Dynamics of Forced and Self-Excited Instabilities in Heterogeneously/Homogeneously Condensing Flows through Nozzles and Steam Turbine Cascades

Recent trends in the electric energy market such as biomass, waste incineration or combined cycle power plants require innovative solutions in steam turbine design. Variable operating conditions cause significant changes in flow field surrounding the steam turbine last stage blades. Therefore, the enlargement of operating range for last stage blades presents new challenges in design of turbine cascades. Several turbine cascades were designed and analyzed by commercial and in-house software of CTU Prague. Selected profiles were experimentally validated in the high-speed wind tunnel for 2D cascade measurements of the Institute of Thermomechanics of the Czech Academy of Sciences which is equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard. Comparisons are presented of numerical results with optical and pneumatic measurements for a wide range of inlet and outlet Mach numbers for optimized hub and tip profile cascades.

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Numerical Simulations of Unsteady Wet Steam Flows With Non-Equilibrium Condensation in the Nozzle and the Steam Turbine

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2006-98202 ◽

2006 ◽

Cited By ~ 10

Author(s):

Shigeki Senoo ◽

Alexander J. White

Keyword(s):

Heat Release ◽

Steam Turbine ◽

Laval Nozzle ◽

Expansion Rate ◽

Droplet Growth ◽

Layer Model ◽

Pressure Distributions ◽

Condensing Flows ◽

Two Layer Model ◽

Non Equilibrium

Numerical techniques for non-equilibrium condensing flows are presented. Conservation equations for homogeneous gas-liquid two-phase compressible flows are solved by using a finite volume method based on an approximate Riemann solver. The phase change consists of the homogeneous nucleation and growth of existing droplets. Nucleation is computed with the classical Volmer-Frenkel model, corrected for the influence of the droplet temperature being higher than the steam temperature due to latent heat release. For droplet growth, two types of heat transfer model between droplets and the surrounding steam are used: a free molecular flow model and a semi-empirical two-layer model which is deemed to be valid over a wide range of Knudsen number. The computed pressure distribution and Sauter mean droplet diameters in a convergent-divergent (Laval) nozzle are compared with experimental data. Both droplet growth models capture qualitatively the pressure increases due to sudden heat release by the non-equilibrium condensation. However the agreement between computed and experimental pressure distributions is better for the two-layer model. The droplet diameter calculated by this model also agrees well with the experimental value, whereas that predicted by the free molecular model is too small. Condensing flows in a steam turbine cascade are calculated at different Mach numbers and inlet superheat conditions and are compared with experiments. Static pressure traverses downstream from the blade and pressure distributions on the blade surface agree well with experimental results in all cases. Once again, droplet diameters computed with the two-layer model give best agreement with the experiments. Droplet sizes are found to vary across the blade pitch due to the significant variation in expansion rate. Flow patterns including oblique shock waves and condensation-induced pressure increases are also presented and are similar to those shown in the experimental Schlieren photographs. Finally, calculations are presented for periodically unsteady condensing flows in a low expansion rate, convergent-divergent (Laval) nozzle. Depending on the inlet stagnation subcooling, two types of self-excited oscillations appear: a symmetric mode at lower inlet subcooling and an asymmetric mode at higher subcooling. Plots of oscillation frequency versus inlet sub-cooling exhibit a hysteresis loop, in accord with observations made by other researchers for moist air flow.

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Application of Artificial Neural Networks in Investigations of Steam Turbine Cascades

Journal of Turbomachinery ◽

10.1115/1.3103923 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 4

Author(s):

Krzysztof Kosowski ◽

Karol Tucki ◽

Adrian Kosowski

Keyword(s):

Neural Networks ◽

Artificial Neural Networks ◽

Steam Turbine ◽

High Performance ◽

Cross Sectional ◽

Complementary Method ◽

Numerical Tests ◽

Flow Parameters ◽

Turbine Cascades ◽

Artificial Neural

We present the results of numerical tests of artificial neural networks (ANNs) applied in the investigations of flows in steam turbine cascades. Typical constant cross-sectional blades, as well as high-performance blades, were both considered. The obtained results indicate that ANNs may be used for estimating the spatial distribution of flow parameters, such as enthalpy, entropy, pressure, velocity, and energy losses, in the flow channel. Finally, we remark on the application of ANNs in the design process of turbine flow parts, as an extremely fast complementary method for many 3D computational fluid dynamics calculations. By using ANNs combined with evolutionary algorithms, it is possible to reduce by several orders of magnitude the time of design optimization for cascades, stages, and groups of stages.

