Gasturbine Performance Deel 1
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The principle of propulsion by aircraft gas turbines is the increase of the … of the air.

  • density
  • pressure
  • velocity (correct)
  • temperature

    • When is the propulsive efficiency of a jet engine the lowest?

  • At high altitude at maximum velocity and full throttle
  • During idle descent
  • During take-off
  • When doing a test run with zero velocity on the ground (correct)

    • For the calculation of the thrust of an unchoked turbojet, besides the mass flow, we only need the … of the airflow.

  • gear
  • initial velocity
  • terminal velocity
  • velocity increase (correct)

    • What is the most common arrangement of the pistons in a reciprocating engine of a propeller aircraft?

    <p>c</p> Signup and view all the answers

    In a cylinder, we have gas under a free movable piston. On the position is a mass of 5 𝑘𝑔. At some point, I remove the mass of the piston so that the piston moves up VERY slowly. What statement is NOT correct?

    <p>The temperature of the gas increases</p> Signup and view all the answers

    In a petrol engine whose thermodynamics is described by the Otto-cycle, the ignition is:

    Signup and view all the answers

    If we want to increase the efficiency of a reciprocating engine (without changing the dimensions of the piston) then we can do that by:

    <p>compressing the gas in the piston to a smaller volume.</p> Signup and view all the answers

    In a reciprocating engine the compression ratio is:

    <p>𝑉1 𝑉2</p> Signup and view all the answers

    If we increase the RPM of a reciprocating engine and do not change the fuel-air ratio, then the work per second (1) … and the specific work (2) …

    <p>(1) increases (2) stays the same</p> Signup and view all the answers

    A Diesel engine has a (1) … efficiency than a gasoline engine. That is partly because the Diesel has a much (2) … compression ratio than a gasoline engine.

    <p>(1) higher (2) higher</p> Signup and view all the answers

    The (1) … is driven by the (2) …

    <p>(1) compressor (2) turbine</p> Signup and view all the answers

    A turboshaft is used by:

    <p>helicopters</p> Signup and view all the answers

    Which form of energy is included in total enthalpy, but NOT in enthalpy?

    <p>Kinetic energy</p> Signup and view all the answers

    In the inlet of a turbofan the temperature of the airflow (1) … and the total temperature (2) …

    <p>(1) increases (2) stays the same</p> Signup and view all the answers

    What is the form of the First Law, applied to a combustion chamber?

    <p>Δ𝐻0 = 𝑄</p> Signup and view all the answers

    What temperature limits the maximum thrust of the engine?

    <p>T04</p> Signup and view all the answers

    The thermal efficiency of a gas turbine mainly depends on the:

    <p>pressure ratio over the compressor</p> Signup and view all the answers

    The total efficiency is the ratio between the power absorbed by the (1) … and the power released by the (2) …

    <p>(1) aircraft (2) fuel</p> Signup and view all the answers

    The largest fuel-air ratio is needed in a combustion chamber with a (1) … inlet temperature and a (2) … temperature increase.

    <p>(1) high (2) high</p> Signup and view all the answers

    What happens with the critical pressure if we replace the outlet by an outlet with a larger outlet opening? (All other parameters stay the same). The critical pressure:

    <p>stays the same</p> Signup and view all the answers

    If the process in the (1) … is isentropic, the increase of the total temperature of the air is (2) … than when it is adiabatic.

    <p>(1) compressor (2) smaller</p> Signup and view all the answers

    The increase of the TIT has a beneficial effect on:

    <p>the thrust, but not on the TSFC</p> Signup and view all the answers

    (I) When cruise altitude increases the thrust decreases (II) When cruise altitude increases the specific thrust increases

    <p>(I) is right, (II) is right</p> Signup and view all the answers

    By a (1) … airflow through the bypass and a (2) … airflow through the core we know FOR SURE that the BPR decreases.

    <p>(1) smaller (2) larger</p> Signup and view all the answers

    The advantage of a geared turbofan is, that the (1) … can rotate (2) … than the fan.

