Transient Response of Nozzels and Diffusors in Pressure-Duct Systems

摘要

This paper attempts to investigate the behavior of pressure waves through nozzels anddiffusors in pressure duct systems. It presents the results of some recent studies in whichthe extent of transmission and reflection of pressure waves of specific throttle types wereinvestigated. In fact there is an unsteady difference between quasi-steady calculationsand the real physical behavior during a pressure wave passage. In order to ascertain theinfluence of a conical throttle (orifice/pipe cross-section area ratio of 1:8) – used once asa nozzle and on the other side as a diffusor - on the transmission of pressure waves, 2arrangements with steel pipe models ( “Straight pipe” and “T-junction”) were conductedin which this throttle element was tested with single pressure waves. For comparison andalso for practical use, the results of the experimental investigations are depicted, afterelimination of additional physical influences, in the form of transmission factors indiagrams. Furthermore, a suitable mathematical approach for computation of thetransmisson behavior is developed. The suitability of application for this unsteadythrottle headloss in the usual unsteady calculation is verified by a standard characteristicmethod (MOC) using control calculations of the experiments. In this unsteady headlossapproach the prehistory of the incident pressure wave is included. Influences of basicflow conditions of the transmission- and reflection behavior are also be described andevaluated.