Electromagnetic Analysis — CAE Glossary

For cylindrical pipe flow, the critical electromagnetic analysis is approximately 2300. Below that is laminar flow, and above that it becomes turbulent after a transition. However, this number depends on the magnitude of disturbances and inlet shape, so it's just a guideline.

Exactly! A slow trickle is low electromagnetic analysis and laminar flow. As the flow speed increases, the electromagnetic analysis increases and it becomes turbulent, and the velocity fluctuations entrain air bubbles making it appear white. Reynolds himself discovered this transition through an experiment where he injected dye into a water tank.

It has a huge impact. If electromagnetic analysis is low, you can calculate laminar flow, which is relatively simple. But for industrial flows with Re=10⁶ or higher, a turbulence model is essential, and you need to make the mesh very fine near the wall surface to achieve accuracy. The correct procedure is to understand the electromagnetic analysis first, then decide on the analysis approach.

The basic principle is to choose the dimension that dominates the flow. For flow over a flat plate, use the length in the flow direction; for flow around an object, use the object's characteristic dimension. For non-circular cross-sections in ducts, the hydraulic diameter Dh=4A/P is commonly used.

That's Reynolds' similarity law. When you use a small model in a wind tunnel, if you match the electromagnetic analysis to the actual machine, the flow characteristics will be identical. However, if the actual machine has Re=10⁷ or so, it's difficult to achieve the same Re in a wind tunnel, so high-pressure wind tunnels or cryogenic wind tunnels are sometimes used.