The treatment of the throttling effect in incompressible 1D flow solvers. Gary Clark & Keith Meeks Atkins, UK Thomas Wicht HBI Haerter, Switzerland

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1 The treatment of the throttling effect in incompressible 1D flow solvers Conor Fleming Atkins, UK Gary Clark & Keith Meeks Atkins, UK Thomas Wicht HBI Haerter, Switzerland

2 The throttling effect of a tunnel fire Fire increases the aerodynamic resistance of the tunnel Important for ventilation system design Various treatments in different software packages Limited literature available Objectives identify mechanisms of throttling effect understand how they are modelled

3 Outline Overview of throttling effect Consider some throttling mechanisms Wall friction & local losses Momentum change at fire Demonstration User-defined fire pressure drop (IDA Tunnel 1.1)

4 Tunnel fire Longitudinal ventilation system Self-rescue Fire-fighting fan thrust smoke evacuation

5 Ventilation system design Achieve critical velocity Overcome aerodynamic resistance, e.g: buoyancy vehicle drag wall friction & local losses momentum change portal pressure difference Iterative numerical method fan thrust evacuation smoke

6 System resistance Some losses are temperature-dependent fan thrust critical velocity heat release rate

7 System resistance Some losses are temperature-dependent increased fan thrust same critical velocity increased heat release rate

8 System resistance Some losses are temperature-dependent buoyancy wall friction & local losses momentum change increased fan thrust same critical velocity increased heat release rate

9 Wall friction & local losses hot Losses depend on dynamic pressure Δp friction = λl D 1 2 ρu2 Δp exit = K exit 1 2 ρu2 Dynamic pressure is proportional to temperature 1 2 ρu2 T Flow is compressible!

10 Wall friction & local losses cold hot Ideal Gas Law ρ = p RT T c ρ h = ρ c T h Continuity m = ρua = const. u 2 h = u2 T 2 h c 2 T c Corrected dynamic pressure 1 2 ρ hu h 2 = 1 2 ρ cu c 2 T h T c

11 Wall friction & local losses cold hot Pressure losses now expressed in terms of known variables, ρ c, u c, T h Δp friction = λl D 1 2 ρ cu c 2 T h T c Δp exit = K exit 1 2 ρ cu c 2 T h T c

12 Pressure loss at fire Momentum change (Hwang & Chaiken, 1978) u c 1D control volume u h ΣF CV = m u c u h ρ c T c ρ h T h u h = u c T h T c Δp fire = ρ c u c 2 1 T h T c HC78

13 Pressure loss at fire Empirical formula via 3D CFD (Dutrieue & Jacques, 2006) u c Control volume Δp fire = Q fire 0.8 u c 1.5 D 1.5 C DJ06 Q fire

14 Implementation Some flow solvers require user input e.g. IDA Tunnel general fire pressure loss C fire = Δp fire Q fire Proposed use of IDA Tunnel 1. Calculate Δp fire manually Δp = 0 HC78 or DJ06 2. Calculate C fire manually Input to IDA Tunnel 3. IDA Tunnel simulation Solve for u c, T h

15 Implementation Some flow solvers require user input e.g. IDA Tunnel general fire pressure loss C fire = Δp fire Q fire Some flow solvers do not require user input e.g. SES v4.1 solves HC78 momentum change Proposed use of IDA Tunnel 1. Calculate Δp fire manually Δp = 0 HC78 or DJ06 2. Calculate C fire manually Input to IDA Tunnel 3. IDA Tunnel simulation Solve for u c, T h

16 Demonstration Trivial case Verify agreement of IDA Tunnel 1.1 and SES v4.1 verify jet fan verify wall friction

17 Demonstration Trivial case Verify agreement of IDA Tunnel 1.1 and SES v4.1 verify jet fan verify wall friction Results Good agreement Solver u [m/s] Δp 0 [Pa] IDA Tunnel SES v

18 Demonstration Fire pressure loss in IDA Tunnel Test models Δp fire = 0 Pa Δp fire = DJ06 (empirical) Δp fire = HC78 (momentum change) Vary fire size Q fire = 20 MW

19 Demonstration Assumptions (to isolate fire pressure drop) No wall heat transfer No entry/exit loss Q fire = 20 MW

20 Demonstration - pressure

21 Demonstration - velocity

22 Demonstration - temperature

23 Demonstration vary fire size

24 Conclusions Overview of throttling effect Focussed on wall friction & local losses momentum change Suggested method for user-defined momentum change Demonstrated method using IDA Tunnel

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THE TREATMENT OF THE THROTTLING EFFECT IN INCOMPRESSIBLE 1D FLOW SOLVERS

- 141 - THE TREATMENT OF THE THROTTLING EFFECT IN INCOMPRESSIBLE 1D FLOW SOLVERS C. Fleming, G. Clark, K. Meeks; Atkins Ltd, UK T. Wicht; HBI Haerter, Switzerland ABSTRACT This paper is concerned with