Definitive Contract 80NSSC19C0062

THE PROPOSAL FOR THE PHASE II EXTENSION IS TO ADDRESS A SIGNIFICANT ISSUE THAT AROSE DURING THE PHASE II WORK. SIC/SIC CMC MATERIALS HAVE STRENGTH VERSUS TEMPERATURE CHARACTERISTICS DIFFERENT FROM CONVENTIONAL METALLIC HPT TURBINE BLADE MATERIALS. IT IS NOT FEASIBLE TO COOL SIC/SIC CMC BLADES IN ORDER TO ACHIEVE STRENGTHS SIGNIFICANTLY HIGHER THAN THEIR STRENGTH AT THEIR UPPER USE TEMPERATURE. SIC/SIC CMC BLADES HAVE HIGHER TEMPERATURE CAPABILITY THAN CONVENTIONAL METALLIC BLADES, AND BOTH MATERIALS HAVE NEARLY EQUAL STRENGTHS AT THEIR RESPECTIVE UPPER USE TEMPERATURES. AT TEMPERATURES BELOW THEIR UPPER USE TEMPERATURES THE STRENGTH INCREASE AS TEMPERATURE DECREASES IS MUCH LESS FOR SIC/SIC CMC MATERIALS THAN FOR CONVENTIONAL METALLIC BLADE MATERIALS. THE CONSEQUENCE OF THESE DIFFERENT STRENGTH VERSUS TEMPERATURE RELATIONSHIPS IS THAT THE STRENGTH OF A SECOND STAGE SIC/SIC BLADE DETERMINES THE HIGH PRESSURE SHAFT RPM. REDUCING THE HIGH PRESSURE SHAFT RPM INCREASES ENGINE WEIGHT. THE PROPOSED WORK IS TO EXAMINE TWO APPROACHES TO REDUCE HPT BLADE STRESSES, WITHOUT INCURRING A SIGNIFICANT REDUCTION IN STAGE EFFICIENCY. THE FIRST APPROACH IS TO INCREASE BLADE THROUGH FLOW VELOCITY, WHICH REDUCES THE ANNULUS FLOW AREA. REDUCING THE ANNULUS FLOW AREA REDUCES CENTRIFUGAL STRESSES. THE SECOND APPROACH IS TO ANALYZE HIGHLY TAPERED ROTOR BLADES. TAPERING BLADES TO REDUCE THE TIP-TO-HUB AXIAL CHORD RATIO ALSO REDUCES CENTRIFUGAL STRESSES. BOTH STRUCTURAL AND CFD BLADE ROW EFFICIENCY ANALYSES ARE NEEDED. THE TWO APPROACHES ARE NOT EXCLUSIVE, AND MAY BE COMBINED TO ACHIEVE AN OPTIMUM SIC/SIC BLADE CONFIGURATION. WHILE THE FOCUS OF THE WORK IS THE SECOND STAGE BLADE, THE RESULTS ARE APPLICABLE TO THE FIRST STAGE BLADE. WHEN STATOR AND ROTOR BLADES OF BOTH HPT STAGES ARE SIC/SIC BLADES THE MAXIMUM FUEL BURN BENEFIT FROM USING CMC IS ACHIEVED. THE PROPOSED WORK SEEKS TO REDUCE OR ELIMINATE THE CONSTRAINTS IMPOSED ON THE HIGH PRESSURE COMPONENTS BY THE SECOND STAGE BLADE. THE CONSTRAINTS ARE DUE TO THE STRENGTH VERSUS TEMPERATURE CHARACTERISTICS OF SIC/SIC MATERIALS. THE PROPOSED WORK FURTHERS NASA S GOAL OF REDUCED FUEL BURN FOR AIRCRAFT ENGINES. THE NOMINAL N+3 SINGLE AISLE AIRCRAFT ENGINE HAS A TWO STAGE HPT WITH AN OVERALL PRESSURE RATIO OF FOUR. A TOTAL-TO-TOTAL PRESSURE RATIO OF TWO PER STAGE ALLOWS A RELATIVELY HIGH AXIAL MACH NUMBER BEFORE SONIC CONDITIONS ARE REACHED IN EITHER THE STATOR OR ROTOR. PRELIMINARY ANALYSES SHOW THAT SIGNIFICANT STRESS REDUCTIONS CAN BE ACHIEVED FOR EITHER APPROACH WITHOUT A LARGE STAGE AERODYNAMIC EFFICIENCY PENALTY. THE PHASE II WORK SHOWED THAT A 20% REDUCTION IN HP SHAFT SPEED FROM THE N+3 NOTIONAL SHAFT SPEED WAS REQUIRED TO ACHIEVE ACCEPTABLE SIC/SIC CMC BLADE STRESSES. PRELIMINARY ANALYSES INDICATE THAT ACCEPTABLE BLADE STRESSES CAN BE ACHIEVED AT THE N+3 NOTIONAL HP SHAFT SPEED WITH HIGHER THROUGH FLOW AND TAPERED ROTOR BLADES. IN SUMMARY THE PROPOSED WORK IS TO PERFORM STRUCTURAL AND CFD ANALYSES FOR FOUR TURBINE BLADE CON- FIGURATIONS. THESE ARE TWO HIGH THROUGH FLOW CONFIGURATIONS, A TAPERED BLADE CONFIGURATION, AND A COMBINED HIGH THROUGH FLOW PLUS TAPERED BLADE CONFIGURATION. THE REFERENCE CASES FOR THESE ANALYSES HAVE BEEN AN- ALYZED AS PART OF THE PHASE II WORK. FOR THE HIGH THROUGH FLOW CASES STRUCTURAL AND CFD ANALYSES WILL BE DONE FOR BOTH SHROUDED AND UNSHROUDED BLADES. THE EFFICIENCY GAIN DUE TO SHROUDING INCREASES AS THE THROUGH FLOW VELOCITY INCREASES. INCREASING THROUGH FLOW VELOCITY DECREASES ANNULUS HEIGHT AND INCREASES THE CLEARANCE-TO-SPAN RATIO. A HIGHLY TAPERED BLADE IS NOT EXPECTED TO PROVIDE SUFFICIENT STRUCTURAL SUPPORT FOR A SHROUD. FOR EACH CASE THE RESULTS WILL SHOW THE BENEFIT IN TERMS OF REDUCED STRESSES AND THE CHANGE IN STAGE EFFICIENCY.