Turbulent Drag Reduction

(Funded by DARPA; joint with Parviz Moin, Sanjiva Lele, and Godfrey Mungal; Mechanical Engineering and the Center for Turbulence Research, Stanford University )

In a broad project that combines all the expertise in the group, we have forged a collaboration with the Center for Turbulence Research to develop a molecular simulation of turbulent drag reduction including the effects of a number of different added micro-elements (e.g. flexible polymers and/or rigid fibers). Note that drag reduction is a 50 year old problem associated with originally with the name Thoms as the Thoms phenomena, where the addition of even very small (i.e. 5 ppm) of polymeric material can cause the reduction of turbulent drag by 80% in fully developed boundary layer and channel flows.

The origins of this reduction at a molecular level are still the subject of heated debate. However, our research using a combination of Brownian dynamics simulations and coupled continuum solver (the so-called micro-macro method) allows for a direct numerical simulation of the phenomena using realistic molecular models that have been benchmarked in our ongoing research program associated with developing Brownian dynamic simulations of model polymers. Note in this context, that we have now developed large scale simulation of drag reduction in external flows, i.e. turbulent boundary layers and demonstrated that polymers both absorb and release energy from the turbulence. The release of energy, at very large levels of drag reduction, is responsible for sustaining the turbulent state itself. An experimental team at Stanford headed by Godfrey Mungal is working with our simulation team to directly examine our flow predictions using 3-dimensional DPIV and direct stress measurements in channel turbulence.

Molecular Simulation of Turbulent Drag Reduction by Flexible Polymers and/or Fibers

 (Funded by DARPA; joint with Parviz Moin, Sanjiva Lele, and Godfrey Mungal;  
 Mechanical Engineering and the Center for Turbulence Research, Stanford University)

In a broad project that combines all the expertise in the group, we have forged a collaboration with the Center for Turbulence Research to develop a molecular simulation of turbulent drag reduction including the effects of a number of different added micro-elements (e.g. flexible polymers and/or rigid fibers). Note that drag reduction is a 50 year old problem associated with originally with the name Thoms as the Thoms phenomena, where the addition of even very small (i.e. 5 ppm) of polymeric material can cause the reduction of turbulent drag by 80% in fully developed boundary layer and channel flows. The origins of this reduction at a molecular level are still the subject of heated debate. However, our research using a combination of Brownian dynamics simulations and coupled continuum solver (the so-called micro-macro method) allows for a direct numerical simulation of the phenomena using realistic molecular models that have been benchmarked in our ongoing research program associated with developing Brownian dynamic simulations of model polymers. Note in this context, that we have now developed large scale simulation of drag reduction in external flows, i.e. turbulent boundary layers and demonstrated that polymers both absorb and release energy from the turbulence. The release of energy, at very large levels of drag reduction, is responsible for sustaining the turbulent state itself. An experimental team at Stanford headed by Godfrey Mungal is working with our simulation team to directly examine our flow predictions using 3-dimensional DPIV and direct stress measurements in channel turbulence.