What are the different methods of flow visualization?

in this case we need more information about what kind of flows are refered to ... also what kind of subject we are talking about, could be thermodynamics or production process in a company, so we will assume that we ask on the subject of thermodynamics, for this we have 3 kinds of flow visualization, surface flow visualization, particle tracer methods and optical methods this 3 methods are used for flow visualization in fluid dynamics.