Transcript GasTurb 12: How to Calculate a Single Cycle

GasTurb 12 – Tutorial 1
Copyright © GasTurb GmbH
HOW TO CALCULATE A
SINGLE CYCLE
A Jet Engine Example
The Program offers
three
Scopes
that differ
For
professional
in
the
amount
of detail
performance work
use the
being
simulated.
The
Engine Design option.
Choose Basic
Performance
Thermodynamics
or…
scope is least
demanding for the user.
More…
if youtextbook
want to
Only simple
determine
the
engine
wisdom is considered.
geometry.
Copyright © GasTurb GmbH
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
Copyright © GasTurb GmbH
We Need Some Data…
Cycle Design Input Data Window
Copyright © GasTurb GmbH
All input is in clear nomenclature
- no cryptic abbreviations are
used.
Switching to Imperial Units is
easy
Let’s go back to SI Units
Thermodynamic Station Input
Copyright © GasTurb GmbH
Click here to start
the calculation
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.
Copyright © GasTurb GmbH
Single Cycle Output
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reminds of the outdated
designation
weight flow.
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 and
W is employed for mass flow.
Explanations are at your fingertip: Click a symbol –
for example TSFC - and you get a detailed
explanation.
Thermodynamic Station Output
Copyright © GasTurb GmbH
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.
Getting Additional Output
I need to know a
cycle property
which is not listed
on the output page.
Copyright © GasTurb GmbH
Open the Composed Values
window – a powerful formula
editor.
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
Copyright © GasTurb GmbH
Example: Calculate the kinetic energy of the nozzle exhaust
JetEnergy=W8*V8^2/2
Dividing by 1000 yields the Jet Energy in kW
Copyright © GasTurb GmbH
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 EnthalpyEntropy diagram of the cycle
Enthalpy-Entropy Diagram
The diagram shows real
numbers. See how it
changes with compressor
pressure ratio
Copyright © GasTurb GmbH
Click here to open the
slider definition window.
We now freeze this diagram for
making comparisons with another
cycle.
Click to
reduce to one
slider only
Using the Slider…
Copyright © GasTurb GmbH
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
Copyright © GasTurb GmbH
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.
Copyright © GasTurb GmbH
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.
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.
Copyright © GasTurb GmbH
From all the input Variables we
choose Pressure Ratio and drag it
from the selection tree to the table.
Iteration Target Input
Copyright © GasTurb GmbH
From all the output quantities we
choose Turbine Pressure Ratio as
Target and drag it from the selection
tree to the table.
Iteration Target Value Input
Enter the target
value here…
Copyright © GasTurb GmbH
…and activate
the iteration.
Then close the
window.
Single Cycle Input Data Page
Copyright © GasTurb GmbH
Now we are ready to run the case
Copyright © GasTurb GmbH
The Cycle with
Turbine Pressure Ratio = 4
This slide ends the
Single Cycle Tutorial