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[4] The Beltrami flow is defined as a field v_B that satisfies omega_B=nabla v_B = gamma v_B, with gamma = constant. We say that the flow has a beltrami flow structure when it can be put in the form v = U e_z + Omega r e_theta + v_B, being U and Omega constants, i.e it is the superposition of a solid body rotation and traslation with a Beltrami one. For a potential flow gamma = 0.

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