The Froude-number based reduced-scale modeling is a technique commonly used to investigate the flow of heat and mass in building fires. The root of the method is the thermodynamic model of a flow in a compartment and several non-dimensional flow numbers based on the proportionalities of the Navier-Stokes and heat transfer equations. The ratio of inertial forces to the buoyancy forces, known as the Froude-number, plays a pivotal role within these proportionalities. This paper is an attempt to define the range of credible scale modeling using the Froude-number. We verify the credibility of the modeling by small fire (approximately 150 kW) in a small compartment, comparing data from a physical test (scale 1:1 and 1:4) and the numerical model’s data (Fire Dynamics Simulator, scales 1:1, 1:2, 1:4, 1:10, 1:20, and 1:50). The scope of the research covers a wide range of fires, with observed change of the flow from turbulent to laminar. The results show that the applicability of Froude-number reduced-scale modeling has limitations related to the scale. Therefore, it should be applied with care following sensibility analysis. We propose a method for sensibility analysis using Computational Fluid Dynamics (CFD) modeling.

A common method for investigating various fire- and smoke-related phenoma is a reduced-scale fire modelling that uses the conservation concept of Froude number as its primary similarity criterion. Smoke obscuration measurements were not commonly used in this approach. In this paper, we propose a new type of optical densitometer that allows for smoke obscuration density measurements on a reduced-scale. This device uses a set of mirrors to increase the optical path length, so that the device may follow the geometrical scale of the model, but that still measures smoke obscuration as if it were in full scale. The principle of operation is based on the Bougher-Lambert-Beer law, with modifications related to the Froude number-based scaling principles, to streamline the measurements. The proposed low-budget (< $1000) device was built, calibrated with a set of the reference optical filters, and used in a series of full- (1:1) and reduced-scale (1:4) experiments with n-Heptane fires in a small compartment. The main limitation of this study is the assumption that there is similar soot production in full- and reduced-scale fires, which may not be true for many Froude-number scaling applications. Therefore, it must be investigated in a case-by-case basis. In our case, the results are promising. The measured obscuration in the reduced-scale had a 10% error versus averaged measurements in full-scale measurements. Moreover, there were well represented transient changes of the smoke layer optical density during the combustion and after the smoke layer settled.

Positioning the positive pressure ventilator in front of the door opening affects the effectiveness of the rescue operation carried out during a fire. An important factor determining the effectiveness of the positive pressure ventilator is also the layout of the rooms within the gas exchange path and the obstacles present there. The purpose of this article is to assess the feasibility of using analyses such as large eddy simulation (LES) to verify the efficiency of mobile fans under simulation conditions, without the need for time-consuming experimentation (also for complex room volumes of buildings). The article presents a comparative analysis to assess the degree of convergence of flow parameters obtained during an experiment (in a multi-story building) and computational fluid dynamics (CFD) simulations. For volumetric flow rate, convergence was achieved at levels ranging from 0.4% (for 5 m) to 11.5% (1 m), and for pressure values, the differences achieved ranged from 0.6% (5 m) to 30.1% (4 m). This paper demonstrates that the LES model can be used to perform CFD simulations in the area of assessing the performance of a positive pressure ventilator. The article also describes a test methodology for determining the flow parameters of an air stream, which can be used to perform numerical simulations.

Determining the appropriate position of a positive pressure ventilator, where it exhibits the highest efficiency (measured by the achieved volumetric flow rate), can influence the success of rescue operations conducted by fire protection units. The aim of this article is to evaluate the possibility of using LES (Large Eddy Simulation) analyses to verify the positioning parameters of positive pressure ventilators in numerical simulation conditions, without the need for time-consuming experiments. The article presents a comparative analysis of full-scale experimental studies (conducted on a test setup to assess the velocity profile of the air jet in open flow) and CFD numerical analyses. The analysis confirmed the convergence of the flow rate parameter entering the surface of the door opening model installed on the test setup. Depending on the distance of the ventilator position (1–7 m), a convergence degree ranging from 1.6% to 3.8% was achieved for the volumetric flow rate. This publication demonstrates that the LES model is a suitable tool for effectively determining the working positions of positive pressure ventilators, as defined in real working conditions (open flow). The analysis may serve as a helpful tool for manufacturers of mobile ventilators, who can use the method for the technological testing of their units without conducting time-consuming experiments.

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