    <p>(1) LPT (2) faster</p> Signup and view all the answers

    When the … an assumed temperature is determined for the take-off.

    <p>take-off weight is less than the maximum take-off weight</p> Signup and view all the answers

    What is NOT used as an indication of thrust?

    <p>N2</p> Signup and view all the answers

    What parameters determine the propulsive efficiency of a turbofan engine?

    <p>BPR and FPR</p> Signup and view all the answers

    The casing of the compressor converges. This keeps the … of the airflow constant.

    <p>axial velocity</p> Signup and view all the answers

    A drum-type rotor is … compared to a disc-type rotor.

    <p>lighter and more vulnerable</p> Signup and view all the answers

    (I) In the rotor of a compressor, the total temperature increases (II) In the stator of a compressor, the temperature stays the same

    <p>(I) is right, (II) is wrong</p> Signup and view all the answers

    In the compressor the absolute velocity in the rotor (1) … and in the stator (2) …

    <p>(1) increases (2) decreases</p> Signup and view all the answers

    If we want to design a compressor to transfer a maximum amount of power to 1 kg of air, then we need a combination of a (1) … axial velocity of the airflow, a (2) … rotational velocity of the rotor and a (3) … blade curvature.

    <p>(1) high (2) high (3) large</p> Signup and view all the answers

    The (1) … image gives the required compressor blades for a degree of reaction of 1, because the pressure is entirely build-up in the (2) …

    <p>(1) right (2) rotor</p> Signup and view all the answers

    If we do NOT provide the compressor blades with a wrong, and the relative airflow on half the blade height exactly follows the blade shape, then by the (1) … of the blade stall might occur because there the angle 𝛽1 is too (2) …

    <p>(1) tip (2) large</p> Signup and view all the answers

    A compressor consists of a low- and high-pressure compressor. Both the low- and highpressure compressor consist of 8 stages. All stages have a pressure ratio of 1.2. The air enters the compressor with a pressure of 1 bar. The pressure increase in the low-pressure compressor is (1) … bar, and that in the high-pressure compressor (2) … bar.

    <p>(1) 3.30 (2) 10.90</p> Signup and view all the answers

    The picture shows a velocity triangle at which (1) … can occur. This is caused by a too (2) … axial velocity.

    <p>(1) stall (2) low</p> Signup and view all the answers

    If a gas turbine accelerates from 0 to idle the VSVs (1) … and the VBVs (2) …

    <p>(1) open (2) close</p> Signup and view all the answers

    If we compare the stage of a radial compressor with that of an axial compressor, then the radial compressor’s stage has a relatively:

    <p>high pressure ratio</p> Signup and view all the answers

    In an impeller the total temperature (1) … in a diffuser it (2) …

    <p>(1) increases (2) stays the same</p> Signup and view all the answers

    Compared to a turbine blade, a compressor blade has a:

    <p>larger wrong</p> Signup and view all the answers

    In order to expand the gas and get a high gas velocity, the passage between blades of the turbine must be:

    <p>converging</p> Signup and view all the answers

    The velocity triangle at the entrance of the impeller of a centrifugal compressor differs on 1 point with that at the entrance of the rotor of an axial compressor. What?

    <p>𝛼1 = 0</p> Signup and view all the answers

    In an impulse turbine the pressure drop take place:

    <p>completely in the stator</p> Signup and view all the answers

    Study Notes

    Propulsion by Aircraft Gas Turbines

    • The principle of propulsion by aircraft gas turbines is the increase of the air's velocity.

    Jet Engine Efficiency

    • The propulsive efficiency of a jet engine is lowest when the propulsive efficiency is lowest.

    Thrust Calculation

    • For the calculation of the thrust of an unchoked turbojet, the mass flow and the velocity of the airflow are required.

    Reciprocating Engine

    • The most common arrangement of the pistons in a reciprocating engine of a propeller aircraft is inline.

    Piston Movement

    • When the mass of the piston is removed, the piston moves up VERY slowly.

    Otto Cycle

    • In a petrol engine whose thermodynamics is described by the Otto-cycle, the ignition is spark ignition.

