MARS - Manipulation of Reynolds Stress for Separation Control and Drag Reduction
Overview
Background & policy context:
Reynolds stress is the most important quantity affecting the mean flow as it is responsible for a major part of the momentum transfer in the wall bounded turbulent flow. It has a direct relevance to both skin friction and flow separation. Manipulation of the Reynolds stress can directly lead to changes in the viscous stress at the wall so as to effectively control the flow for effective flow control. However, there is a lack of current understanding of the inter-relationship between the various flow control devices and the Reynolds stresses in the flow field they produced.
Objectives:
An improved understanding can potentially significantly improve the effectiveness of flow control as the Reynolds stresses are closely related to the flow behaviour at the surface for effective separation control or drag reduction.
A variety of control devices are available and new ones are invented, but which one for what purpose is an open question yet to be fully answered. The MARS project proposes to reverse that process and considers the long term goal of controlling dynamic structures that influence the Reynolds stress that changes the mean flow. This radical approach recognises we are still some way away from hardware to implement it at flight scales but if successful, would establish a first important step towards our ultimate ambition.
Methodology:
The focus of MARS will be on the effects of a number of active flow control devices on the discrete dynamic components of the turbulent shear layers and the Reynolds stress. From the application point of view, MARS provides a positive and necessary step in the right direction wherein it will demonstrate the capability to control individual structures that are larger in scale and lower in frequency compared to the richness of the time and spatial scales in a turbulent boundary layer. MARS will investigate active flow control means rather than passive controls.
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