Automotive transient thermal modeling seminar draft 5

Sudhi Uppuluri, CSEG LLC

Andrew Hintz, Mentor Graphics

Automotive Transient Thermal Modeling Seminar

www.mentor.com© 2012 Mentor Graphics Corp. Company Confidential2

Why do we care?

Many Technologies being explored/implemented to meet CAFÉ standards. And they don’t always work well together!

Automotive Transient Thermal Modeling Seminar, 2013, 09, 12


Integrated System Simulation is the only way!

Many Supplier offering fuel economy technologies!— Some may not work as well for your system

OEM’s have the responsibility as system integrators to evaluate and cherry pick the technologies based on benefit/price ratio!


www.mentor.com© 2012 Mentor Graphics Corp. Company Confidential

Why is Engine Thermal Management important?

Cold Engine = Bad Fuel Economy

— Incomplete combustion

— Increased thermal losses through the combustion chamber walls

— Increased friction losses with the increase of the lubricant oil viscosity.

Frictional losses reduce as engine warms up

Reference: 2000-01-0299

4 Automotive Transient Thermal Modeling Seminar, 2013, 09, 12


Why Engine Thermal Management Modeling is hard!

Why Engine

Thermal Manageme

nt Modeling is hard!

Responsibility fragmented across the organization

Model is data

hungry

Data not readily

available

Majority of data

is steady-state

Experimental procedures

are for validating

designs, not models

Requires expertise

across multiple subjects



Modeling Considerations

Drive Cycles



Flow of Today’s Talk

Overall Engine Thermal Model— Engine Structure sub-system— Cooling System sub-system— Front-end cooling pack sub-system— Cabin Model— Engine Oil Sub-system— Trans Oil sub-system

Modeling and evaluating FE improvement technologies— BSG (Start-Stop Scenario)— Dual Use heater core technology

Integrating with Control System/Vehicle Models Simplifying models into a response

surface/equation



Introductions

CSEG Premier Consulting

Company on System Simulation

Mentor Graphics Consulting partner for advanced system modeling

> 25 yrs combined experience modeling automotive systems

Wide variety of tools including Flowmaster, Matlab/Simulink, GT Power, FloEFD, and custom application development in .NET

Mentor Graphics Application Engineer 5 years experience in

variety of industries and applications

Primary automotive engineer for Mechanical Analysis Division, including vehicle thermal management, hybrid/electric, exhaust, airside, cabin comfort, and lubrication modeling.



Flowmaster V7 is a System Level CFD Simulation Software Program, enabling analysts and engineers to perform System Simulation to the design, validate, optimise and maintain complex fluid systems

— Pressure, temperature, and flow predictions— Liquid, gas, steam/water systems— Steady state & transient— Heat transfer— Design of experiments & parametric studies— Component sizing & flow balancing— Simulation Data Management— Built-in Empirical Data

System Modeling Platform



What is Flowmaster?

Project View Schematic View Network View



Sub-systems: Engine

Component – Engine: Basic— Pressure loss

– Fixed Loss Coefficient– Pressure loss vs. velocity– Pressure loss vs. volumetric flow rate– Pressure loss vs. volumetric flow rate

and temperature– Loss Coefficient vs. Reynolds

number*— Thermal inertia

– Solid type & mass– Initial temperature



Sub-systems: Engine

Component – Engine: Basic— Heat Generation

– Heat Flow Rate– Fixed value– Heat flow rate vs. time– Signal input

• Customizable heat flow rate dependency

— Heat Transfer Coefficient– Dittus Boelter coefficients– Fixed value– Heat transfer coefficient vs.

Reynolds number– Signal input– Nusselts number vs. Reynolds and

Prandtl #s



Modeling Engine Structure

◦ Capturing every heat transfer path (more components = more data required)

Reference: SAE paper 910302, Kaplan and Heywood.



◦ Capturing every heat transfer path (more components = more data required)

Reference: SAE paper 960073, Bohac, Baker and Assanis.





Capturing minimum number of masses to predict warm-up



Get Heat additions/removal correct

+Qcomb

+QFric

Heat Loss to the ambient (Conduction + Natural convection + Forced convection)

Heat Loss to the Coolant

Heat Loss to the Oil

Heat absorbed by the mass



FMEP – Through analytical methods

Your Initials, Presentation Title, Month Year


Sub-systems: Cooling System

Component – Pump: Water Pump— Suter Head Curve*

– Pressure rise vs. rotational speed and fluid flow rate

— Suter Torque Curve*– Power consumption vs. rotational

speed and fluid flow rate— Rated data

– Flow– Head– Speed– Power or Efficiency



*Suter Curves

Normalized curves (with respect to pump’s rated condition) describing variation in head or torque over full range of operating conditions— Utilizes Homologous Pump Laws

