Radial Turbomachines Research Articles

Numerical Study of the Strength Radial Turbomachines Based on the Use of Stainless Steel 316L

By studying various properties of materials came to the conclusion that stainless steel 316L has good properties. This material is suitable for making radial wheel turbines compared to other materials. The object of the study is a radial wheel with 10 blades manufactured by “Schiele” (Germany), which specializes in the production of units for the chemical industry and ventilation equipment. The finite element method was chosen as the basic research method for solving problems of natural and forced vibrations, static stress and studying the degree of reactivity blades radial wheels of turbomachines. It can be argued that the numerical analysis of the strength characteristics of heavily loaded turbine elements with the help of electronic computers provides a greater depth of research, the breadth of the issues covered, significantly reduces the amount of expensive experimental research, reduces the time for designing new turbines in terms of efficiency, reliability, technology and resource saving of highly loaded units. In this paper, calculations were made of the characteristics of natural frequencies, equivalent stresses, deformation and the degree of reactivity blades when using material stainless steel 316L. It is noted that this material provides the criterion of stress concentration in the wheel as low as possible and the natural frequencies of the wheel are reduced, but it does not lead to a change in the oscillation modes of this wheel. So 316L stainless steel is recommended for evaluating options in the manufacture of this radial wheel of turbomachines in the field of power, chemical and transport engineering.

A Method for Predicting the Aeroelastic Response of Radial Turbomachines

AbstractAircraft intermittent combustion engines often incorporate turbochargers adapted from ground-based applications to improve their efficiency and performance. These turbochargers can operate at off-design conditions and experience blade failures brought on by aerodynamic-induced blade resonances. A reduced-order model of the aeroelastic response of general fluid–structural configurations is developed using the Euler–Lagrange equation informed by numerical data from uncoupled computational fluid dynamic (CFD) and computational structural dynamic calculations. The structural response is derived from a method of assumed-modes approach. The unsteady fluid response is described by a modified version of piston theory that approximates the local transient pressure fluctuation in conjunction with steady CFD solution data. The reduced-order model is first applied to a classical panel flutter scenario and found to predict a flutter boundary that compares favorably to the boundary identified by existing theory and experimental data. The model is then applied to the high-pressure turbine of a dual-stage turbocharger. The model predictions are shown to reliably determine the lack of turbine blade flutter and rudimentary damping comparisons are performed to assess the ability of the model to ascertain the susceptibility of the turbine to forced response. Obstacles associated with the current experimental state of the art that impinge upon further numerical validation are discussed.

Assessment of closed cycles operating with supercritical CO2 as bottoming of small combustion turbines

This work investigates the performance of supercritical CO2 power cycles bottoming small combustion turbines. As a matter of fact, the maximum power output of the topping cycle is limited to 10 MW, since there is a great number of commercial combustion turbine units for which the conventional combined cycle architecture with a bottoming steam power plant is not convenient. In detail, the partial heating cycle is the layout chosen for this study according to the interesting trade-off between heat recovery and cycle efficiency, with a limited number of components. Considering the investigated range of power production, single-stage radial turbomachines are selected and their efficiency values are not fixed at first glance but result from actual size and running conditions, based on flow rates, enthalpy variations as well as rotational speeds. Focusing on a number of cases, interesting considerations about the size of the components of the supercritical CO2 power cycle are possible thanks to the theory of similitude.

Techno-economic investigations of supercritical CO2-based partial heating cycle as bottoming system of a small gas turbine

Supercritical CO2 (sCO2) cycles represent an innovative technology especially if applied for waste heat recovery from gas turbines. This work investigates the performance of the partial heating sCO2 cycle as the bottoming cycle of a 5 MW-class gas turbine. Particular attention is paid to the selection of both minimum CO2 pressure and temperature and use of the non-dimensional criterion named Acceleration Margin to Condensation is made to prevent the formation of liquid CO2 droplets at the inlet of the compressor. Moreover, in order to avoid heavily loaded turbomachinery, considerations about the machine Mach numbers result in possible limits for the maximum cycle pressure. Single-stage radial turbomachines are selected and their efficiency calculated according to Aungier's correlations by taking actual size and running conditions into account. Focusing on the net electric power produced by the bottoming cycle and on the corresponding specific cost, a number of investigations has been carried out. After setting a limit for the compressor Mach number, around 1600 kW can be recovered by the sCO2 bottoming cycle, though a techno-economic optimization would guide towards an optimum point with slightly more than 1500 kW of power output and a specific cost for the technology of around 2000 $/kW.

