Analysis of the Exit Flow Angle and Characteristics of Flow in Axial Turbine Cascades

Despite a wealth sophisticated CFD-methods, most designs are still based on one dimensional and two dimensional inviscid computational tools. In such methods realistic loss and angle assessment are absolutely critical in order to arrive at correct loading, flow coefficient and reaction. The selected values are normally kept through the detailed design sequence for each iteration. This means that the throat sizing and the gauge angle is largely based on the early design work.

In a previous publication, formulas were obtained to assess the exit flow in a blade row by Mamaev [2000] in Russian nomenclature and coordinate system. The approach provided by Mamaev offers a unified, seamless and flow-physics based approach for assessing exit angles from e.g. the geometry (gauge angle, uncovered turning, ...), exit Mach number, etc . Analysis of those formulas showed good agreement with physical flow pattern in real cascades for sub-, trans- and supersonic blade profiles.

In this work, the same basic principal procedure is followed by employing the international agreed nomenclature of blades.

The one-dimensional analysis results are validated through fine three dimensional CFD computations for the subsonic and supersonic cascades at varying Mach numbers and flow situations. A mesh convergence study is done for each cascade to make sure that the results are independent of the grid.