Reflection properties of a flow pipe with a small angle diffuser outlet
2010 (English)In: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 1, 2010, 706-712 p.Conference paper (Refereed)
The reflection of plane acoustic waves is studied for an open pipe termination where the outlet section about 10 cm long is a diffuser with a small angle. Diffuser angles up to 6o with a sharp outlet edge are considered both without and with a mean flow. The experiments are performed for Helmholtz numbers, He, based on the pipe diameter, up to 1.0 and mean flow Mach numbers, M, up to 0.25. A multi-microphone method is used for accurate measurements of the acoustic fields inside the pipe. With no mean flow, the reflection coefficient results are compared with the theories for thin walls by Levine and Schwinger  and for the end correction and thick walls by Ando , respectively. The data for the magnitude of the reflection coefficient for different pipe end geometries show that in the low frequency regime it is the outlet radius that determines the magnitude of the energy reflection coefficient. The same collapse in the data is not obtained for the end correction which is strongly affected by the pipe end geometry. Experimental results of the reflection coefficient in the presence of a mean flow show a similar behaviour as without flow. However, it is the Strouhal number of the outlet that governs the losses, i.e., radiation and flow losses. For a region of small Strouhal numbers, the reflection is larger than one, as predicted for straight pipes, [3, 4]. An increased diffuser angle and rounded edges both increase the reflection at the pipe termination in a critical range of Strouhal numbers, which indicates that the reflection coefficient is strongly dependent on the shape, half angle, and edge curvature of the pipe end in this region.
Place, publisher, year, edition, pages
2010. 706-712 p.
Accurate measurement, Diffuser angle, Energy reflection coefficients, Flow loss, Frequency regimes, Helmholtz number, Mean flow, Pipe diameter, Plane acoustic waves, Reflection properties, Rounded edge, Straight pipe, Thick-wall, Thin walls, Acoustic fields, Ducted fan engines, Mach number, Strouhal number, Reflection
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-148938ScopusID: 2-s2.0-84871429065ISBN: 978-161782255-1OAI: oai:DiVA.org:kth-148938DiVA: diva2:738013
17th International Congress on Sound and Vibration 2010, ICSV 2010, 18 July 2010 through 22 July 2010, Cairo, Egypt
QC 201408152014-08-152014-08-142016-09-20Bibliographically approved