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The ultra-high bypass ratio geared turbofan is a key concept to reduce the environmental impact of the next generation aircrafts. The increase in rotational speed of the low-pressure turbine (LPT) enabled by the geared architecture offers potential benefits in efficiency and considerable savings in engine weight, overall dimension, and cost. High-speed LPTs operate at transonic exit Mach numbers and low Reynolds numbers. For this combination of operating conditions, where compressibility influences the blade aerodynamics and loss mechanisms, there is a critical lack of openly available detailed experimental data concerning the combined effects of unsteady wakes, purge streams, leakages, and secondary flows for CFD models validation. The current research project focuses on the full characterization of an experimental test case concerning the impact of unsteady wakes and purge flows on the blade aerodynamics and loss mechanisms in a high-speed LPT cascade tested at engine-scaled conditions. The extensive experimental dataset is collected in an open-access database, providing novel validation material for comparison with numerical computations. In this two-part paper, a comprehensive study on the design, commissioning and testing of a transonic low-pressure turbine blade at on and off-design is presented. Part I describes the design of components and accurate instrumentation required to investigate steady quasi-3D flows in a linear cascade environment at low-Reynolds and transonic exit Mach numbers. A novel concept to perform blade radial traverses to obtain spanwise distributions of high-resolution blade measurements is presented. The repeatability and periodicity of the rig flow conditions are demonstrated. This work critically evaluates the methodology used for the design and adaptation of the existing rig for testing of unsteady three-dimensional flows in linear cascade experiments.

This paper tackles the issue of frost formation in air-to-air heat recovery devices dedicated to single room ventilation by means of both numerical simulations and experimental approaches. In such heat exchangers, it is commonly known that the formation of a frost layer on the surface generates an additional thermal resistance and a flow section reduction, which leads to an overall degradation of the overall unit performance. This paper proposes a three-zone model, considering a dry, a wet and a frost zone, by determining the location of moving boundaries. Each zone is handled independently and the relative proportion of each zone is determined by means of the exchanger wall temperature. Besides this frost model, a defrost model is also envisaged. Once validated with experimental data collected on a U-flow-type heat exchanger, the developed model is used to implement different strategies to reduce or prevent frost formation in the exchanger. Based on three different criteria, these strategies are compared with each other to evaluate their benefits and drawbacks. The criteria give information on the energy efficiency of the ventilation, on the air renewal quality and on the pressure balance between the inside and the outside of the building.

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The present paper focuses on the development steps of heat exchangers dedicated to single room ventilation unit with heat recovery (SRVHR) by proposing a numerical approach. A methodology is suggested in order to determine the best trade-off between hydraulic and thermal performance given a specific geometry. The methodology consists in a mapping of the coefficient of performance (COP) of the unit. The latter is defined as the ratio between recovered heat and the fan energy use, given a specific indoor/outdoor temperature difference. However, the energy performance should not be the only criterion to be taken into account in the frame of the design steps of a heat recovery exchanger: technical, economic and acoustic aspects should also be considered. This numerical methodology is illustrated by means of a real example of a newly developed heat exchanger dedicated to a SRVHR. The optimization is first performed while using a semi-empirical model (based on the use of correlations and on a spatial division of the studied heat exchanger). The semi-empirical model allows for the creation of a COP map in order to identify the most effective geometry parameters for the heat exchanger. The decision concerning the final geometry is made accounting for the so-called technical, economic and acoustic considerations. A discussion on some parameters needed for the COP establishment is also proposed.