This book is a printed edition of the Special Issue Intermittency and Self-Organisation in Turbulence and Statistical Mechanics that was published in Entropy

The primary objective of this study is to evaluate the accuracy of using turbulence models to predict entropy generation rates in bypass transitional flows under various pressure gradients in a spatially growing boundary layers over a flat plate. Entropy generation rates in such flows are evaluated using CFD methods. Various turbulence models are assessed by comparing results with DNS data and two recent CFD studies. 3D bypass transition simulations are also performed using LES and IDDES models. Results show better agreement with DNS than any previous RANS studies. The k-o 4eqn. transition model shows closest agreement to DNS data for 2D flow. The SGS models are highly dissipative and LES will require much finer grid within boundary layer region and freestream. These models fail to predict bypass-transition accurately due to lack accurate unsteady fluctuations and grid resolution. Certain limitations and issues are identified and recommendation are made for future studies.

The principal purpose of this study is to better understand the pointwise entropy generation rate in bypass, transitional, boundary-layer flow. The experimental work herein, utilized particle image velocimetry (PIV) to measure flow along a flat plate. The flow past the flat plate was under the influence of a ''negligible'' zero pressure gradient; followed by the installation of an adverse pressure gradient. Further, the boundary layer flow was artificially tripped to turbulence (called ''bypass'' transition) by means of elevated freestream turbulence. The pointwise entropy generation rate was seen to behave similar to that of published CFD and DNS results. The observations from this work show the decrease of viscous contributions to entropy generation rate through the transition process; while the turbulent contributions of entropy generation rate greatly increase through the same transitional flow. A basic understanding of pointwise entropy generation rate over a flat plate is that a large majority of the contributions come within a y +

Conditionally-sampled boundary layer data for an accelerating transitional boundary layer have been analyzed to calculate the entropy generation rate in the transition region. By weighing the nondimensional dissipation coefficient for the laminar-conditioned-data and turbulent-conditioned-data with the intermittency factor the average entropy generation rate in the transition region can be determined and hence be compared to the time averaged data and correlations for steady laminar and turbulent flows. It is demonstrated that this method provides, for the first time, an accurate and detailed picture of the entropy generation rate during transition. The data used in this paper have been taken from detailed boundary layer measurements available in the literature. This paper provides, using an intermittency weighted approach, a methodology for predicting entropy generation in a transitional boundary layer.