[PPT] - Duct Pulsation Problem Captured and Solved Using STAR-CCM+ Eric PowerPoint Presentation

SLIDE 1

Duct Pulsation Problem Captured and Solved Using STAR-CCM+

Eric Duplain, Eng., M.Eng. (BMA) François McKenty, Eng., Ph.D. (BMA) Normand Brais, Eng., Ph.D. (BMA) John Viskup, President (Victory Energy)

SLIDE 2

2

Context

Steam out (heating) FGR FD FAN Fresh Air Inlet Boiler Burner Fresh Air + FGR Duct to Burner Stack STRONG VIBRATION MAX REACHABLE LOAD ≈ 50 %

STAR Global Conference 2013 March 18-19 2013

SLIDE 3

3

 Less than two months left before heating season starts – MUST WORK!  Fan to burner ductwork evaluated by burner manufacturer as

acceptable

 Turnaround time: two weeks!

Context

STAR Global Conference 2013 March 18-19 2013

SLIDE 4

4

 Fan to burner ductwork subject

to severe space limitation

 Air flow probably not optimal  Although evaluated as

acceptable, ductwork must be investigated

Context

From FD FAN Upstairs To Burner & Boiler

STAR Global Conference 2013 March 18-19 2013

SLIDE 5

5

Context "Gregg, I took this video with my phone. The floor is shaking and it's hard to hold still. Near the end I moved the phone over to a floor mounted brace to steady the phone. You can still see the housing moving when comparing to the concrete motor base.” End-Customer

STAR Global Conference 2013 March 18-19 2013

SLIDE 6

6

Context

STAR Global Conference 2013 March 18-19 2013

SLIDE 7

7

Problem Analysis

23 pulsations in 4 seconds = 5.75 Hz

8 sec 9 sec 10 sec 11 sec 12 sec STAR Global Conference 2013 March 18-19 2013

SLIDE 8

8

Problem Analysis Possible causes:

 Problematic fan  Unstable flame in boiler  Tube bank resonant frequency  Aerodynamics in ducts

> 1500 rpm Vibration present EVEN without combustion

STAR Global Conference 2013 March 18-19 2013

SLIDE 9

9

Problem Analysis

4½ x 6 ft FD Fan Burner/ Boiler 4½ x 3½ ft

37 𝑔𝑢/𝑡 5.75 𝐼𝑨 = 6.4 𝑔𝑢 22 𝑔𝑢/𝑡 5.75 𝐼𝑨 = 3.8 ft

@ 50 % LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 10

10

Problem Analysis

Suspect: Eddies detaching 5.75 times per second

STAR Global Conference 2013 March 18-19 2013

SLIDE 11

11

CFD Analysis - GEOMETRY

Sharp elbow Windbox Velocity Inlet : Uniform profile Air/FGR duct Expansion joint Flow split outlet after burner Burner

STAR Global Conference 2013 March 18-19 2013

SLIDE 12

12

CFD Analysis - MESH

 Polyhedral mesh  Base size 5 cm ( 2 in)  3 prism layer, thickness 6 mm ( ¼ in)  550k cells

STAR Global Conference 2013 March 18-19 2013

SLIDE 13

13

CFD Analysis – PHYSICS STEADY STATE

 Code: STAR-CCM+ 7.04.006  Fluid flow: steady state  Turbulence: k- model (Two-layer all y+ wall treatment)  Species: air with corrected density for FGR & temperature  Operating condition: 50 % LOAD  Porous media to simulate burner effect on flow

STAR Global Conference 2013 March 18-19 2013

SLIDE 14

14

CFD Analysis – RESULTS BASE CASE

STEADY STATE 50% LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 15

15

CFD Analysis – RESULTS BASE CASE

STEADY STATE 50% LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 16

16

CFD Analysis – RESULTS BASE CASE

STEADY STATE 50% LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 17

17

CFD Analysis – RESULTS BASE CASE

STEADY STATE 50% LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 18

18

CFD Analysis – RESULTS STEADY STATE

 PRELIMINARY CONCLUSIONS:

 Large recirculation after sharp turn  Will surely induce flow instability (turbulence)  High residuals indicate transient phenomenon may be occuring  Must complete analysis with transient CFD run STAR Global Conference 2013 March 18-19 2013

SLIDE 19

19

CFD Analysis – PHYSICS TRANSIENT

 Code: STAR-CCM+ 7.04.006  Fluid flow: transient

 Time step : 1/10th of one expected cycle =

𝟐 𝟔.𝟖𝟔𝑰𝒜∗𝟐𝟏 = 17 ms

5 ms chosen for safety (given time constraint)

 Total time: up to 10 sec.

 Turbulence: k- model (Two-layer all y+ wall treatment)  Species: Air with corrected density for FGR & temperature  Operating conditions: 50 %, 100 % LOADS  Porous media to simulate burner effect on flow

STAR Global Conference 2013 March 18-19 2013

SLIDE 20

20

CFD Analysis – RESULTS TRANSIENT

 Base Case 50 % LOAD

9.5 9.7 9.9 10.1 10.3 10.5 1 2 3 4 5 6 7 8 9 10 Static Pressure [in H2O] Time [sec.]

STAR Global Conference 2013 March 18-19 2013

SLIDE 21

21

CFD Analysis – RESULTS TRANSIENT

 Base Case 100 % LOAD

32 32.5 33 33.5 34 34.5 35 1 2 3 4 5 6 7 8 9 10 Static Pressure [in H2O] Time [sec.]

