Laboratory of Internal Flows

Department:   Department D 1 - Fluid Dynamics
Head:   doc. Ing. Martin Luxa, Ph.D.

To be competitive, the modern power industry needs to produce machines with a high efficiency, long service life, and reliability, all of which must be fulfilled in very demanding operation. This requires involvement of state of the art research data from different areas of knowledge, such as applied mechanics and material science. An essential discipline of applied mechanics is an internal aerodynamics, which is the subject of research and testing in our lab. We mostly focus on the flow of compressible fluid through channels of complex geometries and the fluid structure interaction. Another no less important activity is a theoretical research on the flow of non-ideal fluids. The experimental facility of our lab is located in the Aerodynamic Laboratory in Nový Knín. This laboratory houses the facilities for the research of high-speed flow through turbines, compressors, ejectors, valves, and many other power industry related applications. All our research is conducted in close collaboration with the Laboratory of Computational Fluid Dynamics.

Transonic flow past Tie-Boss coupling in extremely long turbine blades

This research includes theoretical solutions, measurements, and numerical simulations of the flow in the models of the blade cascades equipped with different variants of Tie-Boss coupling. Data measured on the cascades equipped with Tie-Boss are compared with the data measured for clean cascade. Further analysis leads to optimisation of the shape of Tie-Boss to obtain lower total pressure and kinetic energy losses, which enhances the overall efficiency of a steam turbine.

Figure 1 shows the visualisation of the surface streamlines around relatively large variant of Tie-Boss. A clearly visible flow separation region is marked as (a). This separation is caused by the interaction of the exit shock-wave with the boundary layer at the junction of Tie-Boss and the adjacent blade. Such boundary layer separation is a source of energy losses. Another well observable effect of Tie-Boss is the bending of the interaction region of the exit shock-wave and the boundary layer over the blade suction side.

Zviditelnění povrchových proudnic v okolí poměrně masivní varianty tlumicí opěrky. Oblast odtržení, označená v Obrázku 1 písmenem (a), je zřetelně vidět.

Figure 1

 

Contact:

Ing. Tomáš Radnic, 266052072, radnic@it.cas.cz

Reference:

Radnic T., Hála J., Luxa M., Šimurda D., Fürst J., Hasnedl D., Kellner J.: Aerodynamic Effects of Tie-Boss in Extremely Long Turbine Blades, Journal of Engineering for Gas Turbines and Power-Transactions of the ASME, 2018, Vol. 140(11), 112604, ISSN 0742-4795.
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2681087
doi: 10.1115/1.4040093

Project: TA03020277, 2013-2016, Technological Agency of the Czech Republic

 

Three dimensional near-wall flow in the transonic turbine blade cascades

The flow through interblade channels in the vicinity of the turbine rotor hub or rotor casing is affected by the boundary layer, which is formed over these surfaces. As such boundary layer passes the interblade channel; a number of vortex structures are formed, considerably affecting aerodynamic performance of the interblade channels. A complexity of this problem require a use of all means of aerodynamic research e.g., theoretical solutions, experiments, and numerical simulations. From the obtained data and its analysis, various vortex structures can be identified together with its origin, evolution, extent, and influence on the aerodynamic performance of the particular test article. Thank to better understanding of the near-wall flow structures, the final aerodynamic design of the turbine blades can be modified to minimize adverse effects of such structures. Then, the ultimate outcome is a better overall efficiency of the turbine.

Figure 2 shows two sections through the exit flow field of the turbine blade cascade. One of them was obtained for supersonic exit velocity while the other one for subsonic. In the resulting flow fields, the vortices originating in the vicinity of the test section side walls and the associated energy losses are well observable.

