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

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)

Context Stack FGR Fresh Air Inlet FD FAN Fresh Air + FGR Duct to STRONG Steam out Burner VIBRATION (heating) MAX Boiler REACHABLE LOAD ≈ 50 % Burner STAR Global Conference 2013 March 18-19 2013 2

Context  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! STAR Global Conference 2013 March 18-19 2013 3

Context From FD FAN Upstairs  Fan to burner ductwork subject to severe space limitation  Air flow probably not optimal  Although evaluated as acceptable, ductwork must be investigated To Burner & Boiler STAR Global Conference 2013 March 18-19 2013 4

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 5

Context STAR Global Conference 2013 March 18-19 2013 6

Problem Analysis 8 sec 9 sec 10 sec 11 sec 12 sec 23 pulsations in 4 seconds = 5.75 Hz STAR Global Conference 2013 March 18-19 2013 7

Problem Analysis Possible causes:  Problematic fan > 1500 rpm  Unstable flame in boiler Vibration present EVEN without combustion  Tube bank resonant frequency  Aerodynamics in ducts STAR Global Conference 2013 March 18-19 2013 8

Problem Analysis FD Fan 4½ x 3½ ft 4½ x 6 ft Burner/ Boiler 37 𝑔𝑢/𝑡 22 𝑔𝑢/𝑡 5.75 𝐼𝑨 = 6.4 𝑔𝑢 5.75 𝐼𝑨 = 3.8 ft @ 50 % LOAD : STAR Global Conference 2013 March 18-19 2013 9

Problem Analysis Suspect: Eddies detaching 5.75 times per second STAR Global Conference 2013 March 18-19 2013 10

CFD Analysis - GEOMETRY Velocity Inlet : Uniform profile Expansion joint Air/FGR duct Sharp elbow Windbox Burner Flow split outlet after burner STAR Global Conference 2013 March 18-19 2013 11

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 12

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 13

CFD Analysis – RESULTS BASE CASE STEADY STATE 50% LOAD : STAR Global Conference 2013 March 18-19 2013 14

CFD Analysis – RESULTS BASE CASE STEADY STATE 50% LOAD : STAR Global Conference 2013 March 18-19 2013 15

CFD Analysis – RESULTS BASE CASE STEADY STATE 50% LOAD : STAR Global Conference 2013 March 18-19 2013 16

CFD Analysis – RESULTS BASE CASE STEADY STATE 50% LOAD : STAR Global Conference 2013 March 18-19 2013 17

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 18

CFD Analysis – PHYSICS TRANSIENT  Code: STAR-CCM+ 7.04.006  Fluid flow: transient 𝟐 𝟔.𝟖𝟔𝑰𝒜∗𝟐𝟏 = 17 ms  Time step : 1/10 th of one expected cycle = 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 19

CFD Analysis – RESULTS TRANSIENT  Base Case 50 % LOAD 10.5 Static Pressure 10.3 [in H2O] 10.1 9.9 9.7 9.5 0 1 2 3 4 5 6 7 8 9 10 Time [sec.] STAR Global Conference 2013 March 18-19 2013 20

CFD Analysis – RESULTS TRANSIENT  Base Case 100 % LOAD Static Pressure 35 34.5 [in H2O] 34 33.5 33 32.5 32 0 1 2 3 4 5 6 7 8 9 10 Time [sec.] STAR Global Conference 2013 March 18-19 2013 21

CFD Analysis – RESULTS TRANSIENT  Base Case 100 % LOAD Amplitude: ± 1 in w.c. Pulsation: 4-5 Hz 50 % LOAD Amplitude: ± 0.25 in w.c. Pulsation: 2-3 Hz STAR Global Conference 2013 March 18-19 2013 22

CFD Analysis – RESULTS TRANSIENT  Base Case Duct side wall  5 ft x 10 ft 100 % LOAD 520 lbs Force Amplitude: ± 1 in w.c. Pulsation: 4-5 Hz Enough to make duct side wall move! 50 % LOAD Amplitude: ± 0.25 in w.c. 130 lbs Force Pulsation: 2-3 Hz STAR Global Conference 2013 March 18-19 2013 23

CFD Analysis – SOLUTION GOAL: Stabilize the flow Must break the detaching eddies OPTIONS: Expensive and not possible given  Re-design ducting constrained schedule  Install turning vanes  Solution tried:  1 Turning vane  2 Turning vanes  3 Turning vanes  3 Turning vanes + perforated plate at windbox inlet STAR Global Conference 2013 March 18-19 2013 24

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 25

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 26

CFD Analysis – RESULTS SOLUTION STEADY STATE 50 % LOAD : STAR Global Conference 2013 March 18-19 2013 27

CFD Analysis – RESULTS SOLUTION STEADY STATE 50% LOAD : STAR Global Conference 2013 March 18-19 2013 28

CFD Analysis – RESULTS SOLUTION STEADY STATE 50 % LOAD : STAR Global Conference 2013 March 18-19 2013 29

CFD Analysis – RESULTS SOLUTION STEADY STATE 50 % LOAD : STAR Global Conference 2013 March 18-19 2013 30

CFD Analysis – RESULTS SOLUTION  TRANSIENT, 50 % LOAD: 10.5 Static Pressure [in 10.3 10.1 H2O] 9.9 9.7 9.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Time [sec.] STAR Global Conference 2013 March 18-19 2013 31

CFD Analysis – RESULTS SOLUTION  TRANSIENT, 100 % LOAD: Static Pressure 35 34 [in H2O] 33 32 31 30 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Time [sec.] STAR Global Conference 2013 March 18-19 2013 32

CFD Analysis – RESULTS SOLUTION  TRANSIENT 100 % LOAD Amplitude: ± 0.05 in w.c. (20X smaller) Pulsation: NONE Base Case Solution 50 % LOAD Amplitude: ± 0.025 in w.c. (10X smaller) Pulsation: NONE STAR Global Conference 2013 March 18-19 2013 33

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 34

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 35

Conclusions  Total Turnaround time between 1 st phone call, CFD study and recommendations: 2 weeks STAR Global Conference 2013 March 18-19 2013 36

Hardware 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 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 Transient, 10 sec., Base Case 553 819 40 000 236 h 6 h 9 min 0.005 sec. time step, 20 iter/step Transient, 10 sec., Solution 5 553 494 40 000 1 553 h 38 h 55 min 0.005 sec. time step, 20 iter/step STAR Global Conference 2013 March 18-19 2013 37