Next, looking at the container where the blades are at the base in the center, the whole body of water is spinning well. In this case, as the container starts spinning, the water around the blades starts spinning, then is sent outward by centrifugal force. Supplementing that, the water above that isn't spinning sinks down, meaning the whole body of water can be rotated efficiently. This kind of current is relatively weak compared to the current of the main vortex, so it is called the secondary flow. However, for the vortex, the secondary flow is so important that you could say it decides the fate of the vortex.