 

Figure 2

 

Contact:

Ing. David Šimurda, Ph.D., 266053352, simurda@it.cas.cz

References:

Šimurda D., Fürst J., Hála J.: Near-Wall Flow in the Blade Cascades Representing Last Rotor Root Sections of Large Output Steam Turbines, J. Therm. Sci., 30, 220–230 (2021).
https://doi.org/10.1007/s11630-020-1246-x

Šimurda D., Fürst J., Luxa M.: 3D flow past transonic turbine cascade SE 1050 — Experiment and numerical simulations, J. Therm. Sci., 22, 311–319 (2013).
https://doi.org/10.1007/s11630-013-0629-7

Projects:

    • TH02020057, 2017-2020, Technological Agency of the Czech Republic
    • GAP 101/10/1329, 2010-2013, Grant Agency of the Czech Republic

 

Transonic compressor flow

Experimental research on the compressible fluid flow through axial compressors is important but very complex problem of internal aerodynamics. Experiments are complicated because the air in wind tunnel is forced to flow from the location of the lower pressure to the location of the higher pressure. Additionally, to make the transfer of the model research data to a real machine possible, numerous conditions must be fulfilled. This requires complicated regulation of the pressure at the outlet and in many cases also the boundary layer suction from the test section side-walls and from the walls of the interblade channels to prevent large flow separation, which would spoil the measured data.

Figure 3 shows an interferogram of the portion of the flow field between the transonic compressor profiles. The compression of the gas (air) in this case occurs mostly at the normal shock wave visible in the left side of the picture.
This research is conducted in cooperation with Doosan Heavy Industry & Construction Ltd., Soul, South Korea, and is also supported by Technological Agency of the Czech Republic.

Interferogram části proudového pole mezi transsonickými kompresorovými profily.

Figure 3

 

Contact:

Ing. David Šimurda, Ph.D., 266053303, simurda@it.cas.cz

Reference:

Šimurda D., Luxa M., Šafařík P.: Aerodynamic Research on the MCA-Type Compressor Blade Cascade, Proceedings of the ASME Turbo Expo 2010: Power for Land, Sea, and Air, Volume 7: Turbomachinery, Parts A, B, and C, Glasgow, UK, June 14–18, 2010, pp. 99-108, ASME.
https://doi.org/10.1115/GT2010-22153

Projects:

    • TK03030121, 2020-2024, Technological Agency of the Czech Republic
    • Comercial orders for Doosan Heavy Industry & Construction Ltd. Soul, South Korea

 

Valves

Apart from turbine and compressor blade cascade flow research, the experiments on the flow in various assemblies of regulation and fast acting control valves, which are essential components in most of the power producing machines, are carried out in our lab. Our research in this field has an impact on the efficiency of the power producing machines, their service life, reliability, and cost. Along with the measurements of losses and mass flow rates, the investigation of the flow instabilities, which are common in such assemblies and present serious risk for safe operation.

Figure 4 shows the model of one of the complex valve assemblies measured for Doosan Škoda Power, Ltd. company, Pilsen, Czech Republic. Recording V1 shows a visualisation of the surface streamlines of the longitudinal twisted vortex in the piping downstream the valve chamber of the valve from Figure 4.

Model jedné ze složitých sestav ventilů.

Figure 4

 

Video 1

 

Contact:

Ing. David Šimurda, Ph.D., 266053303, simurda@it.cas.cz

Reference:

Sláma V., Mrózek L., Rudas B., Šimurda D., Hála J., Luxa M.: Experimental and Numerical Study on Pressure Losses and Flow Fluctuations in a High-Pressure Valve Assembly of Steam Turbine Governing System, Proceedings of the ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition, Volume 9: Oil and Gas Applications; Organic Rankine Cycle Power Systems; Steam Turbine, Virtual, Online, September 21–25, 2020, V009T23A007, ASME.
https://doi.org/10.1115/GT2020-14474

Project: TN01000007, 2019-2021, Technological Agency of the Czech Republic

 

Supersonic blade profiles

Our unique experimental facility allows to measure also transonic and supersonic flow fields between thin low-cambered tip section profiles of the long rotor turbine blades. One of the research projects was devoted to investigation of supersonic flow in flat plate profiles cascade. Since these profiles are intended for use in the last stage blades of the steam turbine, they are exposed to water erosion as the steam is partially condensing in this location. For this reason, these blades get worn after some time of operation. Therefore, it is necessary to protect the leading edge of these blades using anti-erosion protection. We are involved in the project aimed to aerodynamically optimize the shape of such protection (stellite alloy cladding) and to investigate the influence of erosion on the aerodynamic performance of these profiles.

