Axial turbomachine modelling with a quasi-2-D approach. Application to gas cooled reactor transients

Full text of publication follows: In the frame of the international forum GenIV, CEA has selected two innovative concepts of High Temperature gas cooled Reactor. The first has a fast neutron spectrum, a robust refractory fuel and a direct cycle conversion. The second is a very high temperature reactor with a thermal neutron spectrum. Both concepts make use of technology derived from High Temperature Gas Reactor. Thermal hydraulic performances are a key issue for the design. For transient conditions and decay heat removal situations, the thermal hydraulic performance must remain as high as possible. In this context, all the transient situations, the incidental and accidental scenarios must be evaluated by a validated system code able to correctly describe, in particular, the thermal-hydraulics of the whole plant. With this type of reactor a special emphasis must be laid on turbomachinery modelling. A first step was to compute a HTGR concept using the steady-state characteristics of each element of the turbomachinery with the computer code CATHARE. In a hypothetical transient event (a 10 inches cold duct break of primary loop which causes a rapid depressurization and a decrease of the core mass flow rate) the results seem of great interest (as a forced convection was maintained by the compressors during the entire transient) but not sufficiently justified in the frame of 0D modelling of turbomachinery. A more precise description of the turbomachinery has been developed based on a quasi-two dimensional approach. Although this type of flow analysis is a simplification of a complex three dimensional system, it is able to describe the behaviour of a compressor or a turbine with a better understanding than the models based on component characteristics. This approach consists in the solving of 2D radially averaged Navier-Stokes equations with the hypothesis of circumferentially uniform flow. The assumption of quasi-steady behaviour is made: source terms for the lift and drag of each blade cascade of each row are derived from steady correlations. The model is tested on open literature cases of the gas turbine aircraft community: steady and nonsteady (surge cycles). (authors)