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This paper investigates the flow past two variants of root section profile cascades for a last stage rotor considering three-dimensional flow structures in the near-wall region. Analyses were drawn based on RANS numerical simulations of both variants and on the experimental data obtained by the 3D traversing in the exit flow field of one of the variants. Extent of 3D structures at two different regimes and its influence on aerodynamic characteristics of the blade cascades was assessed. The distributions of Mach number along the profiles were compared with 2D optical measurements and its distortion due to the presence of the sidewall was explored. The interaction between main vortical structures was described and its influence on the loading of the blades, mechanical energy losses and exit flow angle was discussed. The results showed that for a front loaded blade the vortical structures appeared earlier and at a larger extent than for an aft loaded variant. However, due to different Mach number distribution, contribution of end wall flow to the energy losses was lower in the case of the aft loaded variant. The influence of the near wall flow on the loading was found to be rather weak while the deviation of the exit flow angle appeared to be comparable for both of the variants.

The paper deals with selected phenomena present in a blade cascade flow field. The presented research was performed on prismatic blade cascades composed mostly of the tip and root sections of the last stage rotor blade of a large output steam turbine. The unstarted supersonic flow on the cascade inlet, the separation of the flow and the swirl line behind the trailing edge have been identified as the possible sources of the unsteady force effects.

The paper is concerned with numerical investigation of 3-D flow field in a last stage rotor blading in a steam turbine of large power output. The mid-span section of 1220 mm long blade is equipped with a stabilization device called tie-boss, two variants of which have been investigated. The tie-boss presents considerable disruption to the flow field and is a reason of loss of efficiency and origin of vortices. The investigation has been conducted in Ansys CFX. Detailed investigation determined origins of vorticial structures and identified separations, which have non-negligible effect on the aerodynamic parameters of the blade cascade. The research allows comparison of the quality of the flow field of both tie-boss variants. The results show that the tie-boss with round trailing edge causes lower loss coefficient increase and higher exit flow angle change than the variant with tailored trailing edge.

Blade flutter problems will become more serious in the near future for large power generating turbines as unavoidable consequences of the increasing share of power generated by renewable energy sources. The Institute of Thermomechanics of the Czech Academy of Sciences (IT CAS) was awarded a grant to initiate a blade flutter research program. The main thrust of the IT CAS role in this program is to pursue advancements in experimental technique applications and to establish a reliable experimental database of blade mutual aerodynamic interactions during the blade flutter onset for the sonic and transonic flow regimes in particular. A new sophisticated test section for transonic blade flutter research was designed and being manufactured to fulfill such requirements. Experience gained while working with the NASA Transonic Flutter Cascade facility resulted in new innovative features included in the new design. The new facility will be delivered to the High-Speed Laboratory in Novy Knin by the end of September 2020.

This study presents the comparison of aerodynamic performances of two successive designs of the root profiles for the ultra-long rotor blade equipped with a straight fir-tree dovetail. Since aerodynamic and strength requirements laid upon the root section design are contradictory, it is necessary to aerodynamically optimize the design within the limits given by the foremost strength requirements. The most limiting criterion of the static strength is the size of the blade cross-section, which is determined by the number of blades in a rotor and also by the shape and size of a blade dovetail. The aerodynamic design requires mainly the zero incidence angle at the inlet of a profile and in the ideal case ensures that the load does not exceed a limit load condition. Moreover, the typical root profile cascades are transonic with supersonic exit Mach number, therefore, the shape of a suction side and a trailing edge has to respect transonic expansion of a working gas. In this paper, the two variants of root section profile cascades are compared and the aerodynamic qualities of both variants are verified using CFD simulation and two mutually independent experimental methods of measurements (optical and pneumatic).

This article is concerned with the new design of supersonic profile cascade, marked TR-U-8, for ultra-long bucket tip area. The profile cascade represents a geometrical variant of the ultra-long bucket tip section which was designed in Doosan Skoda Power in Pilsen. There were found out outputs of two aerodynamic regimes marked OP1 India 800 MW for higher back-pressure and OP4 Temelin 1200 MW for lower back pressure. Outputs for nominal incidence cascade angle are presented in this paper. The design of cascades by aerodynamic calculations were investigated and validation by evaluation of optical and pneumatic measurements on wind tunnel tests was done. Two dimensional cascade calculations were carried out by commercial code Ansys Fluent 16.0 in Doosan Skoda Power (DSPW) and by non-commercial software developed in Czech Technical University (CTU). An aerodynamic high speed wind tunnel is located in Institute of Thermomechanics the Czech Academy of Science (AS CR).

Focus of this paper is aerodynamic investigation of tie-boss stabilization devices for extremely long rotor blades. This investigation covered measurements on multiple blade cascades and computational fluid dynamics (CFD) simulation of the flow past these cascades. Conclusions were drawn from results of the measurements and CFD and from the knowledge of prior investigation of the used blade cascade. Main focus of this paper is to describe influence of a tie-boss stabilization device on flow field in interblade channel. Tie-boss with more massive shape proved to cause lesser losses, while tie-boss with a tailored trailing edge showed lesser influence on flow turning.

