Axial Turbine Stage Research Articles

Upgrading the Compressor Stage of the CAT250TJ Micro Gas Turbine Engine

AbstractDue to their simplicity and relative ease of manufacture, single-stage centrifugal and mixed flow micro gas turbine (MGT) engines are preferred in thrust-based remotely piloted aerial vehicles. A single-stage mixed-flow compressor upgrade for the 200 N CAT250TJ MGT engine is numerically evaluated and presented. An in-house developed mean line application and commercial CFD software is used for the design and performance evaluation of the proposed upgrade configurations. The CAT250TJ – Gen1 engine features a single-stage centrifugal compressor, annular combustor, and single stage axial turbine. Apart from an upgraded impeller, a new crossover diffuser configuration is introduced to replace the wedge-type, straight outlet diffuser configuration of the Gen1 engine. The new single vane crossover diffuser configuration provides a design point total-to-total efficiency and pressure ratio increase of 8.3% and 12.1%, respectively. A disadvantage of a single-vaned crossover diffuser compared to legacy diffusers is a narrower operating range. To alleviate this issue, various combinations of tandem and splitter vane crossover diffuser configurations are proposed. These provide an enhanced operating range, comparable with the operating range displayed by the Gen1 configuration. A turbine power matching analysis is additionally completed to ensure proper compressor integration. Gas turbine cycle software is used to evaluate the on-engine performance of the upgraded compressor configurations. It is shown that the new baseline, single vane crossover diffuser configuration provides a 10.74% increase in design point static thrust.

Noise Mechanisms of an Axial Turbine Stage Based on Large Eddy Simulation

Noise Mechanisms of an Axial Turbine Stage Based on Large Eddy Simulation

CFD Analysis of an Aircraft Turbofan Engine Combustion Process and the Effect on Turbine

In this paper, a two-dimensional computational fluid dynamics (CFD) study of Turbofan engine is presented using the ANSYS Fluent program, the navier–stokes equations is used for analysis, including a two-dimensional and symmetrical drawing of both the combustion chamber and in a 1.5 Stage Axial Flow Turbine. A GE-90 turbofan engine nacelle was used with Naca 63-412 type blades were used for the analysis of the flow on the turbine blades. Combustion chamber simulations were carried out using a previous study. The computational results were compared with other studies on the Exergetic analysis of a GE-21 turbojet engine. The GE-21 engine had a combustion chamber temperature of 2900 K, while the GE-90 engine had a temperature of around 2706 K. The previous study considered the velocity of fluid flow to be 200 m/s, whereas the velocity of flow in this study was 209 m/s as determined in the part of analysis and result.

The Results of Calculations of the Axial Turbine Stage with Different Meridional Outlines of Its Adjustable Nozzle Vane

Turbomachines with adjustable (rotary) nozzle vanes (ANV) find increasingly broader use in various technical fields owing to their featuring lower loss of efficiency in comparison with other flow rate changing methods. Improvement of their efficiency is becoming more important while fulfilling the manufacturability and reliability requirements. Three options for shaping the meridional outlines of the adjustable nozzle vane (ANV) and the blades themselves, which are rather complex items for manufacture, are studied by calculation: option 1 – with conventional cylindrical meridional surfaces and blades cut at the ends with spherical surfaces, which ensure an acceptable (around 0.3 mm) minimum tip clearance above the leading and trailing edges only at the smallest of the possible blade angles, and in the root section – only at the maximum blade angle (of the required range); option 2 – with spherical outlines and blades cut along a sphere equidistant to the outline spheres (with a clearance of around 0.3 mm); option 3 – with flat meridional outlines in the form of a polyhedral prism and blades with flat ends equidistant to the prism faces (with a clearance of around 0.3 mm); The results of calculations carried out in the ANSYS CFX software package are described and analyzed, which have shown a slight advantage in efficiency ηri (by around 2%) for options 2 and 3. For these options, the decrease in efficiency with an increase in the flowrate above its design value is less noticeable than for option 1, and with flowrates lower than the design one, the values of efficiency ηri are the same for all options.

