Application of the proper orthogonal decomposition to datasets of internal combustion engine flows

The proper orthogonal decomposition (POD) is applied to both computational fluid dynamics and particle imaging velocimetry data of simplified motored engine flows using two different methods. The first method is to apply the POD to ensembles of velocity fields obtained by considering the flow field taken at fixed crank-angle positions over a number of cycles. As a result, sets of POD modes are found, each of which describe the structure of the flow at a given piston position. These sets give some indication of the instability mechanism involved in tumble breakdown. The second method we use represents a novel approach of applying the POD to flows within a time-varying domain. The velocity fields are stretched to a fixed domain and normalized so that all phases of the flow are equally weighted. In this way, 'phase-invariant POD modes' are created. The phase-invariant modes show desirable properties for forming a suitable basis for future low-dimensional models which should describe the breakdown process more fully.