Analysis of Buoyancy-Driven Flow Through Openings in Compartment Fires - The Use of Reduced-Scale Experiments for CFD Validation and Numerical Investigation: The Use of Reduced-Scale Experiments for CFD Validation and Numerical Investigation
Author
Larsen, Lukas Højer
Term
4. term
Publication year
2026
Abstract
This thesis investigates buoyancy-driven flow through a naturally ventilated compartment opening by combining reduced-scale fire experiments and numerical simulations. A 1:5 reduced-scale ISO 9705 compartment was constructed, and experiments used a propane-fueled burner with a target heat release rate of 50 kW. Gas temperatures inside the compartment, opening temperatures, and velocities at the opening were measured to characterize flow and thermal stratification, and two repetitions assessed repeatability. The configuration was then replicated in Fire Dynamics Simulator (FDS) to study the influence of numerical choices (including grid resolution and turbulence treatment) and to compare with measurements. The comparison indicated that FDS generally reproduced the overall flow structure and the neutral plane location, but typically underpredicted temperatures and velocities. Buoyancy-based scaling was examined by comparing the reduced-scale results to a corresponding full-scale model; Froude scaling reproduced the general flow structure and stratification, while quantitative differences remained, highlighting limitations of partial scaling. The work provides insight into the use of reduced-scale experiments for CFD validation and into modeling considerations for naturally ventilated compartment fires.
Dette speciale undersøger opdriftsdrevet strømning gennem en åbning i en naturligt ventileret rumbrand ved at kombinere reducerede modellforsøg og numeriske simuleringer. En 1:5 ISO 9705-kompartment blev opbygget, og forsøgene brugte en propanbrænder med en målsat varmefrigivelsesrate på 50 kW. Gastemperaturer i rummet, åbningstemperaturer og hastigheder i åbningen blev målt for at karakterisere strømningen og den termiske lagdeling, og to gentagelser blev udført for at vurdere reproducerbarhed. Opsætningen blev efterfølgende replikeret i Fire Dynamics Simulator (FDS) for at undersøge indflydelsen af numeriske valg (herunder maskeopløsning og turbulensbehandling) og for at sammenholde resultaterne med måledata. Sammenligningen viste, at FDS generelt genskabte den overordnede strømningsstruktur og neutralplanens placering, men typisk underestimerede temperaturer og hastigheder. Skaleringsrelationer for opdrift blev undersøgt ved at sammenligne den reducerede model med en tilsvarende fuldskalamodel; Froude-skalering genskabte de generelle strømningstræk og den termiske lagdeling, men kvantitative forskelle bestod, hvilket illustrerer begrænsningerne ved delvis skalering. Arbejdet giver dermed indsigt i brugen af reducerede skala-forsøg til validering af CFD og i modelleringsmæssige overvejelser for naturligt ventilerede rumbrande.
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