Numeracal simulation of gas flow in a "stage-diffuser" system in a wide range of modes with experimental verification

Usually at the design stage of a gas turbine the nominal operating mode is considered. This mode is defined by the axial exit of the flow from the turbine, in order to reduce losses with the exhaust velocity. Axial entry into the diffuser is optimal, due to absence of attack angles on the power struts. Struts are the integral part of the diffuser, where the rear bearing support of the turbine rotor is located.
However, gas turbine operates for a long time both in nominal and in variable modes. Partial modes are characterized by significant attack angles on the struts, which leads to flow separation and notable increase in pressure losses in the diffuser. Maintaining a satisfactory flow in the diffuser in the wide range of modes is an important issue.
In this investigation the stage-diffuser system was studied by experimental and numerical methods at wide range of modes. Study has shown that at the last stage flow angle less than 50 degrees, the flow in the diffuser acquires an asymmetric character with developed vortices. This means that numerical simulation in an engineering approach cannot repeat the nature of the flow at low load modes. Nevertheless, a comparison of the experiment and simulation total parameters shows good agreement (a difference of about 5%) even for modes with large attack angles on the diffuser struts.