CFD Analysis of a Transient Rotor-Stator Axial Steam Turbine Stage

An axial steam turbine stage has both stationary and rotating components, which are coupled together in a CFD model by multiple frames of reference. There are three types of interface techniques available to exchange the information between the different frames of reference namely frozen rotor, stage, transient stator rotor. Both frozen rotor and stage interfaces are used in steady state analysis. The operation of axial turbine is inherently an unsteady process. The aerodynamic interaction between the rotating part and the stationary parts are the important contributor to the unsteadiness of the flow present in the turbine. Neither of the two interfaces implemented in the steady state CFD analysis is capable of predicting the unsteady effects resulting from the rotor-stator interaction due to their relative position change. The third type of interface, the transient stator-rotor interface, is available to simulate the fluid motion caused by the relative movement between a rotor and stationary components in axial turbine. Although enormous computer resources are needed for this modelling, it simulates real flow physics best of all, while steady or quasi-steady numerical approaches only approximate the real flow, because they neglect important effects of blade row interactions. The paper presents the CFD analysis carried out for an axial steam turbine stage with three different interface techniques and compares the results.

Investigation of the stress-strain state of a turbine blade twisted according to the potential vortex law by the finite element method

Increase of power and complication of turbomachinery design is accompanied by stricter requirements to their reliability. Increasing the service life of turbomachinery is also one of the main tasks of quality improvement. Since the blade is a highly loaded element of any turbomachine, high operational requirements are imposed on it, expressed in reliability and durability of this element. A large number of factors affect the performance of the blade, one of which is its twist. The purpose of the current study is to determine the effect of twist of a gas turbine blade twisted according to the potential vortex law.The results of research of twist law influence on stress-strain state of the blade of the last stage of axial gas turbine, twisted according to the potential vortex laware presented. For this purpose, using the internal packages Ansys, CFX and Static Structural, we performed an interdisciplinary conjugate analysis of the solutions of the computational gas dynamics and static strength problems. During the analysis of the static strength problem we considered the tensile stresses arising in the field of centrifugal forces, bending stress (in different planes — from the pressure difference between inlet and outlet and from the pressure difference on the concave and convex surfaces of the blade), torsional stress, as well as thermal stress.Evaluation of the obtained results in conjunction with the analysis of previously derived analytical dependencies allowed to establish the influence of blade twist on the stress-strain state. The factor of torsion stresses and deformations should be taken into account when designing twisted blades and their subsequent gas-dynamic and strength estimation.

Multi-objective optimization of the ORC axial turbine for a waste heat recovery system working in two modes: cogeneration and condensation

Due to the demand of the district heating network and electric power grid ORC turbines can operate in the condensation and cogeneration modes. This approach requires the design of an expander which is characterized by high efficiency in each mode of operation. The paper is devoted to a multi-objective efficiency optimization of a one stage axial ORC turbine working on MM (Hexamethyldisiloxane). An Implicit Filtering algorithm (IF) is used to find a flowpath with maximum efficiency. During the optimization the rotor profiles (at the hub and shroud) and the shape of endwall contours of the rotor domain are changed. Five optimization tasks are carried out with different weights of the efficiency of both modes of operation. Pareto fronts are obtained and a decision-making method is used to select an optimum solution. The optimization of the rotor row allows for significant efficiency improvements in two regimes of operation, with respect to a baseline geometric configuration designed with the help of classical methods.

On Dynamics of Flow past a Stage Axial Air Turbine

The air flow inside a single-stage test turbine is studied experimentally using the Particle Image Velocimetry technique. The measurements were performed at the axial-tangential plane just behind the rotor at the middle blade radius. The large vortical structures are identified in the shear layers between the blade wakes and channel jet. The phase-locked structures topology of random dynamical structures in the flow behind the stage are to be analysed using the Proper Orthogonal Decomposition method.

Estimation of the Induced Incidence of a High Reaction Axial Turbine Bucket

This paper describes the effect of the incidence angle of the bucket on the performance of the axial turbine stage. The off-design operating conditions of the turbine stage result in a change in the velocity diagrams. This results in a positive or negative incidence. One of the basic objectives in turbine stage design is to estimate the flow behaviour of the turbine stage during off-design operation as accurately as possible and to quantify the corresponding decrease in efficiency. The available loss prediction models allow the estimation of the loss distribution when the incidence angle changes in the preliminary design phase. However, the incidence angle is actually affected by the velocity of circulation, which changes the input velocity vector (induced incidence). Thus, the blade row angle of attack is different from the angle based on the velocity diagram calculations. The result of our paper is a relation for estimating the angular difference of the input flow angle to the bucket defined as a function of the turbine operation mode.

