But, once this function is known all other points with the same flow parameters will have the same heat transfer rate. Thus, heat transfer is a local problem and thus can be predicted when the steady-state flow is known. One has to know also the geometry and the state of the flow at each point of time in the whole flow field. The unsteady pressures generated on an oscillating surface depend on the relative geometry changes during the oscillation cycle, pressure waves propagate in the flow field from one spot to another and vibrating bodies in a flow field or phenomenon like vortics and flow separations modify the time-dependent flow field itsself. Thus, unsteady flow is a global problem because to predict it one needs not only to know the local flow properties but one needs also a lot of information about the world around.
Simplifications are possible.
But, strictly spoken each flow problem is unique as regards to its unsteady behaviour. However, with some simplifications it is possible to predict a lot of flow cases that are important for turbomachinery. A major task of the research in unsteady aerodynamics is to find out what are reasonable simplifications in numerical codes and to provide experimental data to check these codes. Industrial partners Research projects at the LTT are usually conducted in close collaboration and with support from industrial partners.