INVESTIGATIONS ON SMOKE PROPAGATION WITH LONGITUDINAL VENTILATION BY MEANS OF A MODEL TUNNEL

Transcription

1 INVESTIGATIONS ON SMOKE PROPAGATION WITH LONGITUDINAL VENTILATION BY MEANS OF A MODEL TUNNEL Wilhelm Jessen 1 ; Andreas Klein 2 1 Institute of Aerodynamics Aachen, 2 Institute of Highway Engineering, RWTH Aachen University, Germany 1

2 Outline Motivation Experimental Setup - Model tunnel, jet fans and moving traffic - Modelling of tunnel fires (helium-air mixture) Measurement technique - Particle-image velocimetry (PIV) Results - Smoke propagation with/without congestion - Smoke propagation with piston effect by stopped traffic Summary and outlook 2

3 Motivation Optimization of longitudinal ventilation systems and tunnel design for normal operation and the event of a tunnel fire Development and construction of a model tunnel to investigate flows in a road tunnel Evaluation of ventilation concepts during the planning stage Experimental and numerical investigations considering a variety of parameters with influence to smoke propagation, stratification Processing period 07/ /2016 Supported by Federal Highway Research Institute (BASt) 3

4 Experimental Setup Construction of the model tunnel Scale 1:18, length 12 m Two-lane cross-sections for unidirectional and bidirectional traffic Rectangular or horseshoe profile (RQ26,5t respectively 10,5t acc. RABT 2006) Transparent materials (PMMA, PA) and medium density fiberboard (MDF) 4

5 Experimental Setup Construction of model jet fans Velocity continuously adjustable (u smax = 35 m/s) Impeller diameter 1:1 500 mm 710 mm 900 mm 1:18 28 mm 40 mm 50 mm Influence of traffic Congestion (in case of fire) Moving and stopped traffic - modified slot car system, v cars,max 4-5 m/s Piston effect on smoke propagation 5

6 Experimental Setup Isothermal modelling of tunnel fires Similarity between reality and model: Froude-number (inertia forces to gravitational forces) Fr v M g L M v R g L R v v R M L L R M v R / v M 4.24 L characteristic value of length Isothermal approach using a helium-air mixture (VAUQUELIN [1]): Q: heat release rate Q L L Q M from 0.73 to 2.91 kw (1-4 MW in real scale) Q R M R M 5 2 Q R / Q M [1] Vauquelin, O.: Experimental simulations of fire-induced smoke control in tunnels using an air-helium reduced scale model : Principle, limitations, results and future. Tunnelling and Underground Space Technology 23 (2008)

7 Experimental Setup Helium-air injection into the model tunnel Injection through a circular hole in the road surface, symmetry plane Visualization of the smoke layer by seeding particles (size 1-2 μm) Determination of the smoke propagation velocity by using Particle-Image Velocimetry (PIV) 7

8 Measurement Technique Particle-Image Velocimetry (PIV) Non-intrusive measurement technique Whole-flow-field technique providing instantaneous velocity vector measurements Adding tracer particles to the flow Illumination of particles by pulsating laser Images recorded by synchronized CCD camera Post processing: cross correlation 8

9 Results Influence of congestion in case of fire Horseshoe profile, unidirectional traffic, 2 2 jet fans Reference case (no traffic) vs. congestion of heavy good vehicles (right lane) and passenger cars (left lane) in front of the fire Jet exit velocities u j = 3.7 m/s and u j = 5 m/s Q R = 2 MW PIV in x-y symmetry plane 9

10 Results u j = 3.7 m/s, no congestion, visualization = 2 s Backlayer 10

11 Results u j = 3.7 m/s, no congestion, velocity distribution u abs Time-averaged velocity distributions for different periods Streamlines show development of backlayer 11

12 Results u j = 3.7 m/s, congestion in the tunnel, visualization = 2 s Backlayer 12

13 Results u j = 3.7 m/s, congestion in the tunnel, velocity distribution u abs 13

14 Results u j = 5.0 m/s, congestion in the tunnel, visualization and velocity distribution u abs 14

15 Results Piston effect on smoke propagation (without ventilation) Unidirectional traffic: passenger cars on left lane, 50% HGVs and 50% passenger cars on right lane In smoke propagation direction and opposite the smoke propagation direction Bidirectional traffic: 50% HGVs and 50% cars on both lanes v cars = 1.5 m/s Traffic stopped after 5 circulations, starting the injection PIV in x-y symmetry plane Q R = 2 MW 15

16 Results Piston effect on smoke propagation (without ventilation) Averaged velocity distributions u abs in smoke propagation opposite smoke propagation bidirectional traffic direction before stop 16

17 Summary and Outlook Summary Construction of a model tunnel (1:18) with jet fans and moving traffic Modelling of tunnel fires by using a helium-air mixture Measurement technique: particle-image velocimetry (PIV) Results show development of a backlayer for a jet exit velocity of u j = 3.7 m/s for both investigated cases (with/ without congestion) - more pronounced (faster development) for the congestion case At u j = 5.0 m/s no backlayering occurred for both cases Piston effect on smoke propagation, dependency on the traffic direction Outlook Model tunnel: wide range of experimental investigations possible (validation of numerical studies, investigation of local flow pattern, aerodynamics on tunnel equipment ) 17

18 Thank you for your attention! Dr.-Ing. Wilhelm Jessen Dipl.-Ing. Andreas Klein Institute of Aerodynamics Aachen Institute of Highway Engineering Wüllnerstr. 5a Mies-van-der-Rohe-Str Aachen, Germany Aachen, Germany