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Control of turbulent friction force

Periodic Reporting for period 1 - CTFF (Control of turbulent friction force)

Reporting period: 2017-12-01 to 2019-11-30

1.To develop novel active control strategies for the reduction of turbulent friction force.
Active control strategies have been developed via sensitivity calculations as planned and applied to a cylinder flow. This work stems from the collaboration between UoN and ZJU/JHU and has been submitted for journal publications.

2. To evaluate effects of new materials in the passive control of TFF.
New icephobic texture has been designed and tested. This is a collaborative work between UoN and BUAA and has been submitted to a journal for publication.

3.To quantify effects of wall thermal conditions on the dynamics and control of near-wall turbulent structures.
A multi-scale solver to evaluate the wall thermal conditions has been developed. There are 3 secondments for 3 months between UOXF, XJTU and ZJU.

13 journal papers were published / submitted.

Two conferences, two workshops and two summer schools are organized.

A special issue on “Applied Thermal Engineering” is under preparation.

We will ensure that for the following papers, the grant will be properly acknowledged and the paper will be open access.
1. optimal control

Algorithms of the control were derived and implemented in the code and were applied to test cases including both boundary layer flow and cylinder flow.

Particular attention was paid to the surface condition, such as drag reduction on oscillating bodies. A resonance frequency at which free-stream disturbance is greatly amplified was found at such oscillating conditions.

Reduced-order model of the evolution of free-stream disturbance was further developed, aiming at generating signal for control systems based on remote sensing. This has been tested in flow around a flat plate.

Other forms of drag reduction control were also tested including plasma-based actuation, flexible filaments, polymer materials, etc.

2. fluid & heat transfer

The interaction of fluid flow and heat transfer in a nanoscale pipe was thoroughly studied. An analytical solution was obtained and it is further validated by molecular dynamics simulations.

Drag reduction in lubricated pipe flow with a slip boundary condition and a sudden contraction was also studied and the results have been submitted for journal publication.

Coupled solver for fluid and heat transfer was developed for simulations in turbomachinery. It was observed that the heat transfer has limited influence to the fluid flow, which, however, imposes significant feedback to the heat transfer.

4. surface texture.

Experimental study was performed to design supericephobic surfaces in joint projects. This has been submitted for journal submission.

Various surfaces, such as superhydrophobic, deformable, permeable, etc, have been numerically modelled and simulated to find their drag reduction potentials.
The progress listed above are all those beyond the state of the art and are either under consideration of publication or just published.

Expected results and impacts:

1. The nonlinear optimal control acting on a boundary layer that is computed over a sufficiently long time beyond the current limit due to the divergence of the adjoint method.

This will enable real optimal control in vehicles, a revolution of the control actuation and systems.

2. Drag reduction by plasma actuation, combining micro-scale plasma simulation, mesoscale fluid simulation and fluid experiments.

This research will integrate and validate a large number of previous studies and clarify the challenges for the future development of plasma actuations.

3. The mechanism or possibility of joint control of drag and heat transfer in turbomachinery.

The work has significant impacts to engine design since the previous rule is to design the aerodynamic geometry and test the heat transfer afterwards without considering the coupling at the original design stage.
boundary layer flow perturbed by optimal inflow disturbance