T-stage
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- T-stages are the small compressor stages, featured on some turbofan engines, that are mounted on the LP shaft directly behind the fan. Although T-stages usually only supercharge the core stream, some engines do feature a deliberately oversized IP compressor, which compresses both the core flow and a proportion of the bypass flow. This enhances the stability of the T-stages during throttling. Where necessary, the alternative is to employ blow-off valves.
- T-stages are used to increase overall pressure ratio and, for a given core size, the core mass flow. This is demonstrated by the following relationship:
- [w_2 = (w_2 \sqrt/P_3) * (P_3/P_2) * (\sqrt) * (P_2/\sqrt) \,]
- where:
- core mass flow = [w_2 \,]
- core size =[(w_2 \sqrt/P_3) \,]
- core total head pressure ratio = [(P_3/P_2) \,]
- core entry total pressure = [P_2 \,]
- core entry total temperature = [T_2 \,]
- Note:
- in this case, the core refers to the whole of the gas generator compression, not just that of the HP compressor.
- T-stages are a popular method for uprating the thrust of an engine (e.g. Pratt & Whitney Canada PW500).
- The alternative is to place a zero-stage, mounted on the HP shaft, at the front of the HP compressor. This approach implies a significant change in the HP turbine, whereas a T-stage can, if necessary, be accommodated by simply adding an additional stage to the rear of the LP turbine.
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