A parametric study of squealer tip geometries applied in a hydraulic axial turbine used in a rocket engine turbopump

Axial turbines are machines widely used in different engineering applications. Due to their constructive characteristics, they must have a space between the rotor blades and the turbine casing, called tip clearance. Unfortunately, this gap allows a part of the fluid to leak from the pressure side to the suction side of the rotor blades. This leakage is undesirable and represents an energy loss. A way to avoid part of this loss is through the use of desensitization techniques. Although the use of these techniques is widely known, no studies in the open literature have evaluated these techniques in hydraulic turbines. This work presents a numerical analysis of squealer desensitization techniques applied in a hydraulic axial turbine. The turbomachine under study is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME). Numerical simulations were performed using CFX v.19.2 software, and computational meshes were generated in ICEM v.19.2 software. Initially, the computational model was validated, using the experimental results published by the National Aeronautics and Space Administration (NASA). A parametric analysis was performed considering the variation in squealer cavity depth and rim thickness. The study found that the squealer cavity depth has a greater influence on the stage performance than its rim thickness. The tendency is that the greater the cavity depth, the greater the stage efficiency. One of the squealer geometries analyzed allowed an average increased efficiency of 1.43%, over the entire turbine operational range. The results obtained also show that the application of the proposed geometries would enable the reduction in cavitation close to the trailing edge of the rotor blades. This result is extremely valuable, as it can impact the life cycle of the turbine.

Experimental Evaluation of Axial Reaction Turbine Stage Bucket Losses

The article describes the measurement methods and data evaluation from a single-stage axial turbine with high reaction (50%). Four operating modes of the turbine were selected, in which the wake traversing behind nozzle and bucket with five-hole pneumatic probes took place. The article further focuses on the evaluation of bucket losses for all four measured operating modes, including the analysis of measurement uncertainties.

Impact of Swirling Entropy Waves on a High Pressure Turbine

AbstractThe harsh environment exiting modern gas turbine combustion chamber is characterized by vorticity and temperature perturbations, the latter commonly referred as entropy waves. The interaction of these unsteadiness with the first turbine stage causes non-negligible effects on the aerodynamic performance, blade cooling, and noise production. The first of these drawbacks is addressed in this paper by means of an experimental campaign: entropy waves and swirl profile are injected upstream of an axial turbine stage through a novel combustor simulator. Two injection positions and different inlet conditions are considered. Steady and unsteady experimental measurements are carried out through the stage to address the combustor-turbine interaction characterizing the injected disturbance, the nozzle, and rotor outlet aerothermal field. The experimental outcomes show a severe reduction of the temperature perturbation already at stator outlet. The generated swirl profile influences significantly the aerodynamic, as it interacts with the stator and rotor secondary flows and wakes. Furthermore, the clocking position changes the region most affected by the disturbance, showing a potential modifying the injection position to minimize the entropy wave and swirl profile impact on the stage. Finally, this work shows that in order to proficiently study entropy waves, the unsteady aerodynamic flow field stator downstream has to be addressed.

Систематизация математических зависимостей для оценки вентиляционных потерь мощности в осевой турбинной ступени, в цилиндре, в паровой турбине

