Abstract
The influence of a perforated extension region on pressures radiated from the end of a duct is studied numerically using CFD. Planar 2-D geometry is considered and particular attention is paid to the case of pressure disturbances radiated from railway tunnels in cut-and-cover regions. The mechanism that causes this behaviour is described and it is shown to have an important influence of the effectiveness of a perforated extension region. It is found that such regions can strongly reduce the pressures radiated from a duct outlet, but that this benefit is offset by pressures radiated directly from the holes along the perforated region itself. In the particular case of tunnel design, practical studies of wave transmission are usually based on 1-D, plane-wave, analyses. Accordingly, attention is paid to assessing the limitations of such approaches in the case of wave propagation along a perforated region.
Highlights
When a pressure wave travelling along a duct reaches an open outlet end, the principal consequence is a reflection process that causes a new wave to propagate back along the duct
This paper focuses on the particular case of a railway tunnel portal at the end of a cut-and-cover region
The use of a long, perforated extension region to reduce the amplitudes of micro-pressure waves (MPWs) emitted from an open end of a duct has been investigated using a 2-D CFD analysis
Summary
When a pressure wave travelling along a duct reaches an open outlet end, the principal consequence is a reflection process that causes a new wave to propagate back along the duct. The most commonly cited exception occurs when a high speed train enters a slab-track tunnel of moderate length In such cases, the pressure wave generated by nose-entry steepens as it propagates along the tunnel and can become almost a shock wave before reaching the exit portal. The most common counter-measure to prevent the occurrence of unacceptable MPWs is the building of special entrance regions for tunnels [6,7,8,9] The purpose of these is to elongate the nose-entry wavefront sufficiently to ensure that, even after steepening during propagation along the tunnel, it is not too steep when it reaches the exit portal. In addition to drawing general conclusions from the work, the opportunity is taken to assess briefly the capability of 1-D methods to model the reflection process inside the tunnel
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
