Create an illustrated explainer poster about vortex shedding behind a cylinder in a flowing fluid. Show a labeled diagram with: incoming flow arrows, boundary layer separation points, alternating vortices in the wake, and a simple Strouhal relation (St = fD/U). Include a small inset comparing laminar vs turbulent flow, and a legend for arrows/streamlines/pressure regions. Style: clean vector infographic, limited palette (navy, teal, coral, off-white), subtle paper grain. Keep all labels short and perfectly legible.