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HOW TO CALCULATE A SINGLE CYCLE

GasTurb 12 – Tutorial 1

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A Jet Engine Example

The Program offers three Scopes that differ in the amount of detail being simulated. The

Basic Thermodynamics

scope is least demanding for the user.

Only simple textbook wisdom is considered.

For professional performance work use the

Engine Design option. Choose Performance

or…

More… if you want to determine the engine

geometry.Let us begin with a jet engine simulation. Select the most

simple engine architecture, a Turbojet.

A click on Performance in the Engine Design button group

begins the calculation

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We Need Some Data…

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Cycle Design Input Data Window

All input is in clear nomenclature - no cryptic abbreviations are

used.

Switching to Imperial Units is easy

Let’s go back to SI Units

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Thermodynamic Station Input

The flow areas at the stations are either a design point input

or are derived from a Mach number. These flow areas

affect only the static pressures and temperatures. The main cycle parameters like thermal

efficiency or thrust, for example are not affected by the input on

the Stations page.

Click here to start the calculation

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Single Cycle Output

On this summary page there is no room for lengthy property names. The international standard nomenclature for performance computer programs is employed. For example, P is total pressure, T total temperature andW is employed for mass flow.

Explanations are at your fingertip: Click a symbol – for example TSFC - and you get a detailed explanation.

Most people are using m for mass flow. When the standard

nomenclature was agreed on the letter M could not be used

because in early FORTRAN programs any property name

beginning with M was an Integer. The letter W for mass flow

reminds of the outdated designationweight flow.

Most people are using m for mass flow. When the standard

nomenclature was agreed on the letter M could not be used

because in early FORTRAN programs any property name

beginning with M was an Integer. The letter W for mass flow

reminds of the outdated designationweight flow.

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Thermodynamic Station Output

Here are all the details at the thermodynamic stations.

The flow areas at all the stations are stored in memory. During off-design simulations the

static pressures and temperatures are calculated from flow area, mass flow, total

pressures and total temperature.

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Getting Additional Output

Open the Composed Values window – a powerful formula

editor.

I need to know a cycle property

which is not listed on the output page.

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Composed Values Editor

Click here to check and evaluate all

composed values.

Compose your additional output values from the input and output quantities. You can even use empirical correlations (Tables) and more than 50 predefined Functions

Example: Calculate the kinetic energy of the nozzle exhaustJetEnergy=W8*V8^2/2Dividing by 1000 yields the Jet Energy in kW

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Output with Composed Value

After closing the Composed Values window run the case again – now you have JetEnergy as additional output.

Next let us have a look at the Enthalpy-Entropy diagram of the cycle

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Enthalpy-Entropy Diagram

Click here to open the slider definition window.

We now freeze this diagram for making comparisons with another

cycle.

The diagram shows real numbers. See how it

changes with compressor pressure ratio

Click to reduce to one

slider only

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Using the Slider…

Move the Slider to the right – this increases

Pressure Ratio.

Now you see how the pressure ratio of the compressor affects the hot section

part of the cycle

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Single Cycle Output

This is again the original cycle. The turbine pressure ratio of 3.178 is easily achievable with a single

stage turbine. In fact, a single stage turbine can work up to a pressure ratio of 4 with an acceptable efficiency.

Let us search for the compressor pressure ratio which yields exactly the turbine pressure ratio of 4. Close this window to proceed.

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Single Cycle Input Data Page

We will vary (iterate) compressor Pressure Ratio in such a way that

Turbine Pressure Ratio is equal to 4.

We open now the Iterations input window.

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Iteration Variable Input

Min and max boundaries for the variable are required for numerical

reasons. The min and max values need not to be accurate, they are for excluding physical meaningless numbers (like very low pressure ratios) from the

calculations.

From all the input Variables we choose Pressure Ratio and drag it from the selection tree to the table.

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Iteration Target Input

From all the output quantities we choose Turbine Pressure Ratio as

Target and drag it from the selection tree to the table.

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Iteration Target Value Input

Enter the target value here…

…and activate the iteration.

Then close the window.

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Single Cycle Input Data Page

Now we are ready to run the case

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The Cycle with Turbine Pressure Ratio = 4

This slide ends the Single Cycle Tutorial