Étude par CFD de l'interaction jet-surface dans un banc d'essais servant à modéliser le dégivrage au sol des avions

Abstract

According to the regulations, aircrafts are required to fly with lifting surfaces free from any solid contamination. This solid contamination can be frosted contaminants, ice or accumulation due to freezing rain or because of below-freezing fuel in the wing tanks. Propylene glycol jets in air are widely used in the ground de-icing to remove ice accretion on aircraft. The jets impact the aircraft surface and heat transfer and momentum forces remove accreted ice. This study investigates momentum forces and heat transfer created by turbulent liquid jet impinging on a horizontal plate at temperature below freezing point with CFD. The version 11.06 of STAR-CCM+ is used for CFD ground de-icing simulation. Validation cases are a free axisymmetric steady air jet impinging on a flat heated surface to cool, the phase change of an ice block in natural convection and case of multiple jets impinging on a curved surface. The main geometry of the CFD modelling of de-icing is a free jet coming out of a nozzle, inclined with horizontal plane and all contained in a rectangular block. The mesh is refined with polyhedral cells in the diffusion zone of the jet at the nozzle exit. The mesh is also refined by rectangular cells in the stagnation zone where the liquid film is formed. All y+ wall treatment is applied to model the boundary layer on the jet impinging surface. Local Nusselt number curves are in agreement with the experimental results, found in the literature, of Lee et al. (1999) and Fénot et al. (2008). Various turbulence models have been compared and Elliptic Blending k-ε is able to predict the second peak of heat transfer due to near wall jet. It is conjectured that the largest heat transfer rate is located at the jet impinging point and the second peak of the local Nusselt number is near the impinging point. The study of momentum forces allows noting that the heat transfer maxima (local Nusselt number) at the stagnation point decrease while increasing Reynolds number. The phase change case of an ice block in natural convection is validated with experimental data of Virag et al. (2006). This work is novel in that it first proposes a CFD model of ground de-icing jet. The hypotheses are that flow due to impinging oblique unconfined jet on a horizontal plate depends on geometric and physic parameters. These parameters are the nozzle diameter and pressure, the jet temperature, inclination angle and distance to plate (standoff). A parametric study allowed evaluating the influence of the variation of these parameters on three variables. These variables are the de-icing velocity; the liquid spreading coefficient and the groove depth created by the jet impingement. The results were compared with Chakraborty et al. (2009) experience for liquid film velocity and Guha et al. (2011) experience for the spreading coefficient. Thus the CFD approach presented is able to simulate the 3D de-icing regarding the jet from its exit from the nozzle until the formation of the liquid film on the impinging surface. Finally the parametric study evaluated the sensitivity of the numerical results to the geometric and physic parameters.

Date	20 Dec 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Morency (Supervisor)