integrated modeling for aerospace powerplant system...

Integrated modeling for Aerospace Powerplant system assessments

Presented by Borja DÍAZ SOTO Airbus Military Work Package Leader of Powerplant Simulation Heat management system focal point – Oil & Fuel assessments.

Aug 2011

© AIRBUS Military. All rights reserved. Confidential and proprietary document.

General Background

• Airbus Military Powerplant Department is in charge of integrating all the systems related

to the powerplant within the complete aircraft.

• In particular, the integration of a turbopropeller represents a complex multidisciplinar

problem, which embeds several subsystems (not always related to pure engine

systems).

• Support on very different topics is needed in consequence. For instance:

• Nacelle integration & Ventilation

• Oil system integration

• Fuel system integration

• Electrical supply and integration i.e. electrical generators coupled with the oil

system

• Electronic control of the engine.

• All the equipments and fluid circuits are required to fulfill the applicable regulation

issued by the corresponding authorities.

Aug 2011

Interaction with heat exchangers (i.e. ACOC)


General Background

• The previous regulation requires demonstration of all subsystems temperatures to be

within limits This demonstration is accepted to be covered by different means: flight

test, specific assessments…etc.

• For those activities that cannot be performed by flight test (i.e. due to safety

constraints, time schedule) the development of a dedicated model is completely

needed.

• The following slides are intended to provide an overall view of the importance of

coupling both CFD, flight test analyses, pipes modelling for 2 particular assessments:

1. Oil system integration into the complete aircraft ACOC heat exchanger,

interaction between air and oil.

2. Analysis of an air duct rupture embedded into the nacelle and its potential

consequences in terms of pressure.

Aug 2011


1.- Oil system model integration

Objective: to ensure compliance of the maximum temperature limits of the oil circuit.

Scope: Heat rejection coming from the different turbomachinery, propeller gearboxes etc

is leading to very high oil temperatures, which have to be fixed by means of a dedicated

heat exchanger.

Integration problem: In particular, an ACOC (Air cooled Oil Cooler) heat exchanger is

considered, with the interaction between the air passing through a predesigned duct,

and the oil circulating through the circuit.

Analysis: The simulation for the following conditions:

• Each power condition.

• Each aircraft altitude.

• Each aircraft velocity.

• Each ambient temperature.

• Each exit area (it is variable).

has to be ensured Thus, the simple application of a CFD analysis is not appropriate

due to schedule constraints.

Aug 2011



Methodology: limits of the oil circuit have to be checked at different points, and

temperatures are all interdependent It is needed to integrate a model of the oil

behaviour with the model of the heat exchanger.

A/. Development of the oil components behaviour with a 1-dim / 0-dim tool (i.e.

Simulink, EcoSimPro, Flowmaster…).

1. Based on manufacturer characteristics:

Aug 2011

Characteristics, flows,

heat rejections

implemented into the

model



2. Based on test results:

3. Based on simple models/subanalysis (i.e. ESDU papers, technical documentation)

Aug 2011

Correlations

and further

implemented

into the model

Epsilon – NTU method

for the effectiveness

of the heat exchange



The final model assembly is performed in a 0-D or 1-D suite (i.e. Simulink):

Aug 2011

The ACOC part

needs the airflow

to calculate heat

exchange



B/. Coupling the airflow problem Architecture:

• One inlet duct in the bottom part of the nacelle

• Heat exchanger

• Outlet duct with a variable exit area (flap device)

Aug 2011

Characteristics, flows,

heat rejections

implemented into the

model

Nacelle

The variable exit area makes the airflow change,

thus regulating the total amount of heat exchange

between air and oil



1. To use a CFD tool to compute each case NOT FEASIBLE solution, never-ending assessment.

2. To use a “simple” model, based on existing documentation (ESDUs etc) and

the already available sensors within the duct.

• After coupling this model with the oil part, the prediction is very poor

(30degC of error in temperature prediction).

• It is needed to elaborate a new strategy, based on the use of CFD

modeling plus the installation of some new instrumentation.

Aug 2011



3. To use a CFD tool to develop an airflow model, then couple the two models. Two

different approaches:

• To use the duct geometry to run a set of representative cases (CFD). Then use

• To use the CFD tool to identify the best place for installing instrumentation.

Then use test data to obtain correlations:

Aug 2011

Due to pressure gradients, it is

needed to install several probes

even in the same section, to

characterise the airflow. CFD

allows to know the correct

positions.

After the heat exchanger matrix,

the total temperature is not

uniform, and some extra probes

were needed to capture this effect.



• Where the different parameters of the equations were obtained from the

instrumentation previously defined relying on the CFD.

• After validating the airflow model versus the sensed values, the expected accuracy is

+/- 5% of relative error, so thanking to the CFD model the prediction error can be

decreased as much as possible.

Aug 2011



The obtained accuracy of the complete model (air+oil) is +5degC for the oil temperatures

Aug 2011



4. For the computation of specific conditions (not nominal conditions), to run the CFD

model directly. In particular:

• Aircraft in reverse condition reverse flow through the duct.

