Question

Please answer the following questions descriptively: (a) What is a free turbine or power turbine? (b) What is the advantage of using a free turbine? (c) Why does the free turbine driving the propeller and the main turbine driving the compressor rotate in an opposite direction in turboshaft engines? (d) Draw the streamline flow pattern of an external acceleration for subsonic inlet. (e) Draw the streamline flow pattern of an external deceleration for subsonic inlet.

Answer 1

Answer:

a. Free or power turbine

Free or power turbine is the arrangement in which a turbine or the stage of turbine, in the engine of gas turbine do not run the compressor. These types of turbines are used to drive the reduction gears of the propeller in case of the turboprop engine.

In free turbine the power is extracted for the exhaust stream of the gas turbine and this is done with the help of an independent turbine.The turbine which is used is not connected to gas turbine. There us exhaust air which I'd flowing and these airflow spins the turbine which is connected to shaft that's why this setup is termed as free.

(b)Advantges of using free turbine

There are various advantages of using free turbine over fixed turbines and these advantages are as given below and the free turbines are much better than the fixed ones

• The engine and propeller control is very good. in case of free turbines as in fixed turbines the compressor of engine and the turbine has to run at the constant rpm for keeping the propeller from constant so it makes it less efficient as compressor is bound to run at the same speed and it is not allowed to run at the speed at which it can give maximum efficiency. So in fixed turbine engine and propeller control is not that good
• In the free turbines, the propeller is used as a seperate entity so that it reduces the overall amount of torque which is required to start the engine and also reduces the load on the starter motor. Because of this propellers remains feathered when put on shutdown
• Free turbines can be fixed with the brakes. With this type hot section of the engined can be allowed to run while the free turbine and propellers remains stationary. By this engine to power systems can be takes up without even run the propeller

(C)

Free turbine driving the propeller and the main turbine driving the compressor rotates in the opposite direction as like in fixed turbine, the free turbine do not have to run at constant rpm and also free turbines have two independent counter rotating turbine out of which one rotates the propeller and one rotates the compressor. By rotation in the opposite direction, the overall moment of inertia also decreases.

(D) stream line flow pattern of an external acceleration

ca) (0) (2) Aat Streamlines acceleration for

(e) Streamline flow pattern for external deceleration

(1) 7 (2) (9) A a streamlines for Deacceleration