Suter curve conversion tool available in Flowmaster




Component – Pump: Test Data Supplier data can be directly

input into the model




Component – Thermostat— Control amount of fluid routed to

Radiator– Lift vs. temperature

– Defines valve’s position as function of fluid’s temperature

– One for heating, one for cooling– Alternatively, define Hysteresis offset

and one Lift vs. temperature curve— Bypass opening vs. opening

– Defines opening to bypass as function of opening to Radiator

— Simplified pressure loss– Loss Coefficient vs. opening

— Time Constant– Transport delay between coolant and

wax



Transient Considerations on TSTAT

Time Constant is the time it takes TSTAT to open to 63% opening on a step change of temperature




Component – Reservoir: Expansion Tank— Tank dimensions

– Height of top above base– Height of each inlet/outlet with

respect to base– Height of base above “sea level”– Volume

– Constant horizontal cross-sectional area

– Cross-sectional area vs. height– Volume vs. height

— Initial pressure, temperature, liquid level

— Pressure loss at each arm for inflow & outflow scenarios

— Hard pressure constraints– Mimic functionality of pressure relief

or vacuum relief valveAutomotive Transient Thermal Modeling Seminar, 2013, 09, 12



Component – Reservoir: Expansion Tank— Thermal capacity of tank

– Tank material– Mass of empty tank

— Heat transfer between tank and environment

– Heat transfer coefficient– External surface area– Environment temperature

— Tank expansion– Reference pressure and temperature,

and Poisson’s Ratio– Surface of volume change vs.

pressure change and temperature change




Component – Heat-Exchanger: Radiator— Independent pressure loss data for

hot side and cold side– Fixed Loss Coefficient– Pressure loss vs. flow rate– Pressure loss vs. velocity– Loss Coefficient vs. Reynolds

numbers




Component – Heat-Exchanger: Radiator— Thermal interaction between fluids

– Fixed thermal duty– Fixed hot or cold side temperature

change– Fixed thermal effectiveness– Effectiveness vs. hot side flow and

cold side flow– Heat transfer coefficient (q/ITD*area)

vs. hot side mass flow rate and cold side mass flux (mass flow/area)

– Fixed overall heat transfer coefficient + effectiveness vs. number of transfer units and specific heat ratio

– Nusselt number vs. hot side and cold side Reynolds numbers*



Transient Modeling Considerations

Loss Coeff vs Re curve accounts for changes pressure drop changes at different temperatures.

This is critical when running at different drive cycles.



Transient Modeling Considerations

Preferred Approach as NU extrapolates well

Effectiveness is held constant outside the test data. And we are always operating outside the test data.



*Loss Coefficient vs. Reynolds number

Pressure loss vs. fluid flow valid for specific fluid property

As fluid properties change, pressure loss changes

Loss Coefficient vs. Reynolds number— Reynolds number is ratio of inertial forces to viscous

forces– “Flow condition” based on fluid’s properties and fluid flow

— “K” value in first equation now varies with fluid properties and flow rate

— Higher accuracy in pressure loss calculations



*Loss Coefficient vs. Reynolds number

“Loss Curve” conversion tool available in Flowmaster— Convert pressure loss vs. flow curve to Loss Coefficient

vs. Reynolds number



*Nu vs. Rehot & Recold

Flowmaster conversion tool for Nusselt surface more “free-form”— Define hot and cold flow

– Volumetric or mass flow– Mass flux

— Thermal performance – Heat duty– Effectiveness– q/ITD*area– Exit hot side temperature– Exit cold side temperature

— Additional data– Hot and cold fluid types– Inlet hot and cold temperatures and pressures



Sub-systems: Front End Air Cooling

Freest

ream

Freest

ream

Un

derb

od

y/U

nd

erh

ood

Fan

Rad

iato

r

Con

den

ser/

EO

C

Ch

arg

e A

ir C

oole

r



Non-uniformity of flow

Reference: A Systems Engineering Approach to Engine Cooling Design, Kanefsky, Nelson and Ranger, SAE Lecture, SP-1541

There is non-uniformity in airflow and temperature in the cooling pack.

Segmentation is one way to capture the non-uniformity accurately (Need to collaborate with CFD to determine non-uniformity at different driving conditions)

Nusselts number is the recommended way when modeling segmented heat exchangers.




