area of research. The surveyedliterature is discussed and criticized, giving suggestions for further investigation ofthe problem.

Investigation of flow in axial turbine stage without shroud-seal

This article deals with investigation of the influence of the radial gaps on the efficiency of the axial turbine stage. The investigation was carried out for the axial stage of the low-power turbine with the drum-type rotor without the shroud. In this configuration the flow through the radial gap under the hub-end of the stator blades and above the tip-end of the rotor blades leads to generation of the strong secondary flows, which decrease the efficiency of the stage. This problem was studied by experiment as well as by numerical modelling. The experiment was performed on the test rig equipped with the water brake dynamometer, torque meter and rotatable stator together with the linear probe manipulator. Numerical modelling was carried out for both the steady flow using the ”mixing plane” interface and the unsteady flow using the ”sliding mesh” interface between the stator and rotor wheels. The influence of the radial gap was studied in two configuration a) positive and b) negative overlapping of the tip-ends of the rotor blades. The efficiency of the axial stage in dependence on the expansion ratio, velocity ratio and the configuration as well as the details of the flow fields are presented in this paper.

The Mixed Modeling of the Steam Turbine Flow Characteristics Based on Improved Particle Swarm Optimization Level

Power station steam turbine stage flow characteristics show that the relationship between pressure and flow, which was the important research foundation for analysis of steam turbine performance and the further optimization analysis of unit. Based on strict theory analysis, this article obtained two important key characteristic coefficients such as the capacity of flow coefficient and the level of group critical pressure ratio which mainly influenced the turbine characteristics. And then the secondary flow calculation model was imposed combining with the massive actual data, adapting the method of improved PSO algorithm. The practical results show that, the obtained model not only ensured good regularity and ductility, but also has higher calculation precision.

Research of Flow Characteristics Hybrid Model of Steam Turbine Stage Based on the Improved PSO Algorithm

Power station steam turbine stage flow characteristics show the Corresponding relationship between pressure and flow rate, which is the important research foundation for analysis of steam turbine performance and the further optimization analysis of unit. Based on strict theory analysis, this article obtained two important key characteristic coefficients such as the capacity of flow coefficient and the level of group critical pressure ratio which mainly influenced the turbine characteristics. And then the secondary flow calculation model was imposed combining with the massive actual data, adapting the method of improved PSO algorithm. The practical results show that, the obtained model not only ensured good regularity and ductility, but also has higher calculation precision. DOI: http://dx.doi.org/10.11591/telkomnika.v11i11.3501 Full Text: PDF

Numerical study of blade deterioration effects on an industrial gas turbine stage performance and flow field

Turbine blades deteriorate over operation and overall performance of turbine decreases due to dust entry, fuel impurities, chemical reactions with air impurities, sulphur in the fuel, incomplete combustion and unburned carbon production. In this article, the effects of blade surface roughness and geometry changes caused by operation conditions on turbine performance were numerically calculated. Numerical calculations were carried out for the fourth stage of an axial turbine which was experimentally tested in the Technical University of Hannover, Germany. Results showed a good agreement with the previous measurements. To find out the effect of blade deteriorations on turbine stage performance and flow field, blade deteriorations including blade surface roughness, tip clearance increment and fouling on vane and blade of turbine were applied in four different mass flow rates to the three-dimensional numerical model.

0404 単段タービン内部流れ場の非定常性及びパージ空気噴出しが空力性能に与える影響に関する研究(OS4-1 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

This paper presents experimental and numerical simulation study of single turbine stage flow field with injected purge air. To investigate the influence of the purge air from the Rim-seal cavity, we conducted 5-Hole probe and Slant-type hot wire probe traverse measurement downstream of the rotor blade. Those measurement results were used to validate the numerical simulation data then we described the flow field of the rotor passage and cavity domain. In the case of injected purge air, Rim-seal cavity flow field tend to non-uniform and we observed unsteady vorticity distribution around cavity outlet. Those flow filed entrained streamwise vorticity and entropy generation rate in the rotor passage.

