Study on laminar to turbulent transition in a 90° curved duct is carried out. Professional mesh generation tool ICEM is used to create geometry model and generate mesh, then the mesh is imported to the fluid dynamics software CFX to simulate three-dimensional flow. The dimensionless parameter K is calculated in the duct with velocity and pressure distribution obtained by numerical simulation. According to energy gradient theory, K is the ratio of energy gradient in the transverse direction to that in the streamwise direction, which can be used to measure stability of the flow field. It is found that fluid is most likely to lose its stability where the maximum K is, and laminar to turbulent transition occurs when K reaches a certain value, corresponding to the critical Reynolds number. The instability and transition characteristics predicted by energy gradient method agree well with former researchers’ results.

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