    Increasing Efficiency

    • To increase the efficiency of a reciprocating engine, the compression ratio can be increased without changing the dimensions of the piston.

    Compression Ratio

    • In a reciprocating engine, the compression ratio is the ratio of the maximum volume to the minimum volume.

    Work Per Second

    • If the RPM of a reciprocating engine is increased and the fuel-air ratio remains the same, the work per second increases and the specific work decreases.

    Diesel Engine

    • A Diesel engine has a higher efficiency than a gasoline engine due to its higher compression ratio.

    Turboprop

    • The turboprop is driven by the propeller.

    Total Enthalpy

    • The total enthalpy includes kinetic energy, but not potential energy.

    Inlet Temperature

    • In the inlet of a turbofan, the temperature of the airflow decreases, but the total temperature remains the same.

    First Law of Thermodynamics

    • The First Law of Thermodynamics applied to a combustion chamber is ΔE = Q - W.

    Thermal Efficiency

    • The thermal efficiency of a gas turbine mainly depends on the turbine inlet temperature (TIT).

    Total Efficiency

    • The total efficiency is the ratio between the power absorbed by the propeller and the power released by the turbine.

    Fuel-Air Ratio

    • The largest fuel-air ratio is needed in a combustion chamber with a low inlet temperature and a high temperature increase.

    Critical Pressure

    • If the outlet is replaced by an outlet with a larger opening, the critical pressure decreases.

    Isentropic Process

    • If the process in the compressor is isentropic, the increase of the total temperature of the air is less than when it is adiabatic.

    Increase in TIT

    • The increase of the TIT has a beneficial effect on the thermal efficiency.

    Thrust

    • When cruise altitude increases, the thrust decreases, but the specific thrust increases.

    Bypass Ratio

    • If the airflow through the bypass decreases and the airflow through the core increases, the BPR decreases.

    Geared Turbofan

    • The advantage of a geared turbofan is that the turbine can rotate faster than the fan.

    Take-Off

    • An assumed temperature is determined for the take-off.

    Propulsive Efficiency

    • The parameters that determine the propulsive efficiency of a turbofan engine are the fuel-air ratio, specific thrust, and specific work.

    Compressor

    • The casing of the compressor converges to keep the mass flow of the airflow constant.

    Drum-Type Rotor

    • A drum-type rotor is heavier compared to a disc-type rotor.

    Rotor and Stator

    • In the rotor of a compressor, the total temperature increases, and in the stator, the temperature stays the same.

    Axial Velocity

    • In the compressor, the absolute velocity in the rotor decreases, and in the stator, it increases.

    Compressor Design

    • To design a compressor to transfer a maximum amount of power to 1 kg of air, a combination of a low axial velocity, a high rotational velocity, and a high blade curvature is required.

    Blade Stall

    • If the relative airflow on half the blade height does not exactly follow the blade shape, blade stall might occur due to a high angle β1.

    Multi-Stage Compressor

    • A compressor consists of a low- and high-pressure compressor, and the pressure increase in each stage is cumulative.

    Velocity Triangle

    • The velocity triangle at the entrance of the impeller of a centrifugal compressor differs from that of an axial compressor due to the radial velocity component.

    Radial Compressor

    • The radial compressor's stage has a relatively high pressure ratio compared to an axial compressor.

    Impeller and Diffuser

    • In an impeller, the total temperature increases, and in a diffuser, it decreases.

    Turbine Blade

    • Compared to a turbine blade, a compressor blade has a lower camber angle.

    Turbine Passage

    • To expand the gas and get a high gas velocity, the passage between blades of the turbine must be convergent.

    Centrifugal Compressor

    • The velocity triangle at the entrance of the impeller of a centrifugal compressor differs from that of an axial compressor due to the radial velocity component.

    Impulse Turbine

    • In an impulse turbine, the pressure drop takes place in the nozzle.

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    This quiz covers GTP SOCRATIVE 2022-2023 with exam solutions. Test your knowledge and earn extra income with this aviation-focused quiz.

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