Liquid spray processes possess a typical spreading characteristics in an enclosing cavity. Therefore, the transient jet behaviour in a plenum or chamber with non-circular cross section is studied. The investigation is connected to problems in jet and spray processes where the process configuration of the flow needs to be investigated in order to achieve optimum working conditions and consequently to yield higher performance of the process. For investigation of the flow configuration numerical modeling and simulation has been used.For analysis of the transient jet flow in enclosed areas full 3D geometries with transient simulations yare employed for studying the oscillating jet behaviour in time and space. Aim of the study is the comparison of different chamber geometry variants with non-circular cross sections. Namely, some typical chambers with square and rectangular cross sections with and without streamwise expansion are compared. Two different types of movements are found in the rectangular cavity, namely precession and flapping movement of the jet. The calculations show that further expansion of the main chamber leads to decrement of the flapping and precession frequency in general, as well as an increase of the aspect ratio of D/H leads to a decrease of the flapping movement.