Numerical analysis of low crossflow impingement cooling geometry

Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature and a continuous reduction of turbine blades cooling flow rate, justified by a corresponding increase of cycle efficiency and power output. An accurate design of the cooling system and a strong knowledge of heat transfer phenomena developed inside a gas turbine vane or blade is mandatory. In this paper an innovative impingement geometry for vanes applications is presented. The goal of this improved impingement is to avoid negative effects of crossflow coming from the previous jets in a configuration characterized by a large number of consecutive rows. After the geometry definition, CHT (Conjugate Heat Transfer) CFD simulations results is presented where a comparison of the innovative and a standard impingement geometry is conducted. The two different geometries share same global dimensions and same air consumption, so a comparison can be considered significant. Subsequently CFD analyses are compared to a decoupled procedure for evaluating metal temperatures: in this methodology the internal cooling system is modeled by an in-house one-dimensional thermo-fluid network solver, external heat loads and pressure distributions are evaluated through 3D CFD and heat conduction through the solid is computed through a 3D FEM solution. The validation of such procedure allows to run many different geometry configurations with a remarkable savings in computational costs. These runs are performed in order to find the main geometrical characteristics that can reduce metal temperatures on the plate, maintaining global dimensions and air consumptions. In the second part of the paper the innovative cooling geometry is applied in a second stage gas turbine vane, replacing the existent impingement plate. The results, carried out with a procedure described above, shows a significant reduction in external metal temperature. The performed analysis allow to underline how the presented innovative configuration can improve heat transfer in a gas turbine vane due to a strong reduction of the negative effect of the crossflow produced by the jets. Multiple runs with a very low computational time are carried out using the procedure described in [2], defining which are the most influential geometrical parameters for a good design of the presented low crossflow impingement.