1. Primary operability risk: compressor surge, stall, blade choking as inlet total temperature and pressure ratio rise; downstream back-pressure transients during bypass/isolation.
2. Flowpath management: bypassing and isolating the compressor using doors/valves, preventing back-flow of hot high-pressure air, scheduling bleeds and variable inlet guide vanes.
3. Thermal environment: inlet total temperatures greater than1000 K cause rapid heating, creep, oxidation, and reduced compressor life; limits time in turbine mode.
4. Controls problem: precise timing of inlet–compressor–ram duct matching; coordination of IGVs, VSVs, bleeds, and splitter/door angles; prevention of inlet unstart during valve motion.
5. Key mechanisms: variable-geometry inlets, splitter/rotor-stator scheduling, high-temperature isolation valves and seals, windmilling considerations during compressor spin-down.
6. Failure signatures: inlet spike motion and unstart, distortion at compressor face, surge margin collapse, transient overspeed or torque spikes.
7. Scheduling: transition typically between Mach 2.5 and 4, when inlet alone can provide sufficient pressure ratio and compressor becomes a drag/thermal liability.
8. Success criterion: smooth unloading of compressor with no surge, stable inlet shock system, minimal total pressure loss, and proper isolation of hot flow.
RBCC (Rocket-Based Combined Cycle) — Ejector to Ramjet/Scramjet Issues
1. Primary operability risk: inlet or isolator unstart, combustor blowout or thermal choking during ejector-to-ram transition; difficulty matching rocket plume with entrained air.
2. Flowpath management: phasing out rocket primaries while maintaining ramjet ignition; controlling ejector entrainment decay; isolator shock train management.
3. Thermal environment: lower turbine-face temperature than TBCC but strong combustion-induced heat release transients in ram/scram combustor.
4. Controls problem: throttling down or shutting off rockets while ensuring stable air capture; staging of fuel injection and ignition; isolator shock-train stabilization.
5. Key mechanisms: rocket primaries, ejector ducts, flameholders, isolators; plasma or piloted ignition aids during low-temperature transitions.
6. Failure signatures: loss of entrainment, isolator pressure rise, buzz, flameout, thermal choking, thrust dip during mode handoff.
7. Scheduling: ejector-to-ramjet transition typically Mach 2–3 , ramjet-to-scramjet transition Mach 5–7 (depends on configuration and fuel).
8. Success criterion: continuous thrust with limited dip, no inlet unstart, clean ignition in ram mode, stable isolator shock train as rocket primaries are phased out.
References (Selected Open Literature)
TBCC:
1. Thomas, S.R., “Overview of the Turbine Based Combined Cycle Discipline,” NASA NTRS, 2009.
2. Saunders, D., “Status of the Combined Cycle Engine Rig,” NASA NTRS, 2009.
3. Csank, J., “A TBCC Engine Inlet Model and Controls Development for Mode Transition,” NASA NTRS, 2012.
4. Garg, S., “Air-Breathing Propulsion Controls and Diagnostics—Transition Testing in NASA Glenn 10×10,” 2015.
Zheng, J., “Modeling and analysis of windmilling operation during TBCC mode transition,” Aerospace Engineering Journal, 2021.
5. Li, Z., “A review on aero-engine inlet–compressor integration and control,” Propulsion and Power Research, 2024.
6. Physics of Fluids, “Impact of splitter rotation speed on mode transition of an over-under TBCC inlet,” 2024.
153 0 0 0
TBCC RBCC Mode switch challenges
Amardip Ghosh #Advanced Propulsion Systems (APSYS) Lab
TBCC vs RBCC Transition Challenges
TBCC (Turbine-Based Combined Cycle) — Compressor-Side Issues
1. Primary operability risk: compressor surge, stall, blade choking as inlet total temperature and pressure ratio rise; downstream back-pressure transients during bypass/isolation.
2. Flowpath management: bypassing and isolating the compressor using doors/valves, preventing back-flow of hot high-pressure air, scheduling bleeds and variable inlet guide vanes.
3. Thermal environment: inlet total temperatures greater than1000 K cause rapid heating, creep, oxidation, and reduced compressor life; limits time in turbine mode.
4. Controls problem: precise timing of inlet–compressor–ram duct matching; coordination of IGVs, VSVs, bleeds, and splitter/door angles; prevention of inlet unstart during valve motion.
5. Key mechanisms: variable-geometry inlets, splitter/rotor-stator scheduling, high-temperature isolation valves and seals, windmilling considerations during compressor spin-down.
6. Failure signatures: inlet spike motion and unstart, distortion at compressor face, surge margin collapse, transient overspeed or torque spikes.
7. Scheduling: transition typically between Mach 2.5 and 4, when inlet alone can provide sufficient pressure ratio and compressor becomes a drag/thermal liability.
8. Success criterion: smooth unloading of compressor with no surge, stable inlet shock system, minimal total pressure loss, and proper isolation of hot flow.
RBCC (Rocket-Based Combined Cycle) — Ejector to Ramjet/Scramjet Issues
1. Primary operability risk: inlet or isolator unstart, combustor blowout or thermal choking during ejector-to-ram transition; difficulty matching rocket plume with entrained air.
2. Flowpath management: phasing out rocket primaries while maintaining ramjet ignition; controlling ejector entrainment decay; isolator shock train management.
3. Thermal environment: lower turbine-face temperature than TBCC but strong combustion-induced heat release transients in ram/scram combustor.
4. Controls problem: throttling down or shutting off rockets while ensuring stable air capture; staging of fuel injection and ignition; isolator shock-train stabilization.
5. Key mechanisms: rocket primaries, ejector ducts, flameholders, isolators; plasma or piloted ignition aids during low-temperature transitions.
6. Failure signatures: loss of entrainment, isolator pressure rise, buzz, flameout, thermal choking, thrust dip during mode handoff.
7. Scheduling: ejector-to-ramjet transition typically Mach 2–3 , ramjet-to-scramjet transition Mach 5–7 (depends on configuration and fuel).
8. Success criterion: continuous thrust with limited dip, no inlet unstart, clean ignition in ram mode, stable isolator shock train as rocket primaries are phased out.
References (Selected Open Literature)
TBCC:
1. Thomas, S.R., “Overview of the Turbine Based Combined Cycle Discipline,” NASA NTRS, 2009.
2. Saunders, D., “Status of the Combined Cycle Engine Rig,” NASA NTRS, 2009.
3. Csank, J., “A TBCC Engine Inlet Model and Controls Development for Mode Transition,” NASA NTRS, 2012.
4. Garg, S., “Air-Breathing Propulsion Controls and Diagnostics—Transition Testing in NASA Glenn 10×10,” 2015.
Zheng, J., “Modeling and analysis of windmilling operation during TBCC mode transition,” Aerospace Engineering Journal, 2021.
5. Li, Z., “A review on aero-engine inlet–compressor integration and control,” Propulsion and Power Research, 2024.
6. Physics of Fluids, “Impact of splitter rotation speed on mode transition of an over-under TBCC inlet,” 2024.
RBCC:
1. Olds, J., “SCCREAM: Simulated Combined-Cycle RBCC Vehicle Model,” AIAA-97-2760.
2. Drummond, J.P., “NATO Overview: RBCC
NASA NTRS Document Link