燃气轮机计算分析

ME 423

Chapter 8 PREDICTION OF PERFORMANCE OF SIMPLE GAS TURBINES

Prof. Dr. O. Cahit ERALP

•From cycle calculations it is possible to determine the PRESSURE RATIO ( R c ) which will give the best overall efficiency for a given T max .

•MASS FLOW RATE to give the most suitable desired power output.

•After such preliminary calculations, the most suitable design data for a particular application can be chosen.

•Then, it is possible to design individual components to give the required operation at the design point.

•That is running at the design speed N*, mass flow rate m* and pressure ratio R*.

Prediction of Performance of Simple Gas Turbine

()m

Prediction of Terformance of Simple Gas Turbine •Then the off-design performance has to be determined which is the divergence from the design point over the

complete operating range of speed and power output. •The performance ¢ of the individual components may be estimated on the basis of the previous experience or actual experiments. When they are combined in an engine their operating range is considerably reduced. •The problem is to find the Operating point (OP) on each component ¢when the engine is running at a steady speed (EQUILIBRIUM).

•The plot of these OP's form the EQUILIBRIUM RUNNING LINE (ERL).

Prediction of Performance of Simple Gas Turbine •For the whole range of operating speeds, it will generate the EQUILIBRIUM RUNNING DIAGRAM. •Determining the OP; the power output, thrust and the

SFC can be obtained.

•The Equilibrium Running Diagram indicates the margin of operation from the surge line (SL) .

• This margin indicates a Margin of stability; indicates if there is enough margin to operate with adequate compressor efficiency.

•If the surge line is crossed some action has to be taken to recover, not to give rise to a failure.

•Ideally the engine should be operated within the region of maximum possible efficiencies.

Prediction of Performance of Simple Gas Turbine •Variation of SFC with reduction in power → PART LOAD PERFORMANCE. This is important while running the GT at low power settings.

•Poor sfc at part load is the biggest disadvantage of a GT, especially a vehicular one.

•The effect of ambient conditions on maximum output is also important, i.e. high & low T a and P a.

•Peak load energy generation:

→ Europe: cold days in winter,

→ America: hot days in Summer

→ for airplanes: Runway length (safety) and

pay load (economics) are affected.