Figure 3-1O shows a similar performance map for an axial-flow com-pressor. .ote the smaller operational flow range for the axial-flow compres-sor as compared to the centrifugal compressor. Figure 3-11 shows a typicalcompressor map presented from a slightly different viewpoint. On thismap， the constant aerodynamic speed lines are functions of the power and flow rate. Constant pressure lines and efficiency islands are also shown on the same map.
Turbine Performance Characteristics
The two types of turbines一axial-flow and radial-inflow turbines一can be divided further into impulse or reaction type units. Impulse turbines taketheir entire enthalpy drop through the nozzles， while the reaction turbine takes a partial drop through both the nozzles and the impeller blades.
The two conditions that vary the most in a turbine are the inlet pressure and temperature. Two diagrams are needed to show their characteristics. Figure 3-12 is a performance map that shows the effect of turbine inlet temperatureand pressure， while power is dependent on the efficiency oftheunit， the flowrate， and the available energy (turbine inlet temperature). The effect of efficiency with speed is shown in Figure 3-13. Figure 3-13 also shows the difference between an impulse and a 5O% reaction turbine. An impulse turbine is a zero-reaction turbine.
120
100
80
60
40
20
0
0 20 40 60 80 100 120 140 160 Gas Flow (%)
Gas Turbine Performance Computation
The following is a sample computation of the techniques used to deter-mine the performance of a gas turbine. A test was run on a ..E. Frame 5 simple-cycle single-shaft unit as shown in Figure 3-14. The exhaust energyfrom this unit was recovered in a heat recoveryboiler， which with supple-mentary gas firing， delivered 175，OOO lbslhr (79，545 kglhr) of steam at 655 psia
(44.8 Bar) and 75O .F(398 .C). It has a small steam turbine that acts as a starter unit. Figure 3-15 is a schematic of the system. The gas turbine was operated from about 25% load to full load. Full load was determined to be when the turbine"s automatic controls took over. These controls are actuated by the exhaust temperature.
Figure 3-16 shows the effect of efficiency as a function of the load for both the compressor and turbine. Part-load turbine efficiencies are affected more than compressor efficiencies. The discrepancy results from the compressoroperating at a relatively constant inlet temperature， pressure， and pressureratio， while the turbine inlet temperature is greatly varied (Figure 3-17).
1650°F
894°C
1350°F 732°C
1050°F
566°C
0 3,750 7,500 11,250 15,000 load in kWh
The turbine pressure ratio， however， remains relatively constant. The back-pressure on the turbine was measured at a relatively constant value of 3O.25 inches Hg abs (1.O2 Bar). This value creates about a 9-inch H2O (228 mm H2O) back-pressure on the turbine. The efficiency of the compres-sor is based on the following equation:
「「
(，-1)
，
Pt2
Tt1 -1Pt1 Tc -(3-43)
eTact
where:
Tt1 -inlet temperature
Pt2 -pressure at compressor outlet
Pt1 -pressure at compressor inlet
eTact -actual temperature rise in the compressor
， -specific heat ratio; average value between
inlet and outlet temperature was used
The turbine efficiency calculation is more complex. The first part is the calculation of the turbine inlet temperature. The calculation is based on the following equation:
m的 acP2Tt2 +nbm的 j (LHV natural gas)Tt3 -cP3cP3(m的 j +m的 a)(3-44)
where:
Tt2 -temperature at the outlet of the compressor
cP -specific heat at constant pressure
m的 j -mass flow rate for the fuel
m的 a -mass flow rate of the air
Tb -combustion efficiency (LHV)-lower heating value of the natural gas supplied (95O Btu/cu ft [(35，426 kJ /cu m)] and specific gravity O.557) 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：燃气涡轮工程手册 Gas Turbine Engineering Handbook 1(50)