Transient separation and fluctuation of turbulent flow in an axisymmetric U-turn channel perturbed by periodically passing gust inflow

The flow in the vane-less diffuser bend and return the channel of radial turbo-machines which is perturbed by the time-periodic and circumferentially passing jet-wake structure exited from the upstream impeller, and the transient characteristics of separation and fluctuation occurring in these stationary components determine the operational stability and performances of the turbo-machines especially for the next stage. In this work, we present a numerical investigation on the transient separation and fluctuation behaviors of turbulent flow in a sector of a 180° bended axisymmetric U-turn channel subjected to time-periodic gust inflow which passes in the circumferential direction. The objective is to explore the effect of period of gust inflow, in simulating the non-dimensional blade passing frequency (BPF*) in turbo-machines, on the characteristics of flow in the whole U-turn channel. Numerical results reveal that flow separation occurs in the curved section for about half the cycle at BPF* = 1 and 2, and earlier separation is observed for BPF* = 2, while there is no separation for BPF* = 5 and 10. There is a phase lag between the local skin friction coefficient in the channel and gust inflow, and the magnitude of the phase lag is related to BPF*. As BPF* increases, the thickness of the boundary layer on both walls decreases.

Fatigue life of radial turbomachines at changing thickness blades taking into account intentional mistuning

Fatigue life of radial turbomachines at changing thickness blades taking into account intentional mistuning

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ И ЧИСЛЕННАЯ ОЦЕНКА ДОЛГОВЕЧНОСТИ РАДИАЛЬНЫХ РАБОЧИХ КОЛЕС ТУРБОМАШИН

The radial blade discs are nominally designed to be cyclically symmetrical. But the vibration characteristics of all the ra-dial blades on the disc are slightly different due to manufacturing tolerances, variations in material properties and wear during operation. These small changes break the cyclic symmetry, break the pairs of eigenvalues and affect the durability of the radial impellers of turbomachines. In further work, the designs of such systems may fail before the estimated resource or service life. Therefore, when designing, manufacturing, and operating turbomachines, it is necessary to understand the effect of parameter mistuning to manage the resource and ensure the required level of strength, reliability, and durability of radial turbomachines. This study proposes a technique for mathematical modeling and prediction of high-cycle fatigue life of radial wheels tur-bines, taking into account dynamic loading. Numerical assessment of durability was performed on the example of a radial wheel with 10 blades manufactured by Schiele (Germany). The results were obtained when calculating the dynamic load in the MATLAB program and high-cycle fatigue in the ANSYS program.

Numerical investigation on separated turbulent flow in a three-dimensional U-turn duct with spanwise diverging

The flow in a U-turn duct with a 180-degree curved section is a typical model of various applications such as the bend and return channel in multi-stage radial turbo-machines. The flow exhibits complex patterns including the separation on the inner wall, highly sheared flow in the curved and downstream sections, and recovery of deficit flow to uniform flow. Most of current researches focus on the simplified models of two-dimensional plane duct or three-dimensional duct with constant cross-section, while in realistic circumstances the duct can be varying in the shape and area of the cross-section to meet the design requirement. In this work, we performed a numerical investigation on the turbulent flow in a U-turn duct with spanwise diverging at Reynolds number Re = 106. The effect of diverging, as represented by the height of the duct, on the formation of secondary flow, flow separation and recovery is explored, and the three-dimensionality of the separated flow is quantitatively assessed. Numerical results reveal that with stronger spanwise diverging, the flow separates earlier from the inner wall and the size of the separated vortex is larger; the primary characteristics of the secondary flow also change significantly. The three-dimensional separated flow substantially affects the flow in the downstream straight duct that both streamwise and radial velocities exhibit fluctuating patterns as a result of the spatially non-uniform separation. The characteristics of boundary layer flow on all solid walls are also analyzed and discussed regarding the pressure field and local shearing.

Experimental Fluid Dynamics Applications in Radial Turbomachines: Inlet Recirculation in Centrifugal Compressor, Rotating Stall and Flow in Vaneless Diffuser, and Improvement in Accuracy of CFD for Predicting Flow Fields in a Radial Turbine Rotor

Performance of a turbomachine strongly depends on its internal flow. CFD (Computational Fluid Dynamics) is now an essential tool obtaining information on such internal flow as well as its performance. However, when CFD is taken into a design process, the accuracy and feature of a CFD code must be understood. CFD requires EFD (Experimental Fluid Dynamics) for validating and ensuring its accuracy. Besides, EFD provides some empirical rules and models to complex phenomena that CFD needs high computational costs and long turnaround time and that are difficult to be integrated in a design work. Since CFD and EFD are complementary to each other, EFD with CFD or CFD with EFD serves as a powerful tool to understand flow phenomena in turbomachines. So, EFD is still important and frequently applied in industries to design and develop radial turbomachines. Examples of EFD conducted during the design of centrifugal compressors and radial turbines in the author’s affiliation are introduced here.