In the world practice of steam turbine construction, dozens of different, usually empirical mathematical dependencies (formulas) have been used to calculate ventilation power losses in the axial turbine stage. The formulas cover a wide range of parameters that affect the amount of ventilation losses. There is a significant error in calculations relative to experimental data for specific types of turbines. The comparative analysis of the known formulas allowed us to group the dependencies properly and identify the boundaries of their appropriate application, to establish those of them, the calculations for which lead to minimal errors relative to the experimental data, as well as to identify a formula that can be used to determine ventilation heating. The interest in ventilation modes of operation of TPP steam turbines is caused by the need to increase the efficiency of equipment due to the increasing cost of organic fuel and further expansion of combined generation of electricity and heat, related to solving the problem of converting powerful heating turbines to three-stage heating of network water, searching for rational operation of the Central heating system during periods of failures of electric load schedules and implementing specific operating modes, such as motor mode, the need to ensure high maneuverability of the equipment of power units, TPP, power units in whole. At the same time, the problem of ensuring the systematic deepest discharge of the TPP during the night failure of the electrical load schedule [1-3]; increasing the number of cases of forced operation of the condensing unit with increased pressure, described in [4, 5], is put forward as a number of priorities. Reducing heat losses in the condenser and increasing the share of electricity generated by heat consumption is the main direction of improving the efficiency of heating turbines. The solution of these problems is mainly related to the organization of the most economical operation modes of steam turbines Central heating system. In the operation modes of start-stop, idle, emergency load relief, heating, motor, hot rotating reserve, the characteristics of the turbine spade device are entirely determined by the influence of ventilation phenomena that occur and flow in the flow part of the cylinder (ventilation power losses) [3], ventilation heats [6], intense excitation of bending-torsional axial resonant vibrations by a screw flow of working steam pulsating with a frequency of, equal to the speed of rotation of the ventilation flow in the gap between the diaphragm and the grid of the working blades in the range of 0.560-0.572 of the shaft speed, due to the regular impact of uneven rotating ventilation flow by alternately stretching and compressing the passage section of the working steam flow, and can lead to failure of the working blades [7].

Development of a generalized physical and mathematical model of working substance processes in an axial turbine stage

Methods of continuum mechanics and equilibrium thermodynamics are used to study a generalized physical and mathematical model of the processes of a working substance (steam, gas) moving in the flow part of an axial turbine stage in the nominal operating mode of the turbine. The mathematical description of the hydrodynamics and thermodynamics of the process is carried out for a one-dimensional model, based on the energy equation in thermomechanical form (the first law of thermodynamics in combination with the Bernoulli equation) for the gas (or steam) flow during its adiabatic (isentropic) expansion in the direction of the axis of the turbine stage. The energy equation is written taking into account both thermodynamic (due to the thermal movement of particles) and hydraulic pressure forces (due to the mechanical action of a continuous medium) of the working substance flow on the walls of the stage flow channel. Numerical calculation of flow rates and enthalpy losses on various elements of the stage (nozzle and working blades) is performed on the example of a model turbine with eight axial-type stages, under specified initial conditions of the process.

Numerical investigation of non-uniform flow in twin-silo combustors and impact on axial turbine stage performance

A clear understanding of the flow characteristics in the older generation of industrial gas turbines operating with silo combustors is important for potential upgrades. Non-uniformities in the form of circumferential and radial variations in internal flow properties can have a significant impact on the gas turbine stage performance and durability. This paper presents a comprehensive study of the underlying internal flow features involved in the advent of non-uniformities from twin-silo combustors and their propagation through a single axial turbine stage of the Siemens v94.2 industrial gas turbine. Results indicate the formation of strong vortical structures alongside large temperature, pressure, velocity, and flow angle deviations that are mostly located in the top and bottom sections of the turbine stage caused by the excessive flow turning in the upstream tandem silo combustors. A favorable validation of the simulated exhaust gas temperature (EGT) profile is also achieved via comparison with the measured data. A drop in isentropic efficiency and power output equivalent to 2.28% points and 2.1 MW, respectively is observed at baseload compared to an ideal straight hot gas path reference case. Furthermore, the analysis of internal flow topography identifies the underperforming turbine blading due to the upstream non-uniformities. The findings not only have implications for the turbine aerothermodynamic design, but also the combustor layout from a repowering perspective.

