Study of high aspect-ratio dual intersecting jets and the installation effect on control authority

Abstract

With an unprecedented surge in the number of individuals utilizing electric vehicles for commuting across the globe, it is becoming critical to immediately deliver an adequate and range-friendly degree of thermal comfort in car cabins to help drivers remain focused and attentive. The research presented in this thesis is part of the development work carried out by the Aerothermal team at Tesla. The team aims to better understand high aspect ratio subsonic jets, particularly intersecting twin jets, to ventilate the vehicle's passenger compartment.

The intersecting twin jet has recently captured significant attention from the Aerothermal team for several reasons. Firstly, it provides the ability to actively control the flow angle from the HVAC unit into the vehicle cabin without requiring direct interaction with the vent. Additionally, it facilitates the flushing of the vent outlets with the A-class surfaces in the vehicle interior, helps achieve a simple and minimalist design for the instrument panel and other interior surfaces that align with Tesla's design language

The objective pursued in this thesis is to investigate the physics represented by the bulk flow characteristics of intersecting twin jets, and to scrutinize the installation effect on the merging jet, focusing on the influence of the installation surface offset height. This objective is achieved by characterizing the evolution of large-scale flow structures in High AR intersecting twin jets at moderate Reynolds numbers experimentally using planar Particle Image Velocimetry (PIV) in both installed and uninstalled conditions. Once accomplished, the experimental results are then used to help select, validate, and calibrate the appropriate RANS turbulence model.

The experimental results show that the intersecting jets converge before merging and forming a single jet. This jet behaves like a single jet emanating from a more recessed origin. The variation of the flow ratio between the two nozzle outlets results in varying the jet angle. The study reveals that the placement of the surface impacts the jet angle and velocity and introduces a circulation zone that affects the jet's behavior and direction. The surface's impact depends on the offset distance, length, and profile of the surface. The results also suggest that accurate computational prediction of the jet characteristics requires high mesh resolution and an appropriate selection of turbulence intensity. Among the four turbulence models assessed, the k-omega SST model is found to be adequate for the application, although it exhibits some numerical hysteresis. Overall, the findings provide insights into the dynamics of jet-surface interactions and can guide the design of systems involving such flows.