Martin Luxa

Loss Coefficient Dependence of Turbine Blade Cascade

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

Investigation of transonic and supersonic flow in the rotor tip section of the last LP steam turbine stage under different turbulence levels.

Design of a new generation of the large power steam turbines leads to very long last rotor blades with tip sections operating often in supersonic region. The flow field in such tip sections is not fully explored and it is believed to be fairly complex and very sensitive even on minute changes of flow parameters. This stimulated the study of the performance of profiles suitable for rotor tip sections. Numerical simulations have been carried out using TU Prague’s code based on the solution of the RANS equations and SST turbulence model by implicit finite volume method with AUSMPW+ scheme in high resolution formulation. Experimental data have been gathered in the intermittent high-speed wind tunnel of IT CAS CR for 2D cascade measurements equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard.

Wind Tunnel Measurements of Flow-Induced Vibration of a NACA0015 Airfoil Model

The paper reports on interferometric measurements of flow over a NACA0015 airfoil model during flutter limit cycle oscillations. The airfoil model is fixed on an elastic support allowing motion with two degrees of freedom — pitch and plunge. The structural mass and stiffness matrices can be tuned to certain extent, so that the eigenfrequencies of the two modes approach as needed. The model is equipped with dynamic pressure probes and sensors measuring the airfoil vertical position. The flow field around the airfoil was measured by Mach-Zehnder interferometer and registered using a high-speed camera synchronously with the mechanical vibration and pressure measurements. The Mach number of the incident airflow was gradually increased and the response of the aeroelastic system to initial impulse measured, until the flutter instability onset occurred. Flutter boundaries were evaluated for various additional masses attached (i.e., for various plunging mode eigenfrequencies), and post-critical behavior of the system investigated. The interferograms recorded by the high-speed camera were postprocessed, yielding pressure distribution around the airfoil during its vibration and an estimate of the total aerodynamic force and energy transfer from the airflow to the structure.Copyright

Aerodynamic Investigations of Root Sections of Long Rotor Blades Applied at the Last Stages of Steam Turbines

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.Copyright

Aerodynamic Research on the MCA–Type Compressor Blade Cascade

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

Research on the Tip Sections of a Long Turbine Blade

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.© 2008 ASME

Transonic Flow Past Plane Cascades: Experimental Data Analysis

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.