Thermo-economic analysis of a supercritical CO2-based waste heat recovery system

This work investigates the performance of a supercritical CO2cycle as the bottoming cycle of a commercial gas turbine with 4.7 MW of electric power output. In detail, the partial heating cycle is the layout chosen for the interesting trade-off between heat recovery and cycle efficiency with a limited number of components. Single-stage radial turbomachines are selected according to the theory of similitude. In particular, the compressor is a troublesome turbomachine as it works near the critical point where significant variations of the CO2properties occur. Efficiency values for turbomachinery are not fixed at first glance but result from actual size and running conditions, based on flow rates, enthalpy variations as well as rotational speeds. In addition, a limit is set for the machine Mach numbers in order to avoid heavily loaded turbomachinery. The thermodynamic study of the bottoming cycle is carried out by means of the mass and energy balance equations. A parametric analysis is carried out with particular attention to a number of specific parameters. Considering the power output calculated for the supercritical CO2cycle, economic calculations are also carried out and the related costs compared to those specific of organic Rankine cycles with similar power output.

Limiting state of turbomachine disks under conditions of high-intensity thermal changes

The article considers specific features and computing methods for a number of limiting inelastic states of disks of axial and radial turbomachines under low-cycle loadings with great temperature stresses decreasing the bearing capacity due to deformation mechanisms qualitatively different from those observed with weak thermal changes.

First Russian long length HTS power cable

The Russian R&D Program for superconducting power devices is underway, supported both by government and electric power companies. In this program R&D on HTS power cables is considered as most advanced and close to commercialization. In the framework of the program, several, heavily instrumented, 5m cables have been tested following by the 30m – 3 phase experimental power cable development and testing in 2008–2009. The latest achievement is development and testing of the first long length 3×200m power cable with rating 1.5/2kA–20kV. In parallel with just the cable development the innovative cryogenic system has been developed as well for the cable cooling. The system is using neon as working substance and radial turbo-machines in refrigerator. Cooling power is up to ∼8kW at 65K, inter-maintenance time ∼30,000h. The cryogenic pump with superconducting motor can be used to provide subcooled liquid nitrogen flow ∼0.1–1.5kg/s at 0.1–2.5MPa pressure. After extensive tests at special test facility, HTS power cable and cryogenic system are planning to be installed at some substation in Moscow utility grid. In this review some details about Russian HTS power application program, 200m cable and cryogenic system designs and tests results are presented.

Comparison of turbulence methods in CFD analysis of compressible flows in radial turbomachines

PurposeThe purpose of this paper is to show the superior turbulence method in CFD analysis of radial turbo machines and to introduce the best way to choose turbulence parameters whenever FLUENT user applies this software as a complementary design tool for high‐speed turbo machinery components.Design/methodology/approachOne of the most important issues in CFD is analysis of flow field in turbo machines. Flow in high‐speed radial turbo machinery is a 3D, turbulent and unsteady behavior so needs suitable method for converging. It is clear that the turbulence model has an extraordinary effect on investigation of 3D flows in high‐speed turbo machinery. A centrifugal compressor of micro and radial turbines have been designed and simulated 3D using the commercial CFD‐code FLUENT 6. Three turbulence models k‐ε/standard, renormalization‐group (RNG) and RSM were considered and results of three models were compared with experimental and 1D design results.FindingsThe study showed numerical results are compatible with experimental performance data. It determined that RNG method in CFD analysis of radial turbo machines has provided better results than the standard k‐ε method. In addition, when using the RNG method, the phenomena of flow field were more visible than other methods.Originality/valueThis paper offers use of the RNG method as a superior turbulence method in CFD analysis of radial turbo machines.

