Experimental study of the effects of temperature variation on droplet size and wetness fraction in a low-pressure model steam turbine

Eberle, T.; Schatz, Markus; Starzmann, Jörg; Grübel, Marius; Casey, Michael

doi:10.1177/0957650913508119

Cited by 9 publications

(14 citation statements)

References 8 publications

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“…Comparisons between numerical predictions and measured data for model or full-size turbines have been presented for a limited number of operating conditions [4,[6][7][8]. Of particular relevance to this work is the study performed by Eberle et al [9] that compared experimental and numerical results for different inlet Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project.…”

Section: Introductionmentioning

confidence: 99%

A Study of Spontaneous Condensation in an LP Test Turbine

Chandler

Melas

Jorge

2015

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines

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Recent advances in computational fluid dynamics (CFD) offer the possibility to predict condensing flows in 3D LP steam turbine geometries. Correct analysis of wetness losses, droplet deposition and other two-phase effects in LP steam turbines requires accurate prediction of the non-equilibrium flow field and droplet sizes.The paper compares numerical results from a 3D, polydispersed, condensing flow CFD code to experimental data measured in a scaled model LP turbine for a range of operating conditions. In order to compare the computed efficiencies with the measured values, a method for averaging non-equilibrium flow fields has been developed. Comparisons are made between computational and experimental results for a series of inlet temperature variation tests where the inlet and exit pressures were kept constant. The steady calculations accurately predict the temperature that the primary nucleation zone moves to an upstream row. Furthermore, the mechanism of condensation as nucleation changes rows is explored and it is shown that initially a significant degree of subcooling is maintained in the inter-blade section and, as a result, nucleation occurs at a relatively low rate in a zone that extends far downstream of the blade's trailing edge. This produces relatively large droplets compared to when nucleation occurs predominantly within the blade passage and is clearly visible in the measured module efficiencies and local flow angles, static pressures and light extinction. The measured variation of efficiency and specific work with inlet temperature is predicted accurately by the computations.It is concluded that steady condensing flow wet-steam * Address all correspondence to this author.calculations are able to predict the location of nucleation and the variation of flow dynamics and performance with inlet temperature accurately. A description of the condensation process as nucleation moves between rows has been given and is consistent with the numerical and experimental results.

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Section: Introductionmentioning

confidence: 99%

A Study of Spontaneous Condensation in an LP Test Turbine

Chandler

Melas

Jorge

2015

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines

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“…Schatz and Eberle [2] published wetness mea surement results obtained in the model steam turbine test rig and pointed out that there are discrepancies to CFD results regarding the local wetness as well as the droplet diameter and number. The influence of the turbine inlet temperature on the position of nucleation has been confirmed in measurements and numerical simula tions by Eberle et al [3]. But again, the agreement between experiment and CFD was not satisfying.…”

Section: Introductionmentioning

confidence: 74%

Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines—Part I: Numerical Validation of Wet Steam Models and Turbine Modeling

Grübel

Starzmann

Schatz

et al. 2014

Journal of Engineering for Gas Turbines and Power

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In this publication, an overview of the current state of wetness modeling at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) is given. For the model ing, an Euler-Euler method implemented in the commercial flow solver ansys CFX is used. This method is able to take into account the nonequilibrium state of the steam and models the interactions between the gaseous and liquid phases. This paper is the first part of a two-part publication and deals with the numerical validation of wet steam mod els by means of condensing nozzle and cascade flows. A number of issues with regard to the quality of the computational fluid dynamics (CFD) code and the applied condensation models are addressed comparing the results to measurements. It can be concluded that a calibration of the models is necessary to achieve a satisfying agreement with the experi mental results. Moreover, the modeling of the low pressure model steam turbine operated at the ITSM is described focusing on the asymmetric flow field in the last stage caused by the axial-radial diffuser. Different simplified axisymmetric diffuser models are investi gated in steady state simulations, and the results and the arising issues for part-load, design-load, and over-load conditions are discussed. Thereafter, a comparison between the equilibrium and nonequilibrium steam modeling approaches is performed and the advantage of the nonequilibrium model is highlighted. The second part of the publi cation focuses on experimental investigations and compares the numerical results to wetness measurement data. For this purpose, different loads are also considered.

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“…The appearance of larger droplets has been discussed by Eberle et al [11] and explained with a possible unsteadiness in the local subcooling, being partly high enough at the stator exit to allow the formation of a few larger droplets at the stator outlet and in the axial gap. Because these few droplets do not allow sufficient con densation, steam subcooling prevails and leads to a formation of small droplets in the next blade row.…”

Section: Refl [Id-mentioning

confidence: 92%

Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines—Part II: Turbine Wetness Measurement and Comparison to Computational Fluid Dynamics-Predictions

Schatz

Eberle

Grübel

et al. 2014

Journal of Engineering for Gas Turbines and Power

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T w o -P h a s e F lo w M o d e lin g andM e a s u re m e n ts in L o w -P re s s u re T u rb in e s -P art II: T u rb in e W e tn e s s M e a s u re m e n t and C o m p ariso n to C o m p u ta tio n a l F luid D y n a m ic s -P re d ic tio n s The correct computation o f steam subcooling, subsequent formation o f nuclei and finally droplet growth is the basic prerequisite fo r a quantitative assessment o f the wetness losses incurred in steam turbines due to thermal and inertial relaxation. The same basi cally applies fo r the prediction o f droplet deposition and the resulting threat o f erosion. Despite the fa ct that there are many computational fluid dynamics (CFD)-packages that can deal with real-gas effects in steam flows, the accurate and reliable prediction o f sub cooling, condensation, and wet steam flow in steam turbines using CFD is still a demand ing task. One reason fo r this is the lack o f validation data fo r turbines that can be used to assess the physical models applied. Experimental data from nozzle and cascade tests can be found in the open literature; however, these measurement results are only partly useful fo r validation purposes fo r a number o f reasons. With regard to steam turbine test data, there are some publications, yet always without any information about the turbine stage geometries. This publication is part o f a two-part paper; whereas Part I focuses on the numerical validation o f wet steam models by means o f condensing nozzle and cascade flows, the focus in this part lies on the comparison o f CFD results o f the turbine flow to experimental data at various load conditions. In order to assess the validity and reliability o f the experimental data, the method o f measurement is presented in detail and dis cussed. The comparison o f experimental and numerical results is used fo r a discussion about the challenges in both modeling and measuring steam turbine flows, presenting the current experience and knowledge at Institute o f Thermal Turbomachinery and Machin ery Laboratory (ITSM).

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Experimental study of the effects of temperature variation on droplet size and wetness fraction in a low-pressure model steam turbine

Cited by 9 publications

References 8 publications

A Study of Spontaneous Condensation in an LP Test Turbine

A Study of Spontaneous Condensation in an LP Test Turbine

Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines—Part I: Numerical Validation of Wet Steam Models and Turbine Modeling

Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines—Part II: Turbine Wetness Measurement and Comparison to Computational Fluid Dynamics-Predictions

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