On the colour schlieren image in Figure 5, we can observe the influence of the stellite alloy cladding of the profile leading edge on the supersonic flow field in the interblade channel. Letter (A) marks the shock wave, which is generated on the interface of the cladding and the original profile surface. Through appropriate shaping, the flow separation, negatively affecting energy losses and forces acting on the airfoil, can be prevented.

Vliv zesílení náběžné hrany profilu stelitovým návarem na supersonické proudové pole v mezilopatkovém kanálu.

Figure 5

 

Contact:

doc. Ing. Martin Luxa, Ph.D., 266053352, luxa@it.cas.cz

References:

Fořt J., Fürst J., Halama J., Hric V., Louda P., Luxa M., Šimurda D.: Numerical simulation of flow through cascade in wind tunnel test section and stand-alone configurations, Applied Mathematics and Computation, Vol. 319, February (2018), s. 633-646. ISSN 0096-3003
https://www.sciencedirect.com/science/article/pii/S0096300317305015

Luxa M., Příhoda J., Šimurda D., Straka P., Synáč J.: Investigation of the Compressible Flow through the Tip-Section Turbine Blade Cascade with Supersonic Inlet, Journal of Thermal Science, Vol. 25, č. 2 (2016), s. 138-144, ISSN 1003-2169
http://hdl.handle.net/11104/0259005

Project:

TH02020057, 2017-2020, Technological Agency of the Czech Republic

 

Flow in narrow channels

The turbulence transition in pipe and channel flow represents up to now an important topic, since it is the nature of the flow, which substantially affects the friction and associated losses. With increasing miniaturization and more detailed numerical simulations of the various small flow parts of the turbomachines, the need for experimental data to explore the physical phenomena of the narrow channel flow and to validate numerical codes is still present.

The flow in narrow channels of the rectangular cross-section of the high aspect ratio is investigated in our laboratory using the experiments and numerical simulations. Experimental investigation is carried out using various independent methods including optical and pneumatic measurements and hot-film anemometry. The topics of investigation include the influence of the oriented surface roughness on the flow development and the wall shear stress and investigation of the phenomena of the aerodynamic choking due to friction.

Figure 6 pictures the comparison of the computed lines of constant density (upper half) with the measured interference fringes (also lines of constant density) in the exit region of the narrow channel during the air expansion to very low pressure. Despite the apparent similarity of the measured and computed flow fields, the values of the wall shear stress measured using the hot-film probe significantly differs in some of the measured regimes from those computed using the commercial CFD code. Therefore, to correctly predict the wall shear stress, the numerical model need to be modified for this specific purpose and validated.

Porovnání vypočtených čar konstantní hustoty (horní polovina) s naměřenými interferenčními proužky.

Figure 6

 

Contact:

Ing. Jindřich Hála, 266053303, hala@it.cas.cz

References:

Prausová H., Bublík O., Vimmr J., Hála J., Luxa M.: Numerical and Experimental Investigation of Compressible Viscous Fluid Flow in Minichannels, Proceedings of Computational mechanics 2019, Pilsen: University of West Bohemia, 2019, (Adámek V., Jonášová A., Plánička S., Zajíček M.), 160-163, ISBN 978-80-261-0889-4.

Hála J., Luxa M., Bublík O., Prausová H., Vimmr J.: Clearance gap flow: Extended pneumatic measurements and simulations by discontinuous Galerkin finite element method, EPJ Web of Conferences. - (Doro, M.), Vol. 114, March (2016), 02034-02034, ISSN 2101-6275.

Hála J., Luxa M., Bublík O., Prausová H., Vimmr J.: Clearance gap flow: Simulations by discontinuous Galerkin method and experiments, EPJ Web of Conferences, Vol. 92, May (2015), 02073-02073, ISSN 2100-014X.