Design Guidelines for Axial Turbines Operating With Non-Ideal Compressible Flows

Abstract The impact of non-ideal compressible flows on the fluid-dynamic design of axial turbine stages is examined. First, the classical similarity equation (CSE) is revised and extended to account for the effect of flow non-ideality. Then, the influence of the most relevant design parameters is investigated through the application of a dimensionless turbine stage model embedding a first-principles loss model. The results show that compressibility effects induced by the fluid molecular complexity and the stage volumetric flow ratio produce an offset in the efficiency trends and in the optimal stage layout. Furthermore, flow non-ideality can lead to either an increase or a decrease of stage efficiency up to 3–4% relative to turbines designed to operate in dilute gas state. This effect can be predicted at preliminary design phase through the evaluation of the isentropic pressure–volume exponent. Three-dimensional (3D) RANS simulations of selected test cases corroborate the trends predicted with the reduced-order turbine stage model. URANS computations provide equivalent trends, except for case study niMM1, featuring a non-monotonic variation of the generalized isentropic exponent. For such turbine stage, the efficiency is predicted to be higher than the one computed with any steady-state model based on the control volume approach.

Determination of the Idle Mode of the Stage of Axial Turbine during Operation at Partial Loads

On the basis of the one-dimensional theory of calculating the operation of steam turbine stages the method for determining the idle mode, the initial data for which are the geometric characteristics of the blade rows is proposed. Formulas have been obtained that make it possible to calculate the efficiency in the proximity of Rotor Blades (RB) at operating modes from nominal to the idle mode, depending on the flow rate of the stage and taking into account the use of kinetic energy with the runaway velocity and losses arising at off-design angles of flow on the Rotor Blade (RB). The results of possible computational studies and their comparison for an incompressible working fluid with the results of experimental studies showed the good possibilities of the proposed method for determining the idle mode in a wide range of the characteristics of stages.

Numerical Three-Dimensional Simulation of Gas Dynamic Processes in the Stage of a Small-Sized Ultra-Low Power Axial Turbine

The problems of creation and calculation of virtual numerical models in the stage of an ultra-low power axial turbine are considered. A method for constructing the calculation area of the flow in an axial turbine and a finite element grid superimposed on this area is given. The characteristics of the power efficiency and specific power of the turbine are obtained depending on the pressure ratio and the loading parameter. The results of the numerical experiment are verified with the data of the full scale experiment.

On the far-field boundary condition treatment in the framework of aeromechanical computations using ANSYS CFX

This numerical study aims at predicting the reflective behavior of different conventional inlet and outlet far-field boundary conditions as well as available non-reflecting boundary conditions (NRBC) implemented in the commercial CFD solver ANSYS CFX. An isolated rotor model of an axial turbine stage with prescribed blade displacement is applied as test case to consider a representative application case, while at the same time provoke an unsteady flow field featuring pronounced flow perturbations in the far-field. Since the reflective behavior of the implemented boundary conditions was found inadequate in the given application case, a zonal treatment of the inlet and outlet far-field, based on a modification of the governing Navier-Stokes equations, is investigated. The applied approach has proven its capability to suppress spurious reflections reliably, while at the same time ensures a preservation of the reference flow conditions within the required domain extensions. The results of a case study considering calculation domains of different spatial extent and different treatments of their respective far-fields suggest variations in the steady flow aerodynamics to be of moderate influence on the predicted aerodynamic damping, while spurious reflections were found to falsify the unsteady aerodynamics considerably.

Fully-turbulent adjoint method for the unsteady shape optimization of multi-row turbomachinery

The possibility of taking into account unsteady flow effects if performing turbomachinery shape optimization is attractive to accurately address inherently time dependent design problems. The harmonic balance method is an efficient solution for computational fluid dynamics problems of turbomachinery characterized by quasi-periodic flows. If applied in combination with adjoint methods, it enables the possibility to deal with unsteady fluid-dynamic design in a cost effective manner, opening the way towards multi-disciplinary applications. This paper presents the development of a novel fully-turbulent discrete adjoint based on the time domain harmonic balance method and its application to the constrained fluid dynamic optimization of an axial turbine stage. As opposed to previous works, the proposed method does not require any assumption on the turbulent eddy viscosity and on the set of input frequencies. The results show that the method provides accurate gradients, if compared with second order finite differences, and significant deviation with respect to the sensitivity computed with the constant eddy viscosity approximation. The application of the method to the fluid-dynamic shape optimization of the exemplary stage leads to improve the total-to-static efficiency of 0.8%. The efficiency increase is found to be higher than that obtained by means of a steady state optimization method.