brake analysis-temperature approach

5/27/2018 Brake Analysis-Temperature Approach

1/19

Thermal Analysis of a Vehicle DiscBrake in a Multi-Stop Scenario

Josh Pryor | [email protected]


2/19

2

Introduction

Disc brake simulations can becomplex to mesh and setup

Previous UGM talks havediscussed: Meshing techniques (shell vs. solid)

Heat application techniques CFD convection

This effort starts from a solid-meshed vented disc brake

Main question: how to effectivelyuse CFD for a multi-stopscenario?

2


3/19

3

Convection options

RadTherm convection (automatic library or assigned HTC) Fast and easy to setup

Difficult to capture effects of vent designs or upstream flow effects

(vents, shields, etc.) Typical transient CFD coupling

(local fluid temperature-based HTC): Run multiple steady-state cases corresponding to different points in

time of a RadTherm transient model

Different CFD case is needed anytime flow conditions or surfacetemperatures change significantly Depending on the stop profile, this most likely requires 6-20 CFD cases

per stop (60-500 total cases!)

One-way CFD coupling(reference fluid temperature-based HTC): Assume that convection effects are primarily based on flow conditions

(which are cyclical) and not on local surface temperatures

Run enough CFD cases to cover velocity profile of one stop (6-20total cases)


4/19

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Thermal model

Brake geometry only Rotor, pads, caliper

Heat applied to pad surface

Pads linked to rotor with generic thermal

link (intermediate node approach) 276,000 total elements

Rotor & pads primarily hexa & prismelements

Caliper uses tet elements


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CFD model

Front quarter-car model Includes heat

exchangers, grille, frontfascia, basic underhood,

wheels/tires,suspension, brake parts

5.7 million volumeelements (polyhedral)


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CFD selected cases

6 points were used tocharacterize the velocityprofile for each stop

6 cases are set up andrun for eachcorresponding velocity Surface temperatures

estimated from middle stopof standalone thermal model

Reference temperatureapproach: Convection from these 6

cases are importedrepeatedly to capture fullprofile


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Selecting the convection coefficient

reference temperature Most straightforward approach is to use the ambient

temperature as the reference This will result in valid convection coefficients if all surface elements

in question are experiencing local cooling

This works well for hotter parts (rotor/pads), but breaks down forcooler parts (caliper)

In this model, the caliper was experiencing local heating

Reference temperature therefore needs to be hotter than the typicalcaliper temperature and cooler than typical rotor temperature

57o C was used

This temperature is consistent with typical fluid temperatures near the

brake (due to heating from the brake and underhood) and results inrealistic convection coefficients


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Importing CFD Results

After 6 neutral files arederived from CFD cases

with convection data, eachmust be imported 20 times Once during speed-up and

slow-down of each stop

Batch script is used toautomate this process radtherm importCFD

settings.txt save model.tdf Before each import, the time

value in settings.txt isreplaced with the next value


9/19

9

CFD Flow Results (50 kph)

Wheel-well vent has

little impact on brake Most incoming

flow from

under wheel-

well

Some from

underhood


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CFD Convection Results

96 kph 67 kph 50 kph 38 kph 19 kph 4 kph


11/19

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Thermal Results

Part average temperatures

0

50

100

150

200

250

300

350

75 175 275 375 475 575 675 775 875 975

Time (s)

Temperature(degC)

Rotor contact face (inboard) Rotor contact face (inboard) (standalone)

Rotor Rotor (standalone)

Pads Pads (standalone)

Caliper Caliper (standalone)

Rotor and padtemperaturessignificantlycooler with CFDconvection

Peak

temperaturessimilar

Calipertemperaturessomewhatwarmer


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Thermal Results

Temperature around circumference of rotor contact face

295

300

305

310

315

320

Elem 45600 Elem 46938 Elem 47322 Elem 45822 Elem 46991 Elem 46213 Elem 45341

Tem

perature(degC)

Standalone (RadTherm convection) Reference temp (CFD convection)

Small variation around rotor in bothcases

Convection approach has significantimpact on average


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Thermal Results (CFD convection)


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Comparison of Convection Methods

Part aver age temperatures

220

240

260

280

300

320

340

775 825 875 925 975

Time (s)

Temperature(degC)

Rotor contact face (inboard) (standalone)

Rotor contact face (inboard) (local CFD convection)

Rotor contact face (inboard) (part-averaged CFD convection)

Part-averaged CFD convection resultssimilar to local convection results

Variation around rotor face is slightlylarger with local CFD but relatively small

Temperature around circumference of rotor contact face

290

295

300

305

310

315

320

Elem

45600

Elem

46938

Elem

47322

Elem

45822

Elem

46991

Elem

46213

Elem

45341

Temperature(degC)

Standalone (RadTherm convection)

Reference temp (CFD convection)

Reference temp (part-averaged CFD convection)


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Comparison of Convection Methods:

Average convection flux Part convection fluxes very similar between localCFD and part-average CFD

Part convection flux

-16000

-14000

-12000

-10000

-8000

-6000

-4000

-2000

0

2000

75 275 475 675 875

Time (s)

Netconvectionflux(W/m^2)

Caliper (part-average CFD)

Caliper (local CFD)

Rotor (part-average CFD)

Rotor (local CFD)

Rotor contact face (part-average

CFD)

Rotor contact face (local CFD)


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Simulation performance comparison

CFD Runtime

(12 processors)

Thermal Runtime

(1 processor)

Total

Standalone

(RadTherm

convection)

0 2 hours 2 hours

Reference-

temperature CFD

convection

66 hours 2 hours 68 hours

(2.8 days)

Fully coupled

CFD convection

(estimated)

175 hours 14 hours 189 hours

(7.9 days)


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Coupling of results to FEA model

Temperature results from solid and shellelements can be exported to FEA tools for

structural analysis including heat loads /thermal stresses

Abaqus .odb file (RadTherm v11.0)

Nastran file with temperatures at vertices (otherFEA codes)

Mesh similar to or same as thermal model

could be used Mixed shell/solid hexa & tetra


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Validation of standalone thermal model

Rotor Face

Rotor Edge

Hub

Adapter

Bearing RaceAverage

Peak (C)

Average

Trough (C)

Sim 736 631

Test 716 648

Difference 20 -17

Sim 649 622

Test 653 642

Difference -4 -20

Final (C)

Sim 332

Test 290

Difference 42

Sim 138

Test 136

Difference -2

TC1&3

TC 2

TC4

TC5


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Conclusions

One-way reference-temperature based CFDcoupling shown to be

effective at capturingdetailed flow effects

Efficiency is improvedcompared to full coupling,

although lower thanstandalone model

Choice of convectionmethod and couplingapproach will be dictatedby needs of specificanalysis

brake analysis-temperature approach

Documents

cfd model

typicalcaliper temperature

brake parts

typical rotor temperature

thermal analysis

cfd resultsafter

effectivelyuse cfd

cfd casesper