The Modelling of a Turbulent Near Wake Using the Interactive Hypothesis.

摘要

A semi-empirical mathematical model for a turbulent near wake has been developed within the framework of an 'interaction hypothesis' suggested by Bradshaw. The near wake behind an airfoil has been treated as a 'complex' shear flow consisting of two neighboring simple shear layers with distinct but overlapping shear stress profiles of opposite signs. The present model utilizes the mean momentum and continuity equations together with two shear stress transport equations derived from the turbulent kinetic energy equation. By relating the shear stresses to the local turbulence equantities, closure for the governing systems is achieved without the use of the eddy viscosity concept. The shear stress is therefore no longer required to vanish at the velocity extremum. The model has been compared to the experimental data of Chevray and Kovasznay and good agreement has been obtained. A comparison with the asymmetric cascade wake data of Raj and Lakshminarayana is also presented. Our calculations have validated the basic philosophy of an interactive approach in the study of near wakes. However, it also clearly demonstrates that the accuracy of certain empirical functions used to define the turbulence structure has a direct impact on the success of this or any other calculation method. (Author)