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OPTIMIZING A CYCLE

GasTurb 12 – Tutorial 4

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GasTurb 12 Main Window

For this tutorial we will use a Turbojet.

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We Need Some Data

Select the engine model

Open the engine model

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Input Data Page

First we run a single cycle

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Starting Point of the Optimization

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Optimization Task:Find the Compressor Pressure Ratio for Minimum SFC

The SFC minimum is at pressure ratio 65

The optimization feature allows finding

the SFC minimum without doing a

parametric study.

A parametric study with Pressure Ratio as

the only parameter yields…

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Selecting Optimization

Now we go for Optimize.

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Optimization Input Window

The Min Value must be lower than the Start Value

The Max Value must be higher than the Start Value

First drag the Optimization Variable to the input grid.

Next enter boundaries for the variables.

Finally define the Figure of Merit

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Optimization Input WindowThe Figure of Merit can be

maximized or minimized. Of course SFC shall be minimized

Drag your Figure of Merit to the box.

Now run the optimization

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The Optimization Window

The upper boundary(Max Value)

for the variable

The lower boundary(Min Value)

for the variable

Click to run the optimization

Let us have a look at the result.

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SFC Optimum

This result is somewhat unrealistic for a turbojet - among other reasons because the turbine pressure ratio is

almost 24.

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Repeating the Optimization

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Repeating the Optimization

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Introducing Constraints

The Min Value must be lower than the Start Value The Max Value must be

higher than the Start Value

We introduce as Constraint the Turbine Pressure Ratio.

We enter for the upper boundary (Max Value) 4. This is a reasonable

limit for a single stage turbine. The Min Value is of no relevance for this

optimization problem.

Then we re-run the optimization.

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End of the Constrained Optimization

The value of the optimization variable is within the Min and

Max Values

The value of the optimization constraint is equal to the Max

Value

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Result of the Constrained Optimization

Turbine Pressure Ratio is 4

This introduction to optimization was very simple. The problem

could have been solved also with a simple parametric study.

Next we go for a more complex task which would require many

parametric studies for finding the optimal solution.

Applying numerical optimization leads quickly to the result.

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GasTurb 12 Main Window

The file opening menu will appear automatically, read the file

Demo_gtf.CYG

After reading the data, the design input window opens.

We will consider a Geared Unmixed Flow Turbofan.

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Input Data Page

First we run a single cycle

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Starting Point of the Optimization

After closing this window click Optimization.

Then, hit the Optimize button.

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Optimization Input

There are five optimization variables…

… and three Constraints.

The Figure of Merit is again SFC

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Optimization Status

Let us have a look at the optimum

Status at the begin of the optimization

Status at the end of the optimization

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Result of the Optimization

LPT Pressure Ratio <=12

T45 <=1300K

Net Thrust >= 31 kN

The solution fulfills the Constraints

The SFC was previously 16,60, Optimization has reduced it by 4.6%.

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Optimization Input

Do all of these constraints really apply to Cruise

conditions?

We have optimized the cycle for minimum SFC

at cruise conditions. However, …

No ! the LPT Inlet Temperature T45 Limit must not be

exceeded during a hot day Take-Off.

Next we will show how this can be taken into account.

Go back to the GasTurb Main Window. When asked to restore the old data, chose

“Yes”.

GasTurb 12 Main Window

Select Off Design…

…and Standard Maps

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Select the Mission Option

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Mission Input

Choose a Single Point Mission and enter the Take-Off operating conditions as well as the required

thrust of 145kN

Run the Single Point Mission and check if the off-design

iteration converges.

Close the Mission Windows and go back to the GasTurb12 Main

Window. Switch back to the Calculation Mode Design and

select Performance.

In the Design Input Window click Optimization and Run.

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Design and Off-Design Constraints

These dropdown lists are visible only if a mission is

defined.

Select “Case 1” to apply the T45 constraint to the

off-design condition.

Click Constraints

After the Optimization RunC

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The Cycle Design Point

LPT Pressure Ratio <=12

T45 is not constrained at

the cycle design point

Net Thrust >= 31 kN

The SFC was previously 16,60.Single Point Optimization yielded 15,83. but T45 at Hot Day Take-Off was 1324K.

With additional constraint for Off Design (T45 <= 1300K), SFC is reduced by 3.9%.

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Hot Day Sea Level Take-Off

T45 <=1300K

This slide ends the Control System

Optimization Tutorial