Turbine Flashcards
How many spools/shafts do modern turbofan engines have, and what is their configuration?
Modern turbofan engines typically have at least two spools/shafts. One connects a low-pressure compressor and turbine, and the other connects a high-pressure compressor and turbine, allowing for efficient operation across different power settings.
What are the primary design goals for turbine engines?
The main goal is to create compression and turbine systems that are as close to isentropic as possible, minimizing heat and stagnation pressure loss through the inlet burner and nozzle, thereby enhancing efficiency and performance.
Why is the ratio of turbine inlet temperature to ambient temperature (τλ = T04/T∞) important in turbine engine performance?
This ratio is crucial as performance improves with higher τλ. Investments in turbine cooling and ceramic coating schemes allow for higher turbine inlet temperatures, significantly boosting engine efficiency and output.
How do parameters like pressure, velocity, and Mach number change across an afterburner, and what strategies enhance thrust when the afterburner is activated?
Across an afterburner, stagnation and static pressures remain nearly constant, and the Mach number stays the same, but velocity increases substantially. Increasing thrust involves burning more fuel, using fuel with higher energy or lower heat capacity.
What are the key considerations in designing a turbine engine for optimal thrust?
Designing for optimal thrust involves considering the relationships between temperature ratios, pressure ratios, operating Mach number, propellant choices, and combustion efficiency. These factors directly influence the engine’s thrust and overall performance.
In what ways is the idealized model of a turbine engine unrealistic?
The idealized model doesn’t account for practical issues like shocks, boundary layer losses, non-adiabatic flow in the inlet and nozzle, or stagnation pressure loss and burner drag in the burner. These factors can significantly affect real-world performance.
What is the purpose of the afterburner?
To increase thrust by injecting additional fuel into the exhaust stream, burning with excess oxygen.
Why are 3-spool engines advantageous in turbojets?
They offer flexible aerodynamic matching, lower inertia, easier starts, and allow for higher ratios of fan airflow to engine flow, improving thrust and fuel efficiency.
What are the characteristics of an idealized turbojet cycle?
It assumes isentropic inlet, diffuser, compressor, turbine, and nozzle processes, with constant pressure combustion and turbine work equal to compressor work.
Describe the losses and inefficiencies in turbojet combustors.
Losses include incomplete combustion, radiation and conduction heat losses to combustor walls, and stagnation pressure loss due to heat addition.
What is the significance of the Adaptive Versatile Engine Technology (ADVENT) program?
It focuses on developing engines with improved efficiency, thrust, and fuel consumption, adaptable to different flight conditions.
