Active control and dynamic modeling of the turbulent boundary layer via direct manipulation of large-scale structure
Abstract
The turbulent boundary layer (TBL) is one of the main factors influencing both aircraft and marine vessel performance, affecting flow properties like skin friction drag, sound radiation and flow separation, to name a few. A better understanding of the non-linear interaction between the various structures in the TBL and new models of their dynamic mechanisms will be instrumentalin designing novel closed-loop active control strategies to effectively manipulate the boundary layer in order to reduce the drag, change the acoustic signature etc. Effective control of TBLs is crucial to improving the performance of various vehicles relevant to future Naval capabilities (ocean vessels, fixed-wing, rotary-wing, and V/STOL aircraft). An impediment is that we currently lack a complete understanding of the non-linear dynamics in the TBL, including the interactionbetween the outer large-scale structure (LSS) and the structures in the near-wall region that are believed to be fundamental to the TBL dynamics. In this work we will investigate this critical interaction between the large shear-layer-likestructures and wall-turbulence by independently disrupting/modifying either the LSS or the nearwall dynamics using a novel combination of experimental studies and reduced order model-based simulation and analyses. The underlying flow mechanism that the approach exploits is the sensitivity of shear layer structure to low-amplitude excitation arising from an inherent inflectionalinstability mechanism. The experimental studies will leverage novel actuation technologies developed at the University of Notre Dame, namely the ALSSA and SLIPPS actuators that have shown the ability to modify the outer LSS and achieve significant reduction in friction drag, respectively. In the first series of experiments ALSSA will be used to directly manipulate LSS in the outerregion of the TBL and we will investigate the resulting effect on near-wall structures and overall TBL dynamics. In the second set of the experimental studies we will disrupt the near-wall autogeneration mechanism, using the SLIPPS actuators, and study the downstream response of the LSS. This approach of disrupting/modifying various parts of the TBL separately and studying the response, will certainly clarify open questions in wall-bounded turbulence regarding causality in nonlinear interactions between scalesThe experiments will be integrated with analytical and simulation studies using Restricted Nonlinear (RNL) models, which have been shown to produce self-sustaining turbulence with accurate structural features. A key feature of RNL models is that they capture the spatio-temporal evolution of a turbulent flow field as it is affected by the control action. They therefore provide benefits over statistical models and approaches analyzing perturbations about a particular mean flow (i.e. resolvent analysis), e.g. they can uncover important mechanisms that would be missed by examining only the pre and post control flow states. The models will be parametrized based on a small set of experiments and then the simplified setting will be exploited to isolate critical information about the non-linear interactions between various structures inside the TBL. The computational tractability of the RNL system will enable us to perform a parametric study of theactuation in order to identify the most promising configurations for further experimental study. The models will also be used to identify the most promising set-ups for experimental studies of closed-loop control strategies using on- and off-the-wall sensors. We believe that the proposed set of complementary experimental and model based studies provide significant advantages overstudies that rely on either simulations or experiments alone.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 26, 2018
- Source ID
- N000141812534
Entities
People
- Stanislav Gordeyev
Organizations
- Office of Naval Research
- United States Navy
- University of Notre Dame