The dispersion of a high temperature air jet in a bluff body wake

Stephens, Isaac ORCID: 0000-0001-5316-7662, Owen, Ieuan and White, Mark ORCID: 0000-0002-8611-9525
(2023) The dispersion of a high temperature air jet in a bluff body wake. In: International Heat Transfer Conference, 2023-8-14 - 2023-8-18, Cape Town, South Africa.

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This paper will describe the results of an experimental study in which a hot air jet was discharged from a circular orifice on the upper face of a cuboid mounted on the floor of a wind tunnel and exposed to a cross-flow with ambient temperature. While there have been numerous studies into the discharge of a heated jet from a flat surface into an undisturbed cross-flow, there appears to be no such studies for a jet being discharged into the highly turbulent flow over a bluff body. The face of the cuboid was placed normal to the wind tunnel air flow; its dimensions are 200mm × 200mm and its length is 400mm. The hot air jet, with temperatures up to 143°C was discharged from a 25mm diameter orifice located at the centre of the top surface of the cuboid. The jet velocities were up to 15.8m/s while the cross flow was up to 3.9m/s, measured upstream from the bluff body. The scenario being modelled is the discharge of exhaust gases from a ship’s gas turbine engine and the dispersion of the hot jet as it mixes with the turbulent air flow over the ship’s superstructure. The practical application of the study is the impact of the hot exhaust on the ship’s helicopter when it encounters the heated, lower density, exhaust plume. The simplified experiment will provide benchmark data for comparing with the results from an equivalent Computational Fluid Dynamics (CFD) study. In the wind tunnel, the cross-flow separates from the edges of the front face of the cuboid, forming a recirculation zone over the top surface, and generating a turbulent three-dimensional wake downstream. As the heated jet emerges from the orifice, it is deflected by the cross-flow and the two flows mix. The jet trajectory becomes nearly horizontal and the temperatures within the plume diminish quickly due to the turbulent mixing. Dimensional analysis shows that, for momentum-dominated turbulent flows, the non-dimensional temperature and the trajectory of the jet plume are related to the ratio of the momentum flux of the jet to that of the cross-flow. Experiments were therefore carried out for a fixed momentum flux ratio but with three different sets of temperatures and velocities for the jet and cross-flow. Measurements of temperature profiles in the plume downstream of the jet confirm the dimensional analysis. To set the scene, the paper will illustrate the dispersion of hot gas turbine exhaust gases as they mix with the turbulent air flow over a naval frigate using the results of a CFD study. The details of the experiment and the results will be provided and comparisons will be made with a CFD analysis of the wind tunnel experiment.

Item Type: Conference or Workshop Item (Unspecified)
Divisions: Faculty of Science and Engineering > School of Engineering
Depositing User: Symplectic Admin
Date Deposited: 31 May 2023 08:11
Last Modified: 17 Nov 2023 09:34