Journal of Turbomachinery 135(3), May 2013

Transaction of ASME Turbo Expo 2012 – GT2012-69581

An experimental survey on a state of the art leading edge cooling scheme was performed to evaluate heat transfer coefficients (HTC) on a large scale test facility simulating a high pressure turbine airfoil leading edge cavity. The test section includes a trapezoidal supply channel with three large racetrack impingement holes. On the internal surface of the leading edge, four big fins are placed in order to confine impingement jets. The coolant flow impacts the leading edge internal surface, and it is extracted from the leading edge cavity through 24 showerhead holes and 24 film cooling holes. The aim of the present study is to investigate the combined effects of jet impingement and mass flow extraction on the internal heat transfer of the leading edge. A nonuniform mass flow extraction was also imposed to reproduce the effects of the pressure side and suction side external pressure. Measurements were performed by means of a transient technique using narrow band thermochromic liquid crystals (TLCs). Jet Reynolds number and crossflow conditions into the supply channel were varied in order to cover the typical engine conditions of these cooling systems (Rej=10,000−40,000Rej=10,000-40,000). Experiments were compared with a numerical analysis on the same test case in order to better understand flow interaction inside the cavity. Results are reported in terms of detailed 2D maps, radial-wise, and span-wise averaged values of Nusselt number.

http://turbomachinery.asmedigitalcollection.asme.org/article.aspx?articleid=1672756

https://www.researchgate.net/publication/326263417_Heat_Transfer_Measurements_in_a_Leading_Edge_Cooling_Geometry_under_Rotating_Conditions

Journal of Turbomachinery 135(3), Mar 2013

Transaction of ASME Turbo Expo 2012 – GT2012-68787

An array of jets is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found in the impingement cooling systems of turbine blades and vanes or in the turbine blade tip clearances control of large aero-engines. In order to correctly evaluate the impinging jet mass flow rate, the characterization of holes discharge coefficient is a compulsory activity. In a previous work, the authors have performed an aerodynamic analysis of different arrays of jets for active clearance control; the aim was the definition of a correlation for the discharge coefficient (C_d) of a generic hole of the array. The developed empirical correlation expresses the (C_d) of each hole as a function of the ratio between the hole and the manifold mass velocity and the local value of the pressure ratio. In its original form, the correlation does not take in to account the effect of the hole length to diameter ratio (t/d) so, in the present contribution, the authors report a study with the aim of evaluating the influence of such parameter on the discharge coefficient distribution. The data were taken from a set of CFD RANS simulations, in which the behavior of the cooling system was investigated over a wide range of fluid-dynamics conditions (pressure-ratio = 1.01–1.6, t/d = 0.25–3). To point out the reliability of the CFD analysis, some comparisons with experimental data were drawn. An in depth analysis of the numerical data set has led to an improved correlation with a new term function of the hole length to diameter ratio.

http://turbomachinery.asmedigitalcollection.asme.org/article.aspx?articleid=1672753

https://www.researchgate.net/publication/287511742_Numerical_characterization_of_pressure_drop_across_the_manifold_of_turbine_casing_cooling_system

ISAIF 10-58, 2012

Turbine blade tip clearances control of large aero-engines is currently performed by impinging fan air on the outer case flanges. The present paper reports a numerical and experimental survey aimed to evaluate the heat transfer coefficient of six arrays of impingement holes drilled on circular ducts. Tested geometry replicate the impingement tubes and the by-pass duct used in active control clearance systems. Tube internal diameter is D=12mm, cooling holes diameter d=1mm, span-wise pitch is Sx/d = 12. In order to simulate the flow of the by-pass duct, the impingement arrays are inserted inside a tunnel that replicates the typical shape of a real engine by-pass duct. Numerical and experimental tests were conducted varying both the mainstream Reynolds number and the jet Reynolds number in a range typical of effective engine operative conditions (Rej=2000-10000, beta=1.01-1.20).