Numerical Characterization of Pressure Drop Across the Manifold of Turbine Casing Cooling System

Abstract

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 ¼ 1.01-1.6, t/d ¼ 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.

Aerothermal Analysis of a Turbine Casing Impingement Cooling System

“…Even developed referring to circular cross-section manifold geometries, DaSoghe and Andreini [18] proved the correlation reliability also in case of squared manifold geometries.…”

“…By using the provided experimental data (see [17]) and validated CFD calculations, Andreini and DaSoghe [9] have developed an empirical correlation for the prediction of the impinging holes discharge coefficient: it 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. Recently, the authors have revised this correlation to make it sensible to the nozzle length-todiameter ratio [18]. The second test rig, aims to evaluate the heat transfer coefficient and the adiabatic effectiveness of a multijet impingement array (for which the undercowl flow is considered) which reproduces an active clearance control system of a commercial aircraft.…”

“…The correlation for the C d parameter considered in this study has been recently developed by DaSoghe and Andreini [9,18]. The expression is the result of an extensive CFD analysis: it expresses the C d of each impingement hole as a function of the ratio between the hole and the manifold mass velocity (MVR), the nozzle length-to-diameter ratio (t/d) and the local value of the β L ratio.…”

“…For further details about the presented correlation and the related validation study, refer to Andreini and DaSoghe papers [9,18].…”

Velocity pick-up and discharge coefficient for round orifices with cross flow at inlet

“…The maximum discrepancy in discharge coefficient between CFD and measurement is about 10% over a range of conditions. Also using the SST k ω − model, Da Soghe and Andreini [21] have studied discharge from a duct through multiple orifices aligned at right angles to the flow. CFD results from this study and earlier work by the same authors was used to produce a correlation for orifice discharge coefficient taking into account inlet cross flow, orifice pressure ratio, and orifice L/D ratio.…”