Wake aerodynamics for 2D bluff bodies.

摘要

Wake aerodynamics of bluff bodies is a vast and challenging domain and new theoretical, experimental or numerical approaches to this subject are expected to produce a great impact on a large palette of academic and practical topics.;A new description of the wake turbulent field is introduced in the present doctoral research. This wake model is further on applied to loading problems on isolated and buffeted structures.;Following a comprehensive review, a wake turbulence model is defined. Making use of a simple "variable filtering" eduction method, focusing on coherent turbulence rather than on random turbulence, and employing flow dimensions rather than body dimensions the similarity (self preservation) and universality (independence of constraint) of turbulence profiles is demonstrated for both smooth and turbulent flows. Longitudinal (downstream) variation of different wake parameters is introduced and used to demonstrate the validity of the vortex eduction method. CFD simulations by FLOW3D code are presented for different shapes for both steady and transient scenarios employing various turbulence models. Results are compared with present and other experimental data.;Direct applicability of the wake model for buffeting problems is found and tested. As a primary step an improvement of existing self-induced loading models for isolated structures is presented. A modified notched-hodograph theory is employed for drag and fluctuating lift modeling and comparison to experiment is provided. Based on vorticity-circulation calculations, the wake geometry for various 2D bluff bodies is analysed and the notched hodograph theory is completed with a r.m.s. lift model (L Model) with improved simulation qualities in terms of results and applicability.;A detailed investigation of the buffeting loading problem for sharp edged bluff bodies is addressed. Tandem and staggered configurations are studied in both smooth, large scale and small scale turbulent flows for various shapes and geometries. Characterisation and partition of the buffeting domain is provided. Semi-empirical models for force coefficients and Strouhal number are defined for the upstream wake inertial domain. The term 'inertial' is used somewhat loosely here but it defines the part of the wake field for which the body related turbulence production (close wake) and the dissipation effects (far wake) are in a certain equilibrium. This domain also corresponds to the similar and universal wake model previously defined (Chapter 2). Spectral modeling is also introduced and a new approach is proposed for drag loading so that wind-load linear dependence is extended. Collateral to this, an interesting centre-wake wind spectral analysis is provided and it is shown how transition from sub-inertial to inertial spectral behaviour is enhanced by free-stream turbulence. LASER flow visualisations are employed for a better understanding of critical interference regimes such as bi-stable flow situations.;Finally an original classification of 2D bluff bodies is proposed and this relies on both wake flow and wake loading aerodynamics.