Secondary Flow Instabilities
Secondary flows are defined as those flows which have components in a plane orthogonal to the main direction of flow (1). In a two-dimensional representation, these secondary flows appear as vortices or eddies, circulating in a directionopposite to themain (x) flowdirection (seeFig. 3.1a from simulations in entry flow in a contraction, where the flow as seen by velocity vectors is coming from left) (2). In a three-dimensional representation, it is possible that these secondary flows take a helical path traveling also in the third (z) direction (Fig. 3.1b from simulations in entry flow in a contraction) (2).