Alessandro Salvagni

Unsteady CFD Analysis of Erosion Mechanism in the Coolant Channels of a Rotating Gas Turbine Blade

The two-phase flow in a rotating wedge mimicking the final portion of a blade turbine internal cooling channel is here presented and discussed focusing on unsteady motion and erosion mechanisms. The rotation axis is placed to properly reproduce a configuration with a very strong deviation (90°).The flow field was modelled by using the well known k-e-ζ-f unsteady-RANS model based on the elliptic-relaxation concept. The model was modified by some of the authors to take into account the influence of turbulence anisotropy as well as rotation. The model was applied to the well-established and fully validated T-FlowS code.A systematic comparison of rotating and non-rotating case was carried out to show the influence of Coriolis force on flow and erosion mechanisms.The rotational effects strongly changed the flow behaviour within the channel, affecting both the unsteady flow and the particles trajectories. In the rotating case, there is no recirculation on the tip region; besides, position of the small recirculation regions above each pedestals change. These, and other minor effects, affect the particle motion thus resulting in a different erosion pattern.Copyright

Study of Particles Deposition in Gas Turbine Blades in Presence of Film Cooling

Exhaust entering the gas turbine is usually fed with solid particles produced in the combustion of hydrocarbons (ashes, unburned char, etc.). Then, the interaction between the particles motion and the film cooling jets must be properly addressed.Here an integrated approach based on an Eulerian-Lagrangian scheme for particle-laden flow was applied to a real turbomachinery case. The code was preliminary assessed by simulating two simplified test cases: a) 3-D cooling jet in a channel; b) 2-D turbine cascade with film cooling. These cases were selected to separately validate the main effects here considered: a) interaction of particles trajectories and 3D cooling jets; b) effect of the cooling jets on surface temperature and particles trajectory and possibly on particle deposition, in comparison with the non-cooled case.Finally, 3D simulation of the particle-laden flow around a real E3 gas turbine vane with and without film cooling was performed. Flow features, particles trajectories and deposit on the blade are presented.The compressible flow field was simulated using the OpenFOAM code obtaining credible predictions of the velocity and temperature field.Then the P-Track code developed by the authors was applied for tracking the particles trajectories and determining the deposit on the solid surface. As the temperature are relatively high, the sticking probability method, that is strongly dependent on the temperature itself, was used here.The results showed that the presence of the cooling jets affect deeply the deposit following two main causes: the influence of the jets in removing the fluid from the close-to-the-wall region and the reduction of temperature along the blade.Copyright

Effects of Wall Curvature on the Dynamics of an Impinging Jet and Resulting Heat Transfer

The effects of wall curvature on the dynamics of a round subsonic jet impinging on a concave surface are investigated for the first time by direct numerical solution of the compressible Navier-Stokes equations. Impinging jets on curved surfaces are of interest in several applications, such as the impingement cooling of gas turbine blades. The simulation is performed at Reynolds and Mach numbers respectively equal to 3, 300 and 0.8. The impingement wall is kept at a constant temperature, \(80\,\text {K}\) higher than that of the jet at the inlet. The nozzle-to-plate distance (measured along the jet axis) is set to 5D, with D the nozzle diameter. In order to highlight the curvature effects, the present results are compared to a previous study of jet impinging on a flat plate. The specific influence of wall curvature is investigated through a frequency analysis based on discrete Fourier transform and dynamic mode decomposition. We found that the peak frequencies of the heat transfer also dominate the dynamics of primary vortices in the free jet region and secondary vortices produced by the interaction of primary vortices and the target plate. These frequencies are approximately \(30\%\) lower than those found in the reference study of impinging jet on a flat plate. Imperceptible differences were instead found in the time-averaged integral heat transfer.