Project: GAČR No. 101/08/0623, Grant Agency of the Czech Republic

Mach-Zehnder interferometer

A unique apparatus used for flow field visualisation of compressible fluids. Obtained images depicting fields of interference fringes can be evaluated to obtain, for instance, pressure distribution over the tested profile. The apparatus used in our lab was manufactured by Novotechnik company in Stuttgart and in our lab has been used since 1965. It has a unique large field of view of approximately 160 mm in diameter.

Machův-Zehnderův interferometr Figure 7a

Machův-Zehnderův interferometr Figure 7b

 

Traversing device

Air flow properties including its kinetic energy can be determined using pneumatic probe measurements. The most common probe used in our lab is the five-hole conical probe, which is capable to measure the static pressure, total pressure, and flow direction. From these properties together with the flow parameters at the inlet to the measurement section, one can determine the loss of kinetic energy due to irreversible processes occurring during the flow past a tested article. The pneumatic probe is a part of traversing device, which enables the automatic positioning of the probe in examined flow field. It allows translation in two axes and rotation in the plane of the flow. The rotation to flow direction can be carried out real-time using a PID regulator.

Figure 8 shows a 3D model of the traversing device with the conical five-hole pneumatic probe.

 

Figure 8

 

Pressure and temperature sensitive paints

Pressure distribution over the surfaces of the articles being tested can be examined using the pressure sensitive paints. These paints fluoresce under the UV light in differing intensities depending on the surrounding oxygen concentration. Temperature sensitive paints are capable to locate transition to turbulence since the turbulent flow exhibits higher wall shear stress (more intensive mixing), therefore, higher heat exchange. Both mentioned methods are limited by the necessity of the optical access to light the examined surface and at the same time capture the images with a high-speed camera. Our laboratory is equipped with the state of the art facility, which is promising for overcoming of the mentioned drawback.

Figure 9 pictures the pressure distribution over a wedge in the supersonic flow. These results were obtained in NASA LRC.

Figure 9

Lepicovsky, J. - Bencic, TJ. - Bruckner, R.J.: Application of Pressure Sensitive Paint to Confined Flow at Mach Number 2.5. NASA Report NASA/TM-1998-107527

 

Hot-film anemometry

is a method for boundary layer investigation, which is based upon the similarity between the velocity profile in the vicinity of a body submerged in the flow and the temperature profile generated by a heated element located at the surface of the body. Hot-film probes are usually available in two variants. The first one is the probe with one hot-film sensor, such as Dantec 55R45. This probe is intended for repeated use and the calibration to obtain the wall shear stress is possible. The second version is an array of hot films deposited using an electron beam on a thin adhesive foil. Despite that such design is suitable rather for qualitative measurements, the data obtained using the array of hot films might provide valuable data on the location of the laminar-turbulent transition.

Figure 10 shows the hot-film array at the suction side of the profile being examined, which is intended for the tip section of the long blade of the high output steam turbine. Measured data can provide information about the boundary layer character and laminar-turbulent transition.

Figure 10

 

Transonic calibration facility for multi-hole pressure probes

A number of pressure probes utilised in our lab for measurement of the static and total pressure as well as the flow angle require calibration. During the calibration, the probe is placed in a flow of known parameters and the probe data are read. If this is done for several flow regimes, the calibration dependence can be obtained. For this purpose, our lab is equipped with the calibration facility, which enables to set desired flow parameters and at the same time automatically move the probe to obtain its directional calibration. The facility is equipped with a nozzle, which allows the calibration up to approximately Mach number M=1.3.

Figure 11 shows the nozzle outlet of the calibration facility with a five-hole conical probe being calibrated.

Figure 11

Offered topics:
Experimental investigation of forces in blade cascades
Blade cascade in supersonic flow field
Interferometric measurements of flow field in surroundings of oscillating body and their processing

Ongoing topics:
Compressible fluid flow through narrow channels (Jindřich Hála)
Force effects and irreversible phenomena during the flow past the model of the middle section of the large output steam turbine rotor blade equipped with Tie-Boss damping device (Tomáš Radnic)

Completed topics:
High-Speed Flow past a Radial Stator Turbine Cascade (Martin Luxa, 2005)
Transonic and Supersonic Flow Past Turbine Profile Cascades (David Šimurda, 2011)