Airside Visualizer and Segmenter (AVS)— Model a cooling pack where airflow through each

component is not equal– Doesn’t easily lend itself to 1D modeling

— Segments model in such a way to align common flow paths

Fig 60 image Reference: A Systems Engineering Approach to Engine Cooling Design, Kanefsky, Nelson and Ranger, SAE Lecture, SP-1541




Arrange components in 1-D manner— Add visualizer and

segmenter data for components in airside path

– Defines spatial arrangement of components

— Profile parameter options– Non-uniform parameters

— Running visualizer provides 3-D representation




Component – Radiator Shutter— Dimensions

– Height and width— Shutter opening

– Fixed value– Signal input

— Visualizer and Segmenter data— Pressure loss

– D.S. Miller data




Segmenter divides cooling pack into 1-D segments— Define split planes

– Number of splits– Spacing of splits– Manually define split plane

— Overlay split planes




Segmented results



Front-end Cooling Pack Calibration

Accurate CFD under hood airflow information



Sub-systems: Charge Air

Component – Turbo Charger— Compressor performance data

– Pressure ratio vs. corrected mass flow and corrected rotational speed

– Efficiency vs. corrected mass flow and pressure ratio

— Turbine performance data– Corrected mass flow vs. pressure

ratio– Efficiency vs. corrected mass flow

and pressure ratio



Transient Conditions – Determination of ACT

Inputs are Charge Air Mass flow rate and temperatures

Air Charge Temperature (ACT) determined for the engine drive cycle Co-simulated with the combustion program



Sub-systems: Engine Oil

Component – Closed System Sump— Two-arm reservoir— Sump is within the system— Initial liquid level, pressure, and

temperature specifier— Define volume— Thermal capacity of tank

Component – Open System Sump— One-arm reservoir

– Open-system offers a bit more stability

— Sump modeled as boundary condition

— Liquid level, pressure, and temperature specifier




Component – Oil Pump Strainer— Based off Orifice: Square

component— Full flow area and orifice flow area— Loss coefficient vs. area ratio

– Default D.S. Miller data




Component – Pump: Oil Pump— Positive displacement pump— Rotational speed

– Fixed value– Signal controlled

— Volumetric displacement– Fixed value– Surface map

– Flow and power vs. pressure rise and rotational speed

– Requires reference viscosity– Signal controlled

– Total displacement– Displacement ratio

— Pump coefficients– Leakage, Coulomb friction, Viscous

friction




Component – Pressure Regulator— Three-arm component

– Through branch– Relief branch

— Sets pressure limit as function of flow rate

— When limit is reached, relief valve opens




Component – Oil Filter— Pressure loss component

– Specify fixed loss coefficient– Pressure loss vs. flow or velocity– Loss coefficient vs. Reynolds number




Component – Journal Bearings— Geometry of bearing

– Groove, bore, pocket— Rotational speed

– Fixed value– Vs. time– Signal controlled

— Rotating or rocking— Average clearance bearing to

journal– Fixed value– Signal controlled

— Bearing force– DIN (cycle averaged)

– Fixed value– Vs. time– Signal controlled

– Booker-Martin (discrete cycle angles)




Component – Passage: Rotating— Pipe component that accounts for

pressure fluctuations due to centrifugal forces

– Define position of end points in relation to shaft

– Define motion– Circular– Piston/Slider– Cam Follower

Component – Loss: Bearing Entrance— Using in conjunction with Passage:

Rotating– Models oil flow from groove, bore, or

pocket of bearing to rotating hole in journal



Sub-systems: Cabin Comfort

Component – Cabin— Solar radiation definition

– Direct and diffuse radiation– Fixed value– Vs. time

– Ground reflectivity– Azimuth and altitude angle

– Fixed value– Vs. time



Component – Cabin— Key results

– Mean cabin temperature– Temperatures of different locations

– Roof, screen, instrument panel, etc– Cabin comfort

– Predicted percentage dissatisfied– Predicted mean vote




Modeling multi-zone passenger cabin



Integrating Sub-systems



Technology Evaluation – Belt Starter Generator

Enables turning off engine when idling

Efficient and high power generation

Transient Considerations – — BSG head load and thermal

inertia— Effect to engine thermal

performance— Temperature of BSG (safe

operating temperatures)




Thermal Load of BSG

Zero Flow Heat Transfer

in engine block




Warm-up is affected as engine turns off during engine idle



What is Zero Flow Heat Transfer (ZFHT)?– ZFHT allows heat transfer analysis

where flow conditions are below Flowmaster’s minimum flow threshold

Background— Modern automotive cooling

strategies use ‘low’ or ‘zero’ coolant flow to achieve rapid engine warm-up for

– Reduced emissions– Increased fuel economy




Suitable for any single phase network that is…— Wholly, or partially, subject to

‘zero flow’ at some point in its operating cycle

— and intended for Incompressible HT analysis

A standard feature of the ‘Heat Transfer’ Option

Currently focused on cooling system analysis but can be used for any liquid application where the user needs to predict— HT in one or more static circuit— Resulting temperature values

Key user defined BCs include convective HTCs which are typically from:• 3D CFD component/sub-assy

models• Experimental results (i.e.

thermal survey of engine cooling system)

• Experience of a similar system

Zero Flow HTSystem simulation• HT Steady State• HT Transient

Predicted results for system• Heat transfer

distribution• Temperature profile

Zero Flow HT is…




Technology Evaluation – Dual use Heater Core

Dual Use Heater Core – Heater Core is used to provide supplemental engine cooling, without affecting cabin comfort.