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Comparative Experimental Investigation on Aerodynamic Performance of a Steam Turbine Cascades: Part II — Stator Vanes

Volume 5B: Oil and Gas Applications; Steam Turbines ◽

10.1115/gt2013-94815 ◽

2013 ◽

Author(s):

Lei Gao ◽

Qun Zheng ◽

Hang Chen

Keyword(s):

Pressure Gradient ◽

Steam Turbine ◽

Aerodynamic Performance ◽

Wake Region ◽

Uniform Loading ◽

Experimental Conditions ◽

Blade Height ◽

Comparative Experimental Investigation ◽

Turbine Cascades ◽

Loading Type

In this paper, the eighth and the ninth stage stator blades of a marine steam turbine are improved and the experimental research has been carried out on aerodynamic performance at 50% blade height of the original and the improved plane cascades. The experimental results indicate that both of the two original stator blades are uniform loading type, which are improved and designed as the aft-loaded. The results also show that, comparing with the original blade, the improved one can shorten the length of reverse pressure gradient, therefore the reverse pressure gradient is reduced and the adaptability of cascades to incidence variation is enhanced. Meanwhile, the thin trailing edge of aft-loaded blade not only increases the base pressure of the wake region, but also reduces the width of the wake region. In addition, the results reveal that the losses of modified blades are lower than the original ones under the experimental conditions of different exit Mach numbers and different angle of incidences.

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Loss generation in radial outflow steam turbine cascades

10.29008/etc2017-039 ◽

2017 ◽

Cited By ~ 1

Author(s):

Aki Grönman ◽

Antti Uusitalo ◽

Jari Backman

Keyword(s):

Steam Turbine ◽

Turbine Cascades ◽

Radial Outflow

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Comparative Experimental Investigation on Aerodynamic Performance of Steam Turbine Cascades: Part I — Rotor Blades

Volume 5B: Oil and Gas Applications; Steam Turbines ◽

10.1115/gt2013-94814 ◽

2013 ◽

Author(s):

Lei Gao ◽

Qun Zheng ◽

Hang Chen

Keyword(s):

Steam Turbine ◽

Large Degree ◽

Aerodynamic Performance ◽

Rotor Blades ◽

Aerodynamic Loss ◽

Transverse Pressure ◽

Comparative Experimental Investigation ◽

Last Stage ◽

Turbine Cascades ◽

End Wall

In this paper, the static aerodynamic performance of the second to last stage rotor blades of a marine steam turbine is experimentally investigated. The experiments have been carried out for both original blade (ORI R1) and modified blade (MOD R1) annular cascades. The experimental results indicate that the straight original blade is aft-loaded type, and there is a large degree of diffusion at the tip end wall. The improvement methods include adopting twist blades, adjusting the blade profile to reach the aft-loaded as much as possible at both end walls as well as combining with the cylindrical meridian lines. It has been found in the experiment that the transverse pressure gradient of the modified decreases at both end walls, so does the loss of the flow, especially it weakens the secondary flow at the tip end wall. The aerodynamic loss coefficient of improved blades has reduced by about 25%.

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A Discrete Adjoint Method for Two-Phase Condensing Flows Applied to the Shape Optimization of Turbine Cascades

Journal of Turbomachinery ◽

10.1115/1.4047781 ◽

2020 ◽

Vol 142 (11) ◽

Author(s):

M. Pini ◽

L. Azzini ◽

S. Vitale ◽

P. Colonna

Keyword(s):

Shape Optimization ◽

Adjoint Method ◽

Volume Fraction ◽

Liquid Volume ◽

Two Phase ◽

Discrete Adjoint ◽

First Case ◽

Discrete Adjoint Method ◽

Condensing Flows ◽

Turbine Cascades

Abstract This paper presents a fully turbulent two-phase discrete adjoint method for metastable condensing flows targeted to turbomachinery applications. The method is based on a duality preserving algorithm and implemented in the open-source CFD tool SU2. The optimization framework is applied to the shape optimization of two canonical steam turbine cascades, commonly referred to as White cascade and Dykas cascade. The optimization were carried out by minimizing either the liquid volume fraction downstream of the cascade or the total entropy generation due viscous effects and heat transfer. In the first case, the amount of condensate turned out to be reduced by as much as 24%, but without reduction of the generated entropy, while the opposite resulted in the second case. The outcomes demonstrate the capability and computational efficiency of adjoint-based automated design for the shape optimization of turbomachinery operating with phase change flow.

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