Off-Design Considerations through the Properties of Some Pressure-Ratio Line of Radial Inflow Turbines

Abstract EN

Radial turbines are commonly used in applications involving operation through severe off-design conditions.

The emergence of variable-geometry systems leads to the distinction between two off-design concepts: operational and geometric off-designs.

Both of these operating constraints should be integrated in the design procedure.

Recent developments in prediction and optimization methods allowed such an integration, but involving complex algorithms is coupled with semiempiric loss models.

This paper provides a basis to obtain simple information from an existing or predesigned machine, for both operational and geometric off-design conditions.

An alternative turbine map is defined using loading and flow coefficients.

A one-dimensional analysis shows that the constant pressure-ratio lines are straight lines whose slope is remarkably correlated with the pressure-ratio value and geometrical characteristics.

This theoretical approach is validated against the experimentation of two machines, the linearity is observed in both cases.

The direct influence of the stator configuration on the pressure-ratio lines confirms the applicability of this work to variable-geometry stages.

A dimensionless cross-section of the stator is thus defined.

However, the unexpected displacement of the intercept of the pressure-ratio lines limits the application field of this method.

Nevertheless, a simple performance prediction analysis is proposed for blocked mass flow operation.