Experimental and Numerical Analysis of Multiple Impingement Jet Arrays for an Active Clearance Control System

Abstract

The turbine blade tip clearances control in large aero-engines is currently performed by means of impinging fan air on the outer case flanges. The aim of the present study is to evaluate both the heat transfer coefficient and the adiabatic thermal effectiveness characteristics of an enginelike ACC system, and in particular, to comprehend the effects of the undercowl flow on the impingement jets. The considered geometry replicates the impingement tubes and the by-pass duct used in active control clearance systems. The tube's internal diameter is D = 12 mm, the cooling hole's diameter is d = 1 mm, and the span-wise pitch is Sy/d=12. In order to simulate the undercowl flow, the impingement arrays are inserted inside a tunnel that replicates the typical shape of a real engine by-pass duct. Tests were conducted varying both the mainstream Reynolds number and the jets Reynolds number in a range typical of real-engine operative conditions (Rej=2000-10000, β=1.05-1.15). Numerical calculations are finally proposed to point out if CFD is able to confidently reproduce the experimental evidences.

Experimental Investigation of a Complex System of Impinging Jets Using Infrared Thermography

“…These deviations do not result from an uncertainty of their measurement technique, but from the definition of a correlation which results from a great data set and which is therefore valid in a wide range of geometrical and fluid flow conditions. The conditions of this specific case from Goldstein and Seol [6] define the limit of the validity range of Equation (11), whereby the conditions are closest to the present setup and the comparison is the fairest. While in Figure 11, the correlation predicts higher maxima in the stagnation region compared to the experimental results from the present investigation, the Nusselt number is slightly lower at y/D = 6 due to a steeper gradient over y/D.…”

“…A common measurement technique for the experimental investigation of impinging jet configurations is the use of thermochromic liquid crystals (TLC). Geers et al [10] and Andreini et al [11] used wide-band TLC at an electrically heated plate predicting the heat transfer from an array [10] and rows [11] of impinging jets at steady-state conditions. For steady-state measurements, the influence of the surroundings has to be known precisely.…”

Improved Modeling Capabilities of the Airflow Within Turbine Case Cooling Systems Using Smart Porous Media

“…The aim of the TCC systems is to optimize tip clearance across different engine operating conditions [4] and around the casing circumference. To achieve this a key requirement is to provide a near-uniform delivery of cooling air to the turbine casing.…”

“…This type of porous media approach has been used in several other fields including the modelling of catalytic converters, heat exchangers, concrete flow and fuel injectors (see [6 -12]). There have also been multiple studies on impingement flows such as flow through perforated plates [13], flow through impingement cooling holes employed as film cooling in turbine blades [14][15][16], combustor liners [17][18] and TCC systems [4,19].…”

“…Andreini et al[4]). Convergence was judged by monitoring the residuals within the solutions and the flow parameters at the inlet of the domain.All cases with impingement cooling hole features utilized a compressible solver as the flow in the holes exceeds a Mach number of 0.3.…”