No abstract

In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the supersonic crossflow to minimize the length of the scramjet. Tandem dual-jet injection has shown improved mixing performance over single-jet injection. However, experiments on tandem dual-jet injection have not addressed the jet shear layer, in which the mixing occurs, yet. The present study investigates the jet shear layer, as well as the bow shocks in front of the jets, in a continuous air-indraft supersonic wind tunnel at Mach number 1.55. A schlieren setup has been used for visualizing the flow features. A largely automated algorithm for processing schlieren images has been developed to determine the location of the upper boundary of the jet shear layer. The penetration of the jet is studied as a function of 1) J, the ratio of the momentum of the jet and that of the crossflow, and 2) the dimensionless distance S between the dual-jets. An empirical similarity relation has been established for the time-averaged location of the jet upper shear layer as function of J and S, covering the investigated conditions (J ∈ 2.8;3.8;4.8, S ∈ 0∶9.87). This empirical similarity relation provides S opt , the spacing for maximal penetration of the jets as function of J.

Power minimisation of fluid transport in branched fluidic networks has become of paramount importance for microfluidics, additive manufacturing and hierarchical functional materials. For fully developed laminar flow of Newtonian fluids, Murray's theory provides a solution for the channel and network dimensions that minimise power consumption. However, design and optimisation of networks that transport complex fluids is still challenging. Here, we generalise Murray's theory towards fluid rheologies, including non-Newtonian (power-law) and yield-stress fluids (Bingham, Herschel–Bulkley, Casson). A straightforward graphical approach is presented that provides the optimal radii in a branching network, and the angles between these branches. The wall shear stress is found to be uniform over the entire network, and the velocity profile is self-similar. Furthermore, the effect of non-optimal channel radii on the power consumption of the network is investigated. Finally, examples illustrate how this approach applies to a wide variety of systems.