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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

ADVANCED STATISTICAL ANALYSIS OF THE COLLISION OF WALL JET WITH A BOUNDARY LAYER

DOI: 10.1615/TFESC1.asp.012935
pages 151-163

Andre R. R. Silva
Aerospace Sciences Department, University of Beira Interior, Rua Marques Avila e Bolama, 6201-001 Covilha, Portugal

Miguel R. O. Panão
ADAI-LAETA, Mechanical Engineering Department, University of Coimbra, Rua Luis Reis Santos, 3030-788 Coimbra, Portugal

Jorge M. M. Barata
Aerospace Sciences Department, University of Beira Interior, Rua Marques Avila e Bolama, 6201-001 Covilha, Portugal


KEY WORDS: VSTOL, Ground Vortex, Wall Jet, Boundary Layer, Statistical Analysis, Finite Mixtures, Bayesian Approach, Markov Chain Monte Carlo

Abstract

Laser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are analyzed using advanced statistical tools. Namely, finite mixtures of probability density functions, which determine the best fitting using a Bayesian approach based on a Markov Chain Monte Carlo (MCMC) algorithm. This approach takes into account eventual multimodality and heterogeneities in velocity field distributions. Therefore, it provides more complete information about the probability density function of multimodal velocity distributions and allows the identification of characteristic velocities in the heterogeneous data. The experiments are performed for a wall jet-to-boundary layer velocity ratio of 2, and include mean and turbulent velocity characteristics along the two normal directions contained in planes parallel to the nozzle axis. The results, which have relevance to flows encountered by VSTOL aircraft, quantify the structure of the complex ground vortex flow. The results revealed that in the collision zone the rms velocity fluctuation appears to be overestimated for the horizontal component, probably due to the measured velocity range, oscillating between positive and negative values. The results revealed that finite mixture was able to accurately reconstruct a mathematical function describing the probability distribution obtained experimentally. The results shows that U and u'rms rms provide an idea of the flow dynamics, their use is limited and an important amount of information associated with the highly curved flow complexity is lost, preventing a more accurate description of turbulent structures emerging from the collision of wall jet with a boundary layer.

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