Session: 32-07 Loss Reduction for Axial Turbines

Submission Number: 177173

Separating Turbine Stage Efficiency Effects due to Combined Variations of Cooling Flow and Tip Clearance 

Efficiency losses resulting from blade tip clearance effects have historically challenged turbine designers and tip clearance tolerances are expected to increase in scale with the transition to small core engines along with the associated aerodynamic penalties. However, blade cooling requirements are following an increasing trend as turbine entry temperature increases. Despite this trend, limited research has been done to study the effect of blade cooling flow on stage efficiency. Furthermore, changes in cooling flows induce changes in tip clearance due to thermal growth, creating a combined effect on stage performance. With this in mind, the current study separates the combined effect of cooling flows and tip clearances on stage efficiency. This experimental investigation was completed using the National Experimental Turbine (NExT™) in the Steady Thermal Aero Research Turbine at Penn State University. Macro-scale turbine tip clearance effects were studied by comparing turbine stage efficiency across two builds with different tip clearances, and a magnetic bearing system was used to introduce local, micro-scale adjustments to further quantify tip clearance efficiency sensitivities. General efficiency trends from this study support prior literature showing a one-point efficient increase for each one-percent decrease in tip clearance-to-span ratio; however, this work is the first to study the combined effect of blade cooling flow and tip clearance, showing an inverse linear dependence of blade cooling flow on local sectors of thermal efficiency when tip clearance was maintained constant. Ultimately, this study shows decreases in blade cooling flow cause minimal changes to tip clearance due to thermal growth with efficiency primarily driven by cooling flow. However, large design changes in tip clearance remain as a primary contributor affecting turbine stage efficiency.

Presenting Author: Matthew Stuber The Pennsylvania State University

Presenting Author Biography: Matthew Stuber is a graduate research assistant in the START Lab at the Pennsylvania State University. He is conducting his graduate research under the direction of Dr. Reid Berdanier. His research is primarily focused on turbine aerodynamics and cooled turbine stage efficiency.

Authors:

Matthew Stuber The Pennsylvania State University
Matthew Meier The Pennsylvania State University
Reid Berdanier The Pennsylvania State University