STAR Global Conference 2013 March 18-19 2013

SLIDE 22

22

CFD Analysis – RESULTS TRANSIENT

 Base Case

100 % LOAD

Amplitude: ± 1 in w.c. Pulsation: 4-5 Hz Amplitude: ± 0.25 in w.c. Pulsation: 2-3 Hz

50 % LOAD

STAR Global Conference 2013 March 18-19 2013

SLIDE 23

23

CFD Analysis – RESULTS TRANSIENT

 Base Case

Duct side wall  5 ft x 10 ft 520 lbs Force 130 lbs Force

Enough to make duct side wall move!

Amplitude: ± 0.25 in w.c. Pulsation: 2-3 Hz

50 % LOAD 100 % LOAD

Amplitude: ± 1 in w.c. Pulsation: 4-5 Hz

STAR Global Conference 2013 March 18-19 2013

SLIDE 24

24

CFD Analysis – SOLUTION

GOAL: Stabilize the flow Must break the detaching eddies OPTIONS:

 Re-design ducting  Install turning vanes  Solution tried:

 1 Turning vane  2 Turning vanes  3 Turning vanes  3 Turning vanes + perforated plate at windbox inlet

Expensive and not possible given constrained schedule

STAR Global Conference 2013 March 18-19 2013

SLIDE 25

25

CFD Analysis – SOLUTION

 3 turning vanes + perforated plate at burner inlet

Perforated plate 1 in , 1.25 in C-C, staggered 2 in w.c. P @ FULL LOAD 3 turning vanes

STAR Global Conference 2013 March 18-19 2013

SLIDE 26

26

CFD Analysis – MESH SOLUTION

 Polyhedral mesh  Base size 4.5 cm (1¾ in)  Turning vanes 2.25 cm (0.9 in),  Perforated plate 6 mm (¼ in)  5.5M cells (10X base case) STAR Global Conference 2013 March 18-19 2013

SLIDE 27

27

CFD Analysis – RESULTS SOLUTION

STEADY STATE 50 % LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 28

28

CFD Analysis – RESULTS SOLUTION

STEADY STATE 50% LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 29

29

CFD Analysis – RESULTS SOLUTION

STEADY STATE 50 % LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 30

30

CFD Analysis – RESULTS SOLUTION

STEADY STATE 50 % LOAD :

STAR Global Conference 2013 March 18-19 2013

SLIDE 31

31

CFD Analysis – RESULTS SOLUTION

 TRANSIENT, 50 % LOAD:

9.5 9.7 9.9 10.1 10.3 10.5 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Static Pressure [in H2O] Time [sec.]

STAR Global Conference 2013 March 18-19 2013

SLIDE 32

32

CFD Analysis – RESULTS SOLUTION

 TRANSIENT, 100 % LOAD:

30 31 32 33 34 35 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Static Pressure [in H2O] Time [sec.]

STAR Global Conference 2013 March 18-19 2013

SLIDE 33

33

CFD Analysis – RESULTS SOLUTION

 TRANSIENT

100 % LOAD

Amplitude: ± 0.05 in w.c. (20X smaller) Pulsation: NONE Amplitude: ± 0.025 in w.c. (10X smaller) Pulsation: NONE

50 % LOAD

Base Case Solution

STAR Global Conference 2013 March 18-19 2013

SLIDE 34

34

CFD Analysis – RESULTS TRANSIENT

 Two weeks after initial email: satisfactory solution!  Drawings of perforated plate and turning vanes prepared and sent  Installation of parts started two days later  Boiler started: 100% LOAD reached… without pulsation!  Problem Solved  End Customer Happy

STAR Global Conference 2013 March 18-19 2013

SLIDE 35

35

Conclusions

 Although ductwork was supplied by a third party, Victory Energy

hired BMA to conduct CFD analysis

 Air flow instability indicated by steady state CFD runs  Pulsation phenomenon captured using transient CFD runs  2-5 Hz simulated vs. 5.75 Hz measured, close enough given that:

 Incomplete geometry provided  Exact load around 50 % but unknown

 Proposed solution: turning vanes and perforated plate  Pulsation phenomenon eliminated for all simulated loads

STAR Global Conference 2013 March 18-19 2013

SLIDE 36

36

Conclusions

 Total Turnaround time between 1st phone call, CFD study and

recommendations: 2 weeks

STAR Global Conference 2013 March 18-19 2013

SLIDE 37

37

Hardware

Computing Time

Description Type # poly cells Iter CPU time Elapsed time Base Case Steady State 553 819 1 000 5 h 54 min 9 min Solution Steady State 5 553 494 1 000 38 h 50 min 58 min Base Case Transient, 10 sec., 0.005 sec. time step, 20 iter/step 553 819 40 000 236 h 6 h 9 min Solution Transient, 10 sec., 0.005 sec. time step, 20 iter/step 5 553 494 40 000 1 553 h 38 h 55 min

Machines

Operating System Linux 3.0.26-0.7-default (SUSE Enterprise Server 11) CPU Type Intel(R) Xeon(R) CPU E5-1620 0 @ 3.60GHz (x86_64) CPU Addressability 64 bit CPU Count 4 (4 cores/socket, Hyper-threading) CPU Cache 10 240 KB (L2) Physical Memory 15 926 MB 10 machines x 4 cores/machine 40 cores total Network 1 Gb Ethernet

STAR Global Conference 2013 March 18-19 2013