Laura Villafañe

Development of a transonic wind tunnel to investigate engine bypass flow heat exchangers

The design of a new transonic wind tunnel to reproduce bypass aero-engine flow conditions is described. This study has been driven by the interest to investigate and optimize the aero-thermal effects of an air/oil integrated surface heat exchanger placed at the inner wall of the secondary duct of a turbofan. The test section of the intermittent wind tunnel consists of a complex three-dimensional (3D) geometry. The flow evolves over the splitter, duplicated at real scale, as it does in the engine, guided by helicoidally shaped lateral walls. Numerical flow analyses have been used to guide the design of the complete wind tunnel. Zero-dimensional models have been developed to recreate the wind tunnel behaviour. Two- and three-dimensional computations have been performed to optimize the test section and the inlet guide vanes that duplicate the flow downstream of the engine fan. The reproduction of the bypass flow structure has been numerically analysed. Flow computations with and without the presence of instrumentation in the test section have been contrasted. Additionally, the influence of an aerodynamic probe on the flow has been studied numerically. This study should lead to improvements in the thermal management of future aircraft power plants, particularly by taking benefit of the cold bypass air to refrigerate the lubrication oil, without penalizing the propulsive efficiency.

Three-dimensional (3D) inverse heat flux evaluation based on infrared thermography

Inverse methods in heat transfer are generally associated with the estimation of unknown heat fluxes on inaccessible surfaces, based on temperature measurements performed on the accessible walls. In the present application, an inverse heat conduction method was developed that uses temperature measurements performed by infrared thermography. The three-dimensional (3D) transient inverse heat transfer problem was solved by using an iterative regularisation with a conjugate gradient method. The inverse solver was coupled with a finite element commercial code. The efficiency of the method was demonstrated through numerical simulations and experimentally validated in a simplified set-up.

Experimental Investigation of Engine Bypass Flow Behavior in the Presence of Surface Heat Exchangers

Ongoing engine developments require advanced thermal management technologies to handle the increasing demand of refrigeration and lubrication. As the thermal capacity of the oil lubricant and coolant circuits becomes saturated, cooling sources in addition to the conventional fuel based oil cooling systems are essential for the engine operation. This research is focused in the experimental investigation of the turbofan bypass flow behavior in the presence of finned heat exchangers oriented with the mean flow direction. Engine testing methods alternative to flight testing were developed for this purpose. A new test facility reproducing the engine bypass flow at cruise velocities and take off atmospheric conditions was built to study the flow phenomena. Different measurement techniques were adapted to the requirements of the flow and wind tunnel characteristics. Particular attention was dedicated to the development of a multi-hole probe and a data reduction methodology providing accurate results in a wide angular range at transonic conditions. The flow development along the bypass channel flow was characterized in the presence of different heat exchanger geometries, and compared to the flow development in the absence of heat exchangers.© 2014 ASME

Development of Experimental Techniques for the Characterization of Helicoidal Fin Arrays in Transonic Flow Conditions

The current research focuses on the aerodynamic investigation of the three dimensional turbofan bypassflow and its interaction with a finned air/oil surface heat exchanger integrated at the inner wall of the secondary duct. This paper addresses the experimental methodology employed in a new transonic facility characterized by a complex 3D test section. The development of accurate and relatively short time response measurement techniques is essential for the evaluation of the flow by means of map measurements at different locations along the test section. Flow angles, total and static pressures are computed using a new methodology for the processing of the pressure readings acquired by means of hemispherical five-hole probes. The sensibility of the probes and the errors on the angle determination are analyzed. Errors lower than 0.4 deg. for the determination of yaw and flow angles are obtained. The response of the shielded thermocouples designed for the temperature measurements are studied by means of conjugate heat transfer simulations. The numerical methodology is described and the steady and transient temperature effects evaluated. An innovative procedure for shear stress measurements based on oil-dot techniques is discussed and applied on a representative test bench for validation. Results are comparable with theoretical and empirical wall shear stress correlations for the case of a flat plate in subsonic flow conditions.