Influence of Peripheral Opening on the Central Core Flow Behaviour in a Rotor-Stator System

International audienceThis work relates to an experimental, theoretical and numerical study of a turbulent flow with separated boundary layers between a rotating disc (rotor) and a stationary one (stator) without any superposed radial flow. The originality of this study is that the pre-swirl ratio at the periphery of the cavity (Kp) is lower than the core swirl ratio (KB) corresponding to the solid body rotation, as predicted by Batchelor in the case of infinite discs: this is what the authors call a rotor-stator system with low pre-swirl ratio. Under these conditions, recent works have shown that the core swirl ratio (K) is a decreasing function of the radius, at least in the peripheral region. This behaviour has rather been observed in the cavities with superposed centripetal radial flow. In the present paper, this flow property is explained starting from an asymptotic approach which leads to step-by-step analytical computation method of the radial distribution of the core swirl ratio (K) and of the static pressure on the stator side p*. The validation of the theory is based both on experimental and numerical results. The experimental tests are carried out in a rotor-stator cavity for different values of the pre-swirl ratio, which is done by geometrical changes of the periphery of the system. The experimental data mostly include the velocity measurements and the turbulent correlations by hot-wire anemometry in interstice between the discs, as well as the static pressure measurements on the stator side. Comparisons with predictions from the CFD code Fluent are also provided. The numerical simulations are performed using the two-equation k – ω SST turbulence model, assuming a 2D-axisymmetric steady flow, in a domain corresponding to the inter-disks spacing and the peripheral outer region of the cavity. Computed and experimental values are in good agreement with the theoretical results