Aircraft Propulsion, 2nd Edition

CHAPTER 10 Aerothermo-dynamics of Gas Turbines

10.1 Introduction

Source: Reproduced with permission from Rolls-Royce plc

Gas turbines produce shaft power for the compressor in the gas generator as well as other external loads, such as the fan in a turbofan, propeller in a turboprop, helicopter rotor in a turboshaft, and electric generator. The high pressure and temperature gas from the combustor enters the gas turbine first through a stationary blade row, known as the nozzle. The first nozzle is thus exposed to the highest gas temperatures in the engine (T_t4 ∼ 1750–2000 K). However, the stationary nature of gas turbine nozzle saves it from an additional centrifugal stress that rotor blades face. Since the gas path temperature is 400–800 K higher than the blade service temperature, all modern gas turbines are cooled. The coolant, which is bled from compressor accounts for ∼10–15% of the airflow rate in the gas generator. A reduction of ∼3% turbine efficiency per 1% cooling flow is attributed to cooling losses. In this chapter, we will introduce aerodynamics of turbine blades, optimal nozzle exit tangential Mach number, optimum solidity, turbine losses, and cooling. We conclude the chapter with axial-flow turbine design and practices and an example. Figure 10.1 shows a schematic drawing of a gas turbine.

FIGURE 10.1 Schematic drawing of an axial-flow turbine

10.2 Axial-Flow ...