Julien Pellé

Review of fluid flow and convective heat transfer within rotating disk cavities with impinging jet

Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steadystate (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk, rotor-stator systems without and with impinging single jets, as well as multiple jets. Conclusions to the review outline perspectives of the further extension of the investigations of different kinds of the rotor-stator systems and their applications in engineering practice.

Thermal Optimization of a High-Power Salient-Pole Electrical Machine

An optimization of the thermal behavior of a high-power salient-pole electrical machine is presented. Temperatures are calculated with the lumped method, which provides the thermal trends with relatively low computational cost. This model is used to define an aggregated objective function of our nonlinear thermal optimization problem by combining the mean solid temperature with the maximum temperature criteria. The 13 design variables correspond to the main volumetric flow rates in the electrical machine, which are bounded and subjected to a nonlinear constraint, assuming a fixed geometry. Two MATLAB optimization algorithms were tested: the Active-set (FMINCON solver) and the genetic algorithm (GA). Due to the strong nonlinearities of the model and the resulting nonconvex optimization problem, the GA is likely to give better results. Minimizing the mean solid temperature was demonstrated to be more important than the maximum temperature criterion. A strategic flow configuration is found to send fresh air to the second half of the cooling circuit, where air usually arrives heated. This optimal configuration provides better cooling than its current modeled configuration. This methodology should be of interest during the development phase.

Mock-Up Study of the Effect of Wall Distance on the Thermal Rating of Power Cables in Ventilated Tunnels

Power transmission through power cables installed in ventilated tunnels is increasingly used worldwide and offers a complex thermal environment. Established correlations currently in use have been deduced from a nonfully developed turbulent flow and the effect of the proximity to a tunnel wall is not accounted for. This paper details the experimental and numerical investigations conducted on a mock-up of the heat transfer from a single cable in a fully developed turbulent airflow, with emphasis on the effect of the cable spacing from the tunnel wall. Nusselt numbers have been compared for different spacing and Reynolds numbers. The overall heat transfer is found to be meaningfully lower than in previous studies as only a third of the heat transfer is found, possible explanation of these differences are given in this paper. A threshold value is observed for the heat transfer while the cable rating depreciation is more gradual. The radiative heat exchange is found to be up to 30% of the total heat loss. An improved cooling law for the case of a single cable in tunnel taking into account the proximity of the wall has been developed from this study and confronted to the experimental and simulated data.

Mass and Heat Transfer Inside the Air Gap of a Discoidal and Unshrouded Rotor Stator System With a Jet Impingement

Mass and heat transfer are experimentally investigated in a discoidal and unshrouded rotor-stator cavity where an air jet passes through the stator and impinges on the rotor center. Using a jet impingement is a way to bring fresh air inside the air gap and to increase shear stresses and so heat transfer over the rotor. This study focuses on comparisons between heat transfer coefficients and velocity fields obtained inside the air gap for the case of a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Two jet Reynolds numbers ranging from 16000 to 42000 and three rotational Reynolds numbers between 30000 and 516000 are considered. Mass transfers are investigated by Particle Image Velocimetry technique while the radial distribution of heat transfer coefficients over the rotor is obtained using a thick wall method and temperature measurements by infrared thermography.© 2012 ASME

Flow Structure and Heat Transfer Numerical Study in a Rotor-Stator System Air-Gap

This paper deals with flow structure and heat transfer modeling in a two coaxial disk air-gap. Numerical estimations for the local Nusselt number on the rotor, for the radial and tangential velocities are compared with experimental results obtained using PIV and infrared thermography. Models used for the numerical approach are then validated for a turbulent Reynolds Number.© 2005 ASME