The effect on AGS closure rate, and required fan size can be performed with supplemental Engine Cooling model

AGS open control

Fan Size

Heater core airflow




AGS CLOSE

D

AGS OPEN

AGS Closed for significant portion of the time




Stable control of engine oil temperature



Technology Evaluation – Dual use Heater Cooler

X CFM through Heater Core leads to

1.5X CFM reduction in Front end airflow (when AC is OFF)

1.2X CFM reduction in Front end airflow (when AC in ON)



FLOWMASTER FOR SIMULINK

68


Flowmaster for Simulink

A Flowmaster library providing an interface between Simulink & Flowmaster comprising allowing co-simulation between Flowmaster & Simulink.

The link comprises — A graphical user interface to configure the link— A Simulink S-Function to interface between Flowmaster &

Simulink



Simulink Library Browser


Analysis Process




The Flowmaster for Simulink interface in Simulink




Interface to more than one Flowmaster network during a Simulink simulation




Configuring a Flowmaster Network— Data is passed into and out of Flowmaster using COM

Controller & Gauge Components– Data in via COM Controller– Data out via COM Gauge

COM GaugeCOM Controller




Configuring Flowmaster Controllers & Gauges— Each Controller and Gauge being used to in the link must

have a unique ‘Title’ set on the component data form




Configuring Simulink— Data is passed into the Flowmaster block using a “goto”

block– “goto” block tag visibility must be set to Global

— Data is passed from Flowmaster block using a “from” block



RESPONSE SURFACE MODELING

76


Experiments: Response Surfaces & Meta-Models

Features— A Meta-model contains

simulation results sets, all defined input parameters, a selected output parameter and a radial function

— A Response Surface is a 3D plot of two selected input and one output parameter with an applied radial function

What it does— Provides a visual

representation of a Flowmaster system Meta-model

— Provides a means of evaluating the Meta-model prior to export as C code or an S-Function

Deviation tools to assess quality of the meta model

Response Surface generated in V7.9.1



FM Application v Response Surface Model

Inputs Outputs

Inputs Outputs

• Design and model• Infinitely variable• No guarantee of convergence• Not real time simulation

• Pre-defined system• Bounded simulation• Guarantee of convergence• Real time simulation

Flowmaster V7 Application

Response Surface Model



Simple Cooling Circuit example

Heat Load

Radiator

Front-end airflow

Bypass valve position

Target TempPump Speed

m_bypass

m_total

m_rad



Response Surface Generation



Creating an Response Surface in Flowmaster

A Response Surface is created in the following steps

Select a Radial

Function

Select Results set

Select Input

Parameters

Select Output

Parameter

Click Display



Creating a Response Surface

A radial function is selected

The radial functions available are— Gaussian— Duchon’s— Hardys— Inverse MultiQuadrics



Radial Functions

The following radial basis functions (RBF) were selected from common usage— Gaussian

— Duchon’s

— Hardy’s

— Inverse MultiQuadric

*where Φ(r) is the radial function and r0 is a scale factor and r is the radial distance between points



Creating a Response Surface

Two input parameters are selected for the plot and one output parameter Clicking ‘Display’ shows the 3D and two 2D plots



Evaluating a Response Surface

The effective fit of the applied radial function can be evaluated from the available deviation plots

Percentage deviation is calculated as the percentage difference between a results point and an interpolated point derived from the fitted curve

The Response Surface can be refined by selecting an alternative radial function, or if available alternative results sets e.g. with more or fewer levels




Deviation details (2D scatter chart)

Surface plot points

Deviation mean line

Plotted deviation points(lower is better)




3D Deviation plot

Input parameters

Deviation points as surface plot



Export Code Examples

C code or an S-Function can be exported from a saved Meta-model by clicking the export button

C code S-Function code



Today’s Talk

Overall Engine Thermal Model— Engine Structure sub-system— Cooling System sub-system— Front-end cooling pack sub-system— Cabin Model— Engine Oil Sub-system— Trans Oil sub-system

Modeling and evaluating FE improvement technologies— BSG (Start-Stop Scenario)— Dual Use heater core technology

Integrating with Control System/Vehicle Models Simplifying models into a response

surface/equation


Automotive transient thermal modeling seminar draft 5

Automotive

Transcript of Automotive transient thermal modeling seminar draft 5