Simulation of a 3D unsteady flow in an axial turbine stage

The contribution deals with a numerical simulation of an unsteady flow in an axial turbine stage. The solution is performed using an in-house numerical code developed in the Aeronautical and Test Institute, Plc. in Prague. The numerical code is based on a finite volume discretization of governing equations (Favre aver- aged Navier-Stokes equations) and a two-equations turbulence model. The temporal integration is based on the implicit second-order backward Euler formula, which is realized through the iteration process in dual time. The proposed numerical method is used for solution of the 3D, unsteady, viscous turbulent flow of a perfect gas in the axial turbine stage. The flow path consists of an input nozzle, stator blade-wheel, blade-wheel, a shroud-seal gap and a diffuser. Attention is paid to the influence of a secondary flow structures, such as generated vortices and flow in shroud-seal gap. 1I NTRODUCTION The aim of this study is to investigate some properties of flow field in the axial turbine stage. At first the flow in the turbine stage was modeled in the middle section of the turbine stage as the two-dimensional turbulent unsteady flow. Furthermore, a calculation of the three-dimensional unsteady inviscid flow was performed. Boundary phenomena - secondary flow - have been studied using model of the three- dimensional steady turbulent flow, using the frozen rotor technique. Effect of the secondary flow through the seal of the was studied in a simplified model of a prismatic blade cascade using model of the three-dimensional steady turbulent flow. The turbine stage consists of the stator and wheels. The stator wheel contains 70 and the wheel 90 blades. Therefor it was possible consider only periodic field of seven stator and nine blades for the calculation. The hub diameter of the stage is 0.506 m, the tip diameter is 0.597 m (blades span is 0.0455 m), the axial chord of the stator is 0.01955 m, the axial chord of the is 0.025 m (both at the hub), the gap between stator and is 0.005 m. The shape of the blades is shown in Figure 1. The angular speed of the is 455.11 rad s −1 . The inlet total pressure is 1.311 · 10 5 Pa, the inlet total temperature is 55.81 ◦ C, the angle of attac is 0 ◦ and the outlet static pressure is 0.9538 · 10 5 Pa. The in-house URANS numerical code was developed for calculation of flow in the turbine stage.

Investigation of unsteady flow in axial turbine stage

The never ending process to increase the efficiency of turbine stages introduced an idea to create an axial turbine stage test rig as part of closed loop transonic wind tunnel at Vyzkumny a zkusebni letecky ustav (VZLU). Studying of unsteady flow field behaviours in turbine stages is nowadays essential in the development process. Therefore, the test rig was designed with focusing on possibility of detailed studying of unsteady flow fields in turbine stages. New methodologies and new instrumentations were developed at VZLU and successfully integrated to gain valuable information from experiments with turbine stages. Two different turbine stages were tested during the facility introduction process. The measurement of these two models demonstrated how flexible the test rig is. One of them was an enlarged model of small gas turbine stage. The other was scaled-down model of stage of intermediate-pressure steam turbine. The external characteristics of both models were acquired during experiments as well as the detailed unsteady flow field measurement. Turbine stages were tested in various regimes in order to check the capabilities of the facility, methodology and instrumentation together. The paper presents results of unsteady flow field investigation in the enlarged turbine stage with unshrouded rotor. The interaction of structures developed in a stator with the rotor flow field is depicted and the influence of turbine load on evolution of secondary flows in rotor is analysed.

Numerical modeling of unsteady flow in steam turbine stage

This work deals with numerical solution of unsteady flow in turbine stage. We use models of compressible single-phase flow of air and two-phase flow of wet steam. Presented numerical methods are based on different stator-rotor matching algorithms, as well as different numerical schemes. Numerical results achieved by both methods and flow models are discussed.

J0501-2-2 軸流タービン空力性能に及ぼす動静翼間距離の影響(流体機械の研究開発におけるEFD/CFD(2))

The purpose of this study is to investigate the effects of the axial gap between stator and rotor upon the performance and secondary flow field of a single axial flow turbine stage. We performed experiments for three axial gaps. In our test rig, it is possible to change the axial gap by moving the stator vane in axial direction. The tests were carried out at two different conditions, that is design and off-design conditions. The unsteady three-dimensional flow field was analyzed by time-accurate RANS (Reynolds-Averaged Navier-Stokes) simulations. The simulation results were compared with the experiments, in which total pressure loss and time-averaged flow field upstream and downstream of the rotor were obtained by five-hole probe measurements. The effect of the axial gap was confirmed in the endwall regions, and obtained relatively at the off-design condition. The turbine stage efficiency was improved almost linearly to reduce the axial gap at the off-design condition.