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
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