Emission and smoke recirculation in road tunnels (FGU2008/007_OBF)
Overview
Background & policy context:
To quantify emission and smoke recirculation in road tunnels very few established guidelines are available. Nowadays arrangements to reduce recirculation are decided upon rudimentarily specifications and knowledge.
The planned research work aims to extensively investigate recirculation in road tunnels. The results should be used in the future as a basis for the design of new and existing tunnel ventilation systems (new guidelines).
The main part of the research covers a systematic analysis of the factors of influence regarding recirculation (e.g. jet velocity, height of the chimney, portal situation, wind) using CFD- Simulations. The simulations will be validated with in situ measurements on existing road tunnels. The measurements will be carried out using the well-proven tracer gas method by an accredited laboratory. On the basis of the simulation and measurement results, a method to quantify will be developed. A further part is to define appropriate requirements and recommendations as well as documentation.
Objectives:
The principal objective of the research is to create a comprehensive basis for a better understanding of emissions and smoke recirculation in road tunnels with and without ventilation systems. The primary aim of the research would be:
- Evaluation of the risk potential (in what way is recirculation a problem, what are the hazards?).
- Creation of fundamental knowledge regarding emission and smoke recirculation.
- Development of a method to evaluate emission and smoke recirculation and arrangements for new and existing road tunnels. The method considers all the relevant aspects, such as height of the chimney, jet velocity, etc.
- Definition of recommendations, requirements and possibilities to compensate (What are the requirements? How much recirculation is allowed? What are the arrangements to achieve the requirements?)
- Publication of the results on national or international environment (journals, conferences).
The research project aims primary to eliminate the uncertain, inaccurate or missing basis in the field of emission and smoke recirculation. That can result in considerable cost and time savings during the design and realisation.
Methodology:
The following stages are planned for the project:
Part 1: Development of the foundations / hazard potential
The first part is on the one hand a literature review on the other hand a theoretical and practical considerations of circulation bypasses of existing tunnels.
The literature already available development / research approaches used (eg. guidelines) to be collected, analysed and assessed and common practice. Based on theoretical and practical considerations to flow short circuits and related aspects (eg. structural measures, methods) to analyse and describe.
The potential risk for tunnel users, emanating from short circuits of smoke or pollutants should be examined by a risk analysis.
Part 2: Parameters of the recirculation
The second part comprises primarily the detailed analysis of the various influencing factors regarding the smoke and pollutants shorts. The various influencing factors (chimney height, distance Fireplace - Portal, blow-off, wind conditions, site situation, etc.) are examined systematically using detailed CFD simulations. The simulations should show relevant factors that must be considered in the design of tunnel ventilation. In addition to the factors influencing new tunnels should be identified on the basis of simulations additional opportunities that can improve the safety situation as regards the recirculation of tunnel users in existing tunnels without major structural measures. This can be, for example, the incorporation of diaphragms for increasing the blow-off speed or a suitable ventilation control.
The CFD simulations provide various parameters by which the recirculation of smoke and pollutants can be influenced and their dependence on one another. The factors are based on various criteria (new tunnel system - rehabilitation of existing plant, necessary structural adjustments, non-controllable environmental factors, etc.). The aim is an approach to avoid flow short circuits are achieved.
Part 3: Validation and Review
Some of the performed CFD simulations are to be validated by measuring the flow shorts to existing tunnels. The measurements are performed using proven Tracer gas method.
Part 4: Definition of guidelines / recommendations
The CFD simulations and validation by measurements intended to provide a guide and a procedure for the design of new and existing tunnels. The influencing parameters should be defined and classified according to thei
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