iTurbo vs Navier Stokes Explained

This application performs a Direct Numerical Simulation (DNS) where the Navier-Stokes equations are solved for two dimensional incompressible homogeneous turbulence. These equations are a set of nonlinear partial differential equations. The time stepping is performed with a simple Euler method where the time step is calculated so that the CFL number does not exceeds the given number (should be less than 0.8 otherwise the simulation blows up). The equations are solved in the Fourier space where the calculation of the nonlinear term transforms to a simple multiplication. The main CPU usage is consumed by transforming the vorticity field back and fourth between the Normal space where the time-stepping is performed and the Fourier space where the nonlinear term is calculated.

The Navier-Stokes equations describe how every liquid and gas moves. They are usually met as a wall of symbols. Here they are a tank of water you can hold. A real three-dimensional fluid solver runs on your iPhone's GPU. Drop a column of water, stir a tank, push a flow past a sphere, or turn on Tilt and let gravity follow your phone. Then look inside: color the water by speed, pressure or rotation, tap anywhere to measure it, and open the live values to see each term of the equation as an arrow at that point. In still water the pressure arrow and the gravity arrow cancel, which is what the equation says they must do. FOUR GUIDED LESSONS Predict, watch, compare, explain. • Why does a swirl fade? The same stir in two liquids, 10,000 times apart in viscosity. • What holds water up? Measure pressure at two depths. • How does flow turn? A pulse of water meets a solid sphere. • Why doesn't water squash? The same falling column with pressure switched off. A LAB, NOT A VIDEO • Gravity, viscosity and stirring strength are yours to change, with a live Reynolds number. • Velocity and pressure arrows, tracer trails, pause, single-step and half speed. • Every term of the equation opens a plain-language explanation and an experiment to try. • Works offline. No account.