Gas Turbine Theory

Two factors are required for proper operation of a gas turbine. One is expressed by Newton’s third law. The other is the convergent-divergent process. Convergent means approaching nearer together, as the inner walls of a tube that is constricted. Divergent means moving away from each other, as the inner walls of a tube that flares outward.

Bernoulli’s principle is used in this process. The venturi of the common automobile carburetor is a common example of Bernoulli’s principle and the convergent-divergent process. The following is a description of a practical demonstration of how a gas turbine operates. A blown-up balloon does nothing until the trapped air is released. The air escaping rearward causes the balloon to move forward (Newton’s
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The hot and rapidly expanding gases are directed aft through the turbine rotor assembly. There thermal and kinetic energy are converted into mechanical energy. The gases are then directed out through the exhaust duct.

Theoretical Cycle of GTE

Let’s discuss a little on the cycle and theory of the gas turbine before we discussion on construction and design. As you are aware, a cycle is a process that begins with certain conditions. This cycle progresses through a series of additional conditions and returns to the original conditions.

The GTE operates on the Brayton Cycle. The Brayton cycle is one where combustion occurs at constant pressure. Various components of the gas turbine were specifically designed to perform individual functions separately. These functions are known as Intake, Compression, Combustion, Expansion, and Exhaust.

The Brayton cycle can also be better explained as air entering the inlet at atmospheric pressure and constant volume. As the air passes through the compressor, it increases in pressure and decreases in volume. Combustion occurs at constant pressure while the increased temperature causes a sharp increase in volume. The gases at constant pressure and increased volume enter the turbine and expand through it. As the gases pass through the turbine rotor, the rotor turns kinetic and thermal energy into mechanical energy. The expanding size of the passages causes further increase in volume and a sharp decrease in pressure. The gases are released through
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The convergent-divergent process is an application of Bernoulli’s principle. (If a fluid flowing through a tube reaches a constriction or narrowing of the tube, the velocity of the fluid flowing through the constriction increases and the pressure decreases. The opposite is true when the fluid leaves the constriction; velocity decreases and pressure increases.) Boyle’s law and Charles’ law also come into play during this process. Boyle’s law: The volume of any dry gas varies inversely with the applied pressure, provided the temperature remains constant. Charles’ law: If the pressure is constant, the volume of dry gas varies directly with the absolute

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