L13-14 - Turbines Flashcards
Why does the area increase in a turbine?
Becasue the temp and pressure decrease, so dpes the density, and so to keep flow velocity low the area must increase.
What does a turboine stage consist of?
A stage and then a rotor.
What provides power?
The change in whirl velocity?
How large is the change in whirl velcity in a turbine compared to a compressor?
Much larger.
How hot do combustion gases reach?
1750-2000K
What drastically effects the lifespan of turbine blades?
Creep, combination of stress and temperature
What are the three types of turbine blades, crytal wise?
Equiaxed - roughly even crystal sizes throughout, good mechanical properties in all directions.
Directional solidication - Elongated crystals with great longtiudinal strength.
Single crystal - Excellent mechanical properties and temlerature resistance due to no creep.
What is the Reynolds analogy?
Links coeffient of skin friction to heat transfer.
Does laminar or turbulent flow have higher heat transfer?
Turbulent flow increases heat transfer. Thefore ideally the gas flow in laminar and the cooling flows are turbulent.
What are the cooling requirements for Nozzle guide vanes?
These see higher temps than rotor blades, and lower stress. Will suffer oxidation if not cooled properly.
What are the cooling requirements for rotor blades?
Slightly cooler however high stress presenting creep as an issue.
What are the two types of cooling options?
Internal cooling
Barrier Cooling
What are the typed of internal cooling?
Impingement cooling - Tubes of high pressure air blowing on inside of blade.
Passage cooling - Cool air path inside blade
What is the type of barrier coating most commonly used?
Film cooling, blowing cold out out of the blade to create a cooler boundary layer.
What order is the cooling process achieved?
Internal cooling followed by film cooling as the coolant cannot extract anymore heat from the blade yet is still cooler than the combustion gases.
