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The present paper introduces a new concept for passive turbine tip-leakage control.The basic idea of the methodis the connection of the blade leading edge and the blade tip by an internal channel.Due to the difference betweenthe stagnation pressure at the leading edge and the low pressure at the blade tip,a small amount of the workingfluid is extracted from the blade passage.At the blade tip,a jet is injected roughly perpendicular to the tip gapflow driven by the blade pressure difference.It is proposed that the jet blocks at least a part of the tip gap flow.Since the tip-leakage losses are proportional to the tip gap mass flow rate,the tip injection results in a reductionof the associated losses.After the introduction of the concept,an analytical model is presented which describesthe reduction of the tip gap discharge coefficient due to the tip injection.Furthermore,the analytical model issupported by the results of a preliminary CFD analysis.Finally,the potential of the efficiency improvement by thepassive blade tip injection method is reported.
The present paper introduces a new concept for passive turbine tip-leakage control. The basic idea of the methodis the connection of the blade leading edge and the blade tip by an internal channel. Due to the difference betweenthe stagnation pressure at the leading edge and the low pressure at the blade tip, a small amount of the working fluid is extracted from the blade passage. At the blade tip, a jet is injected substantially perpendicular to the tip gap flow driven by the blade pressure difference. It is proposed that the jet blocks at a part of the tip gap flow. Since the tip-leakage losses are proportional to the tip gap mass flow rate, the tip injection results in a reduction of the associated losses. After the introduction of the concept, an analytical model is presented which describesthe reduction of the tip gap discharge coefficient due to the tip injection. Still more, the analytical model issupported by the results of a preliminary CFD analysis. Finally, the potential of the efficiency im provement by thepassive blade tip injection method is reported.