![]() In their study published in Scientific Reports, the team resorted to an approach called "reinforcement learning" (RL), in which intelligent agents take actions in an environment to maximize the cumulative reward (as opposed to an instantaneous reward). The viscosity at the boundaries makes the fluid stick to the boundary which is why a shear develops within the interior of the fluid.Can an optimized mixing be achieved for laminar flows instead? To answer this question, a team of researchers from Japan, in a new study, turned to machine learning. We assume that the pressure gradient is zero and that the only forcing on the fluid is forcing due to the moving plate. Plane Couette flow is the name given to steady flow between two parallel plates where the bottom plate is stationary while the top plate is moving. Here are some examples: Plane Couette flow This second type of flow is know as turbulent flow.įor some simple cases of laminar flow exact analytical solutions to the Navier-Stokes equations can be computed. On the other hand if the faucet is turned on high the flow pattern becomes very irregular, with chaotic trajectories which are no longer in straight lines. The water comes out in straight lines and the motion is rather smooth. This can be seen when a water faucet is turned on low. Laminar flow has motion that is very regular and predictable. Shear flow can be classified into two different categories: laminar and turbulent. ![]() Turbulentīefore getting into more about laminar flow we need to get a better understanding of what it is. Purcell, American Journal of Physics vol 45, pages 3-11 1977. If you are interested, not in swimming in molasses but in reading more on this topic, I encourage you to read the article " Life at Low Reynolds Number" by E.M. If we wanted to get anywhere we would have to copy these microorganisms. If we ever had to swim through a vat of viscous fluid like molasses our regular swimming techniques wouldn't work. Actually anything that swims slowly in water and is very small will have a small Reynolds number and consequently must swim in a very different manner because viscosity dominates over inertia. In this case the Reynolds number relevant to our zooplankton is 10 -5 and thus viscosity is much more important than inertia for these organisms. Zooplankton can be as small as several microns which means that their length scale is about 10 -6 m, they swim at about 10 -5 m/s and the viscosity coefficient is the same as before. What is the Reynolds number of zooplankton swimming in water? This is why molecular viscosity is not important when we are swimming in water. Therefore our Reynolds number is on the order of 10 6 which is much larger than one. The average swimming velocity for people is on the order of 1 m/s, the length scale is set by the persons height which is on the order of 1 m say and the dynamic viscosity is about 10 -6m 2/s. What is the Reynolds number for a person swimming in water? This ratio is represented by the Reynolds number, Which is nearly constant for water, but rather by the ratio of the viscous term to the inertial (or nonlinear) term. The reason why is that the importance of viscosity within a fluid is not determined by, In our everyday experiences with water it appears to be inviscid, however this is not always the case. Outside of the boundary layer, which is usually where the majority of the fluid lies, viscosity is negligible. ![]() This region where viscosity is important is called a boundary layer. In many fluid dynamical models we are justified in neglecting viscosity since it is only influential in a thin region near solid objects. ![]()
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