Incomplete sensitivities for 3D radial turbomachinery blade optimization

We are interested in optimal design of 3D complex geometries, such as radial turbomachines, in large control space. The calculation of the gradient of the cost function is a key point when a gradient based method is used. Finite difference method has a complexity proportional to the size of the control space and the adjoint method requires important extra coding. We propose to consider the incomplete sensitivities method for optimal design of radial turbomachinery blades. The central point of the paper is how to adapt some formulations in radial turbomachinery to the validity domain of incomplete sensitivities. Also, we discuss on how to improve the accuracy of incomplete sensitivities using reduced order models based on physical assumptions. Fine/Turbo flow solver is coupled with gradient based optimization algorithms based on CAD-connected frameworks. Newton methods together with incomplete expressions of gradients are used. The approach is validated through optimization of centrifugal pumps. Finally the results are considered and discussed.

Design and CFD analysis of centrifugal compressor for a microgasturbine

PurposeThis paper aims to show how a good compressor can be designed and modeled with CFD steady models and to explain reasons for discrepancies between experiment (1D design) and 3D CFD analysis.Design/methodology/approachA model with only one impeller channel was used to compare 1D design data, which were obtained from centrifugal compressor design code, written and developed by the authors. The often used model for CFD analysis of turbo machinery, known as “frozen‐rotor” model, only yields satisfying results for efficiency and pressure ratio, at and near the point of best efficiency. For this case, the static pressure shows a nearly uniform circumferential distribution at the inlet of the diffuser, which numerically leads to more homogeneous flow rates through the single vane channels, and thus to a more realistic time averaged flow distribution.FindingsThe numerical results with respect to performance data showed quite good agreement with experimental data at and near the operating point of best efficiency.Originality/valueThis paper offers a combined 1D and 3D numerical approach in turbo machinery design, especially in radial compressible turbo machines design.

Potential flow in elbows

Potential flow in 2D circular-arc elbows, accelerating elbows and constant-area elbows (similar to radial turbomachine flow channels) is solved by numerical methods. For circular-arc elbows, a formula is obtained which predicts velocities at mid-turn. For other locations, it is shown that velocity distributions can be collapsed into a single non-dimensional plot; a suitable explicit empirical approximation is also presented. Guidelines are thence obtained to allow estimation of minimum acceptable upstream and downstream computational domain length, magnitude of expected velocity changes, and velocity gradients; this should be of assistance in the planning of computational solutions to similar flow situations. Solutions for accelerating elbows and constant-area elbows are also presented to illustrate foreseeable similarities and differences with circular-arc elbows.

A Three-Dimensional Turbulent Flow Analysis Method for the Rotating Channels of a Centrifugal Turbomachine

A three-dimensional turbulent flow analysis method is described based on transformations of the equations to follow an arbitrary curved passage center-line and allowing for passage area and aspect ratio variations. The numerical method is arranged to allow either parabolic or partially parabolic solution methods in the main passage direction. The method has been tested for radial turbomachine elements and comparisons are included with measured internal passage flows in a radial impeller.

A Calculation Method for Incompressible Viscous, Blade-to-Blade Flow through Radial Turbomachines with Log-Spiral Blade Surfaces

A finite difference method of blade-to-blade calculation for incompressible turbulent, viscous flow through radial turbomachines having log-spiral blades lying entirely in the r-θ plane is presented. A Newtonian stress system is incorporated into the calculation which employs a slip model for flow close to the blade surfaces. The effects of turbulence are simulated by use of an enhanced molecular viscosity. This problem is of a higher mathematical order than the usual free slip, inviscid calculation commonly applied in the design and analysis of these machines and raises interesting considerations of understanding with respect to mathematical closure and boundary conditions. Experimental results for flow through an actual machine of similar geometry to that analyzed are available and comparison of streamlines and velocity profiles are made.

A general computer solution for radial and mixed flow turbomachine performance prediction

A general one dimensional performance prediction procedure applicable to both radial inflow turbines and centrifugal compressors is presented. By separating the fundamental one dimensional gas dynamic theory from the empiricism needed to extend the one dimensional analysis to a prediction procedure for a flow which is full three-dimensional, a single equation is developed to represent the flow in all types of ducts encountered in radial turbomachines. This separation of the fundamental gas dynamics from the application of empirical parameters gives the user a clear insight into the assumptions involved, and leads to a computer procedure which is constructed of a series of subroutines representing the empiricism needed for each duct. Consequently it is a relatively simple matter for the user to modify or replace any loss correlation in light of his own experience, and therefore, develop a computer prediction procedure which closely meets his own specific requirements.

Generalization of results of experimental investigations into the load carrying capacity of wheels of radial turbomachines

Generalization of results of experimental investigations into the load carrying capacity of wheels of radial turbomachines