Topic of the Day: Turbine Concepts
The information below will help you answer some of the questions asked about turbine engines. Pay attention to the question and read it carefully. Look at the graphic and understand the info. Some questions asked:
At what point does airflow begin to accelerate in a turbine engine? Where is the airflows greatest acceleration?
What happens to pressure at the diffuser?
Which part of a turbine engine is the hottest?
THRUST
Thrust that a gas turbine engine develops is essentially the result of many pressure, temperature and velocity changes as airflow passes through an engine. The figure is a graphical representation of what will typically happen to these properties of airflow within a turbojet engine. The concepts behind thrust production with a turbojet engine will be easily applied to other gas turbine engines.
Gross thrust is a measurement of thrust due solely from the velocity of the exhaust gases. Gross thrust will be produced by a stationary engine; perhaps while mounted on a test stand, or on an aircraft while completing a ‘ground run-up’. This measurement ignores the velocity of the air at the inlet. In addition, the test must have standard conditions or parameters that serve as a baseline to ensure consistent measurements. These conditions include atmospheric pressures and temperatures. Therefore, engineers or maintenance personnel use standard day (29.92″ hg and 15C at sea level) as their baseline for measuring gross thrust. When an engine manufacturer provides the thrust rating of an engine, it is typically the amount of gross thrust it produces. It is often used to compare the thrust produced to another.
Under normal flight conditions, an aircraft engine will seldom be stationary. The measurement of inlet airflow velocity must be included for the calculation of this thrust. Thrust that corrects for the effect of inlet airflow velocity is known as net thrust . The equation for net thrust is simply the thrust equation:
Net thrust and gross thrust will be
equal when inlet airflow velocity is zero
and the atmospheric conditions are
standard. Because net thrust is a more
realistic measurement of an engine’s thrust, the terms thrust and net thrust are often used interchangeably. Therefore, for the remainder of this course, thrust will always be referred to as net thrust.
Thrust that a gas turbine engine develops is essentially the result of many pressure, temperature and velocity changes as airflow passes through an engine. The figure is a graphical representation of what will typically happen to these properties of airflow within a turbojet engine. The concepts behind thrust production with a turbojet engine will be easily applied to other gas turbine engines.
Gross thrust is a measurement of thrust due solely from the velocity of the exhaust gases. Gross thrust will be produced by a stationary engine; perhaps while mounted on a test stand, or on an aircraft while completing a ‘ground run-up’. This measurement ignores the velocity of the air at the inlet. In addition, the test must have standard conditions or parameters that serve as a baseline to ensure consistent measurements. These conditions include atmospheric pressures and temperatures. Therefore, engineers or maintenance personnel use standard day (29.92″ hg and 15C at sea level) as their baseline for measuring gross thrust. When an engine manufacturer provides the thrust rating of an engine, it is typically the amount of gross thrust it produces. It is often used to compare the thrust produced to another.
Under normal flight conditions, an aircraft engine will seldom be stationary. The measurement of inlet airflow velocity must be included for the calculation of this thrust. Thrust that corrects for the effect of inlet airflow velocity is known as net thrust . The equation for net thrust is simply the thrust equation:
Net thrust and gross thrust will be
equal when inlet airflow velocity is zero
and the atmospheric conditions are
standard. Because net thrust is a more
realistic measurement of an engine’s thrust, the terms thrust and net thrust are often used interchangeably. Therefore, for the remainder of this course, thrust will always be referred to as net thrust.
