Sono tutti giovani, ma già vantano collaborazioni con big dell’industria quali General Electric Nuovo Pignone, Eli Lylli e Trenitalia. Hanno tenacia da vendere gli ingegneri (tra i 30 e i 37 anni) che stanno trasformando in spin-off universitario la loro “creatura” nata nel 2008, la società Ergon Research.
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Heat Transfer and Pressure Drop Measurements on Rotating Matrix Cooling Geometries for Airfoil Trailing Edges
Proceedings of ASME Turbo Expo 2015 – GT2015-42594
In the present paper the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled up matrix geometries suitable for trailing edge cooling of gas turbine airfoils are investigated.
Experimental tests were carried out under static and rotating conditions. Rotating tests were performed for two different orientations of the matrix channel with respect to the rotating plane: 0deg and 30deg. This latter configuration is representative of the exit angle of a real gas turbine blade. Test models are designed in order to replicate an internal geometry suitable for blade trailing edge cooling, with a 90deg turning flow before entering the matrix array which has an axial development.
Both the investigated geometries have a cross angle of 45deg between ribs and different values of sub-channels and rib thickness: one has four sub-channels and lower rib thickness (open area 84.5%), one has six sub-channels and higher rib thickness (open area 53.5%). Both geometries have a converging angle of 11.4deg.
Matrix models have been axially divided in 5 aluminium elements per side in order to evaluate the heat transfer coefficient in 5 different locations in the main flow direction. Metal temperature was measured with embedded thermocouples and thin-foil heaters were used to provide a constant heat flux during each test.
Heat transfer coefficients were measured applying a steady state technique based on a regional average method and varying the sub-channel Reynolds number Res from 2000 to 10000 and the sub-channel Rotation number Ros from 0 to 0.250 in order to have both Reynolds and Rotation number similitude with the real conditions.
A post-processing procedure, which takes into account the temperature gradients within the model, was developed to correctly compute average heat transfer coefficients starting from discrete temperature measurements.
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2428299
Numerical Analysis of Pressure Losses in Diffuser and Tube Steam Partition Valves
Proceedings of ASME Turbo Expo 2013 – GT2013-95527
Control valves are one of the key steam turbine components both in terms of operational safety and flexibility. It is hence fundamental to correctly predict the valve characteristics at the various working conditions to accurately estimate machine performance and control logics.
Two types of partition valves typically employed in real industrial steam turbines of different power (from 1MW to 100MW) are analysed. The first type exploits a diffuser like shape to maximize the dynamic pressure recovery before the discharge into the impulse stage. Second type, based on simple tube geometry, increases the allowable flow rate providing higher pressure losses. Geometrical dimensions has been varied to cover a wide range of configurations employed in industrial applications. Exception is made for the diffuser angle and the relative fillet radius which were fixed to guarantee product standardization among the various machine sizes.
The aerodynamic performance of the partition valves were investigated with axisymmetric inflow at various shutter positioning starting from the open valve condition where the influence of the shutter is negligible. Two different solutions of shutter were investigated to allow a characterization of regulation of the steam flow based on the valve lift. The reference conditions for the entire study is 140 bar and 540 °C which are typical working conditions for steam turbines.
Pressure losses were first modelled dividing the partition valve into singular homogeneous parts such as the intake, the straight pipe, the diffuser and the discharge, for which simple correlation were available in literature. Since the experimental data were collected for incompressible flows, the overall characteristic curve was validated using CFD computations reproducing real working conditions. The steady state RANS solver available in the commercial code CFX was used to compute the flow and thermal field exploiting the SST turbulence model. The influence of steam real gas behaviour was explored against perfect gas modelling showing low effects in terms of dimensionless parameters.
The development of the correlation permitted to rapidly cover the selected range of geometries and conditions highlighting a dimensionless parameter able to parametrize losses insensitively to the geometrical scaling.
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1776459
Numerical Characterization of Swirl Brakes for High Pressure Centrifugal Compressors
Proceedings of ASME Turbo Expo 2013 – GT2013-94075
High pressure centrifugal compressors continue to experience vibrations due to rotordynamic stability. The main cause for aero-induced exciting forces that affects the stability, is the tangential velocity component of the gas entering the many labyrinth seals throughout the machine. In order to control or limit these swirling flows, swirl brakes are generally implemented both at the impeller eye seals and at the balance piston or division wall seal of a centrifugal compressor. This paper deals with the aerodynamic characterization, by means of CFD, of such kind of devices. Several design parameters, such as teeth lean, angle of attack and pitch-to-chord ratio have been considered and also the operating conditions (pressure level and swirl at the swirl brake inlet) are accounted for. This paper aims to improve the physical understanding of the fluid flow of centrifugal compressors swirl brakes allowing an optimization of such systems.
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1776630