TURBO FAN AND JET ENGINES Flashcards
THE FORWARD FAN DESIGN ON A TURBO FAN ENGINE CAN PRODUCE BETWEEN _____ TO ____ PERCENT OF THE TOTAL THRUST (DEPENDING ON SIZE OF FAN)
THE GAS GENERATOR EXHAUST GAS WILL PROVID THE REMAINING THRUST WICH IS BETWEE ____ AND ____ PERCENT.
30 TO 60
40 AND 70
On a forward-fan design, the fan blades look similar to rotor blades of the compressor that have been enlarged. The cross section of these fans are larger than the front area of the compressor. This allows a relatively large mass of air to bypass the gas generator. On average. this large mass of bypassed air can produce between
30 to 60 percent of the total thrust of a turbofan engine. Some engines have been designed with an even greater amount of thrust from the fans. These percentages depend upon the size of the fan, the turbine arrangements, and atmospheric conditions. Since the fans provide 30- 60 percent of the total thrust. the gas generator exhaust gases will provide the remaining thrust. which is between 40 and 70 percent of that total thrust.
The gas generator turbine section will extract __ percent of the total energy that leaves the burner section just to turn the compressor and accessories. The remaining____ percent will be used for thrust. Part of the___ percent will be converted to mechanical energy through the turbines to drive the fans. The other part will exit the exhaust section as kinetic energy.
75
25
25
These fans push a large mass of ___ which increases _____(T=ma).
air
thrust
Combined with the exhaust gases of the gas generator, the overall thrust is greater than the thrust of a turbojet at the same fuel consumption rate. Thus, to produce the same amount of thrust, the turbofan engine requires less fuel than a turbojet engine and therefore, the turbofan has a lower TSFC.
TURBO FAN REQUIRES LESS FUEL FOR THE SAME AMOUNT OF THRUST THAN A TURBO JET ENGINE.
One of the primary design goals of today’s engines is to maximize the bypass ratio while meeting mission requirements. The most fuel-efficient engines are those with the______ bypass ratio.
higher
Compared to the turbojet, the turbofan is quieter because of the generated thrust from the fans and not just burner combustion. Although performance is high, all turbofan engines are limited at high-end airspeeds and altitudes when compared to the turbojet.
TURBO FANS ARE QUIETER BECAUS OF GENERATED THRUST FROM THE FANS AND NOT JUST BURNER COMBUSTION.
The reduction of the high-end airspeed is due to the large mass of airflow from the fans that is accelerated to only moderate speeds. On a high bypass turbofan engine, more air is bypassed and therefore less thrust comes from the high velocity gases of the gas generator. The altitude limitation is from the lower density air at the high altitudes and therefore, a smaller mass of air is accelerated by the fans.
TURBO FANS FLY SLOWER.
TURBO FAN
ADVANTAGES
DISADVANTAGES
Advantages 1. Higher thrust at low airspeeds 2. Lower TSFC (FUEL BURN) 3. Shorter takeoff distance 4. Considerable noise reduction, 10 to 20 percent over the turbojet Disadvantages 1. Higher specific weight 2. Larger frontal area 3. Inefficient at higher altitudes
- What does the term “gas generator” mean?
- An engine which is operated by converting the energy of expanding gases into propulsive force.
- How is a turbojet constructed?
- Inlet, compressor, burner, turbine, exhaust nozzle.
- How does a turbojet produce thrust?
- By greatly accelerating a small mass of air and expanding the gases leaving the exhaust nozzle.
- What are the advantages and disadvantages of the turbojet?
- Best high speed and high altitude performance. Highest TSFC. Longest takeoff rolls.
- How is a turbofan constructed?
- Fan, compressor, burner, turbine, exhaust nozzle.
- How does a turbofan produce thrust?
- Fan pushes a large mass of air and provides 30-60% of the total thrust.
- How much thrust is produced by the fan on a turbofan? Gas Generator?
- 30-60% from the fan.
40-70% from the gas generator exhaust gases.
- What is meant by “bypass air?”
- Airflow from the fan “bypassed around the gas generator.”
- What are the advantages and disadvantages of the turbofan?
- ADV
- Better TSFC than a turbojet,
- shorter take off distance,
- can lift larger weights.
DIS ADV
1 Large frontal area, - slower, and
- can not fly as high as turbojet.
The gas turbine is an internal combustion engine that uses air as the working fluid. The engine extracts ________ energy from fuel and converts it to_______ energy using the gaseous energy of the working fluid (air) to drive the engine and propeller, which, in turn, propel the airplane.
chemical
mechanical
________ energy from fuel as it is burned is converted to ________ energy in the form of high temperatures and high velocity as the air passes through the combustor. The gaseous energy is converted back to_______ energy in the turbine, providing power to drive the compressor and the output shaft.
Chemical
gaseous
mechanical
The efficiency of the turbine is determined by how well it extracts ______ energy from the hot, high-velocity _______.
MECHANICAL
gasses
The factors that affect the thrust of a gas turbine engine include:
The factors that affect the thrust of a gas turbine engine include:
Air Density
Airspeed
Ram Effect
Engine RPM
Density– Is the mass of a a substance per unit of its volume.
According to the thrust equation:
If mass of airflow increases___________.
If density of air increases- mass will increase and therefore ____________.
- thrust increases
thrust will increase