Liquid Crystal Visualization in The Study of the Flow in a Shallow Cavity

Using the example of a flow around a shallow cavity, the possibilities of liquid-crystal visualization at subsonic and supersonic flow velocities are demonstrated. To determine the flow structure at the bottom of the cavity, a coating based on a composition of pure cholesteric liquid crystals (ChLC) was used. To determine the distribution of temperatures and heat fluxes, thermosensitive films formed by encapsulation of ChLC in a polymer matrix were used. Based on the experimental results, the influence of the Mach number on the spatial pattern of the flow inside the cavity and the temperature distribution at the bottom of the cavity was obtained. The pattern of surface streamlines obtained by the LC coating coincides with that obtained using the oil film visualization. In this case, the LC method makes it possible to compare the values of shear stresses in different parts of the surface also. It is found that the occurrence of resonance phenomena leads to restructuring of the flow inside the cavity and a change in the values of shear stresses. It is shown, that in subsonic flow around the zone of increased heat transfer is concentrated near the axis of symmetry of the cavity.