• Low power condition on ground where low amounts of airflow are in place

(low momentum).

Aug 2011

For reverse case, the CFD

computation provides the

best understanding on the

airflow behaviour.

(Model predictions are

not valid for this case).

In particular

Figures 1 and 2 represents

static temperature isolines

for the total exit area,

and a partial exit area

Respectively.

Figure 1

Figure 2


1.- Oil system model integration.

CONCLUSION

In order to cope with the needed assessments, several cases had to be evaluated:

- 500 tests to be performed for validation

- Improvements of the nacelle integration usually drive to trade-offs of several values, or

implementation of solutions which need multiple simulations varying different

parameters.

- The use of an isolated CFD for each case is not feasible in terms of schedule, and the

best way to proceed is to integrate CFD models / results with parallel 0-D and 1-

Dimensional models.

- By developing a joint model, the timeframe is reduced in a extreme critical way, and

CFD tools (i.e. CD-adapco ones) provide the relevant results required by Airbus

Military as aeroespace powerplant integrators.

Aug 2011


2.- Duct rupture model integration

Objective: to ensure compliance of non-structural damage in the nacelle (due to high

pressure loads and high temperatures in the cowlings).

Scope: when a bleed duct passing through the nacelle is suddenly broken, there is a great

amount of airflow being discharge inside. This potentially leads to very high structural

loads (unsafety condition) and high temperatures not supported by the carbon fibre

components.

Integration problem: General arrangement of the components inside the nacelle is not

uniform nor symmetric. Thus, the airflow is not distributed uniformly and the pressure

losses are not easily simulated.

Analysis: Once the critical situation of the discharge (high bleed pressure and high bleed

temperatures) are identified, the simulation of the case leads to a CFD computation.

• In case of not fulfilling requirements, it is needed to study an alleviation of the

problem, which leads to a trade-off consisting of several simulations (varying

some parameters) In particular, installation of a blow-out panel in the

cowlings, designed to be opened in case of a rupture, therefore decreasing the

internal pressure.

Aug 2011



• Structural arrangement of the nacelle does not allow the installation of the

panels anywhere, and a trade-off of total area / location has to be performed in

consequence.

• Thus, several simulations have to be performed for each area condition and

again, the use of an isolated CFD tool is not feasible in terms of schedule.

• It is needed to develop a 1D model (this time using other commercial tool) to

assess the cases but based on the characteristics of the nacelle.

• No test is available for this condition (rupture, unsafe) CFD computations are

the intended tool to provide the basis of the 1D model that will extrapolate each condition.

• Way forward: to use a CFD model to obtain the pressure loss characteristics of the air along the nacelle, and incorporate them into the 1D model.

Aug 2011



Aug 2011

• Problem solving: nacelle is divided in the different stations (sections of the

engine), and differential pressure is obtained at each of these stations for different conditions.

• For instance, for outlets, a discharge pressure correlation is obtained from CFD:



Aug 2011

• The following plot illustrates a typical equivalent are dependency with the

airflow (used to characterise the inlets):

Which is at the same time dependent on the aircraft angle of attack in this

case.



Aug 2011

• To obtain the previous curves, the aerothermal CFD model of the complete

nacelle is needed, since the presence of every component is affecting the

differential pressures. This model is owned by the Aerodynamics department in

Airbus Military.



Aug 2011

• So by incorporating all the pressure characteristics in a one-dimensional

model, as simple relationships with typical aerospace inputs:

The area of

the panel

becomes

an input



Aug 2011

• Once the model is ready, a simulation of the nominal case is performed.

• This represent the case of Area=0 Now a trade trade-off is performed by

increasing the area, obtaining the optimum so that the total pressure does not

exceed the limits:



Aug 2011

CONCLUSION

• After the simulation of the different areas, other devices can be added in

consequence to the model in order to seek for alternative solution.

• The simulation of all these cases (blow out panel inclusion, trade-off of

different pressures, other devices, etc) were not feasible by simply using a

CFD model for each case.

• The use of the 1D model coupled with simulations results provided by CFD

tools (like CD-adapco ones) can save plenty of time and money to the

nacelle integrators.


Aug 2011

© 2011 AIRBUS. All rights reserved. Confidential and proprietary document. This document and all information contai ned herein is the sole property of AIRBUS. No i ntellec tual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or discl osed to a third party without the express written consent of AIRBUS. This document and its content shall not be used for any

purpose other than that for which it is supplied. The statements made herei n do not constitute an offer. They ar e based on the menti oned assumptions and ar e expressed in good faith. Where the supporting grounds for

these statements are not shown, AIRBUS will be pleased to explain the basis thereof. AIRBUS and AIRBUS MILITARY them logo, A300, A310, A318, A319, A320, A321, A330, A340, A350, A380, A400M, A330MRTT,C212,C295,CN235 are registered trademarks

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