Computer simulations provide a way to see what's otherwise unseeable.
The difficulty has to do with the complexity of the flow. Along with general features that occur over relatively large scales, such as the granulation pattern on the Sun's surface, the researchers need to observe fine details. Very fast time scales and small length scales are involved in this problem. The modeling must also replicate large pressure differentials between the bottom and top of the convection zone. With the CRAY T3D, it became possible to more realistically model this depth differential.