(latest posts at the top)

09/26/09 Predrag: My first, from the gut answer is

1. please adjust cylinder rotations so they counter-rotate, with zero mean mass flow. Then study carefully regime from Re = 200 to 500, with especiall focus on Re = 400, as we have so many theory results for this particular Reynolds number. The outer rolls should be of width 1, in units of inter-cylinder spacing. For this Re, the 'near-wall' unstable coherent structures are of size 0.5. As long as horizontal rolls are robust (have not flipped into a spiral into axial direction) plane Couette ideas might work.
2. A quick contribution to the currently hot topic of “puffs,” “localized solutions,” “transitions into full spatial turbulance,” etc. would be careful measurements of the transition between locally dying turbulent puffs and onset of spatially sustained turbulence - connects to the current work of Barkley, Tuckerman, Gibson & Schneider, Duguet, etc.. Your [Lx,Ly,Lz] = [230,2,180] cell is just great for that.
3. I am sitting together in a plumbers lab here in Göttingen with at least three Taylor-Couette experts: experimentalists Björn Hof and Kerstin Hochstrate, numerical theorist Marc Avila. They have thought a lot about this system, written proposals, etc.. If it is worth it, Marc is willing to do a calculation in the proposed regime, he has a working Taylor-Couette code. I propose a skype conference (after 3 pm in Merkelandia, 9 am in Obamaland is good).

09/16/09 Daniel Borrero: So we're building a new inner cylinder for our Taylor-Couette apparatus. It is going to be larger so that the ratio of the radius of the inner cylinder to that of the outer cylinder will be 0.95. We are also hoping to have a more subtle perturbation scheme where we don't force the flow globally but instead force it locally with small jets. The idea is to have a series of jets that are positioned along an axial line. Mike wants the spacing between them to be something like the typical spacing between the fast and slow streaks that you see in your simulations. He believes that this will allow us to apply forcing at the same scales and hopefully see some of the structures that you've been seeing in your simulations using the PIV system that we are buying (Yes, the grant was finally approved so hopefully we'll have PIV capabilities come December or so). So I guess the questions that I have for you guys are the following:

1. What is the typical cross-stream spacing (say in units of the gap) between a typical fast streak and it's adjacent slow streak? From the pictures on chaosbook.org/tutorials it seems like it is something like 1 gap width. Do you guys agree with that assessment? Can you provide a better one?

1. Does this spacing change with increasing cell size? Our cell is going to end up being something like [Lx,Ly,Lz] = [230,2,180] (but curved around, of course!), so if the streak spacing varies strongly with system size, we might have to be slightly more careful before we go ahead and build this thing.

1. Do you guys have any other features that you think might be useful? Things that you would like to try and look for?