Studies in Free Jets from Supersonic ESTS Lobed Nozzles

The flow field associated with supersonic free jets can be understood better by using visualization techniques like schlieren in the laboratory. Supersonic jets are used in the fields of aerospace, refrigeration, and precision manufacturing. The supersonic free jets are normally characterized by a compressible flow field with complex shock structures at off-design conditions. Supersonic free jets from nozzles with exotic shapes like Elliptic Sharp Tipped Shallow (ESTS) lobed nozzle have three-dimensional flow fields that are difficult to completely understand using line-of-sight integrated techniques like schlieren. These nozzles present a challenge to the measurement of flow properties with novel flow diagnostic techniques. Density is one such flow property which is very informative yet difficult to obtain. The three-dimensional density fields can be obtained by the background-oriented schlieren (BOS) [1, 2]. Various nozzle configurations with non-axis symmetric profiles have been studied earlier [3] including the ESTS lobed nozzle [4, 5]. This is an attempt to capture the density flow field of an ESTS lobed nozzle free jet using BOS. In this study, a supersonic ESTS lobed nozzle with four lobes is operated to get a supersonic free jet. The density field of this jet is obtained at several azimuthal positions by turning the nozzle about its axis. The information from all the positions is used to reconstruct the three-dimensional flow field of the nozzle. From this density field, both the basic physics of the complex flow field can be understood as well as CFD modeling of the flow field can be validated.