In the present paper, new results of measurements of the compressible viscous fluid flow in narrow channels with parallel walls under the conditions of aerodynamic choking are presented. Investigation was carried out using the improved test section with enhanced capability to accurately set the parallelism of the channel walls. The measurements were performed for the channels of the dimensions: length 100 mm, width 100 mm and for various heights in the range from 0.5 mm to 4 mm. The results in the form of distribution of the static pressure along the channel axis including the detailed study of the influence of the deviation from parallelism of the channel walls are compared with previous measurements and with numerical simulations performed using an in-house code based on Favre averaged system of Navier-Stokes equations completed with turbulence model of Spalart and Allmaras and a modification of production term according to Langtry and Sjolander. The spatial discretization of the governing equations is performed using the discontinuous Galerkin finite element method which ensures high order spatial accuracy of the numerical solution.

The aerodynamics of root sections appears to be a crucial problem in the design and operation of the last stages of large output steam turbines. The reasons are transonic flow, high flow turning, and difficulties with keeping their design aerodynamic conditions during operation. Investigations were performed on planar blade cascades representing root sections of 1085mm and 1220mm long rotor blades. The basic conception of the two root sections differs. The aerodynamic loading of the 1220mm blade root section is lowered in order to ensure that the design parameters are kept during turbine stage operation. We present the results of optical and pneumatic measurements i.e. dependencies of the kinetic energy loss coefficient and exit flow angle on the exit isoentropic Mach number and the angle of incidence, as well as images of the flow fields. The experimental data is analyzed in order to assess and document the difference between the two root section designs.

This paper presents the experimental results of aerodynamic research performed on a blade cascade representing the midsection of 1220 mm long rotor blades of the last stage of a large output steam turbine. The operational regime of the blade cascade is characterized by supersonic exit velocity. Isentropic exit Mach number M2is = 1.323. The experimental data analysis concerns pneumatic measurements to calculate the total pressure and the kinetic energy loss coefficients, and to evaluate them mainly with respect to the aperiodicity of the flow field. The flow structure is also studied on the basis of results obtained by means of optical methods, such as schlieren and interferometric methods.Copyright © 2010 by ASME

This paper deals with an analysis of the flow through a high cambered compressor blade cascade. The profiles of the blade cascade have been designed to be of MCA-type. The geometric and aerodynamic parameters of the cascade are presented here. The aerodynamic research was performed in a transonic wind tunnel. Optical methods were applied to obtain information on the flow structures taking place in the interblade channels when operating in a range of subsonic and transonic velocities and at various angles of incidence. The internal shock waves and the flow separation in the rear part of the cascade channel were observed and studied. Their influence on the loss coefficient and exit flow angle at subsonic and low transonic region was assessed. The thickness of the sidewall boundary layer in the interblade channel was measured in order to investigate the development of the axial velocity density ratio (AVDR), which plays an important role in the interpretation of the results.Copyright © 2010 by ASME

This paper reports on the results of high-speed aerodynamic research on a blade cascade. The blade cascade represents the tip section of the last stage rotor blades of a large output steam turbine. The aerodynamic characteristics of the blade cascade are presented together with flow field photographs in a range of transonic and supersonic velocities. Pictures of the flow field were obtained by means of interferometry and the schlieren method. The pressure distribution over the profiles was also evaluated using interferometry. Finally, the data for evaluating the losses and other integral characteristics of the flow exiting from the cascade were measured pneumatically with the use of a traversing device. The results are analyzed and discussed.

The paper presents results from an aerodynamic investigation of transonic flow past profile cascades. The analysis following the experimental data is aimed at transonic effects namely expansion over sonic conditions, aerodynamic choking, supersonic compression accompanying transonic expansion on the suction side, boundary layer development, the flow past a trailing edge, exit shock waves, interaction of shock wave with boundary layer, wakes, etc.

Aerodynamic investigations were performed on planar blade cascades representing two alternative root sections of rotor blades 54″ in length with straight fir-tree root. Each of the variants was designed for different number of blades in the rotor. This paper presents the results of measurements showing the dependency of the kinetic energy loss coefficient and the exit flow angle on the exit isoentropic Mach number and the angle of incidence. Images of the flow fields are also presented. The experimental data is analyzed to assess and document the difference between the two root section designs. Results show that requirement of straight fir tree root leading to high design incidence angles significantly limit operation range. Also in case of root sections with high exit Mach numbers a limit load conditions are an issue. In order to utilize available pressure drop blade cascade throat/pitch ratios should be kept as high as possible which favorites variant with lower number of blades and higher outlet metal angle (relative to axial direction).