The INNpinJeR: A new wall-free reactor for studying gas-phase reactions

Here we characterize the new Innsbruck wall free impinging jets reactor (INNpinJeR) and compare its performance with the TROPOS free jet flow system by quantifying oxidation products of the well-understood...

Analysis of the Vortex Dynamics and Instability Mechanisms for a Lobed Nozzle Jet

The application of radially lobed nozzles has seen renewed challenges in the recent past with their roles in combustion chambers and passive flow control. The free jet flow from such nozzles has been studied for different flow conditions and compared to jets from round nozzles, verifying their improved mixing abilities. The precise mixing mechanisms of these nozzles are, however, not entirely understood and yet to be analyzed for typical jet parameters and excitation modes. While past studies have proposed the presence of spanwise Kelvin-Helmholtz instability modes, the roll-up frequencies of the structures indicate more than one primary structure, which is challenging to resolve experimentally. The present study carries out three dimensional CFD simulations of the flow from a tubular lobed nozzle to identify instability mechanisms and vortex dynamics that lead to enhanced mixing. We initially validate the model against existing hotwire and LDV data following which a range of Large Eddy Simulations (LES) are carried out. The free jet flow was at a Reynolds number of around 5 × 104, based on the effective jet diameter. Initial results are compared to that of a round nozzle to demonstrate changes in mixing mechanisms. The lobed nozzle simulations confirmed the presence of K-H-like modes and their evolution. We also track the formation and the transport of coherent structures from the tubular part of the nozzle to the core flow, to reveal the evolution of the large-scale streamwise modes at the crests and corresponding horseshoe-like structures at the troughs.

Slipping free jet flow near channel exit at moderate Reynolds number for large slip length

The flow of a slipping fluid jet is examined theoretically as it emerges from a channel at moderate Reynolds number. The ratio of the slip length to the channel width $S$ is assumed to be of order one, one order of magnitude larger than the perturbation parameter ${\it\varepsilon}=Re^{-1/2}$, $Re$ being the Reynolds number. Poiseuille flow conditions are assumed to prevail far upstream from the exit. The problem is solved using the method of matched asymptotic expansions. A similarity solution is obtained in the inner layer of the free surface, with the outer layer extending to the jet centreline. The inner-layer thickness grows like $\sqrt{x/Re\,S}$. A slipping jet is found to contract like $x/Re$ very near and far from the channel exit, but does not have a definite behaviour in between compared to $(x/Re)^{1/3}$ for an adhering jet, $x$ being the distance from the channel exit. Eventually, the jet reaches uniform conditions far downstream. As in the case of entry flow, there is a rapid departure in flow behaviour for a slipping jet from the $S=0$ limit. This rapid change is notably observed in the drop of boundary-layer thickness, increase in exit and relaxation lengths as well as in jet width with slip length. Finally, the connections with microchannel and hydrophobic flows are highlighted.

Flow Field Simulation of the Nozzle and the Influence of Size

The nozzle is one of the critical parts in the dry-ice blasting system, spray nozzle's structure and the air supersonic free jet flow field take big influence on cleaning efficiency during the blasting process. Inner flow field of different size nozzles and the flow field of jet flow sprayed by nozzles were simulated with software Fluent, which obtained the distribution results of pressure and velocity of fluid. The result indicated that the supersonic underexpanded jet take place in the nozzle outlet and the shock wave is gained as the pressure at the nozzle exit is greater than the atmospheric pressure. With increasing of the nozzle size, the velocity decrease of airflow become slower, the shock wave transmission distance increase and deduce the stability of the jet flow.