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...

Experimental study of the heat transfer of two parallel impinging jets

Local and integral characteristics of heat transfer are obtained at varying the Reynolds number Re = 5500, 11000, the distance between the jets y/D = 1.8, and the distance from the jets to the surface z/D = 0.5-10 for the system of two identical impinging jets. It is found in experiments that the effect of an adjacent jet leads to enhancement of local heat transfer at large distances between the nozzles and the barrier. It is also shown that an increase in the Re number increases integral heat transfer, and, at the same time, weakens the inter-jet interaction. The paper analyzes the scenarios of the behavior of local and integral heat transfer depending on the geometric and flow parameters of the system of two circular turbulent jets.

Development of flow control methods in free and impinging jets

Submerged and impinging jets with harmonic perturbations added to the inlet velocity profile and with nozzle vibrations are simulated numerically at different Reynolds (Re) and Strouhal (St) numbers by solving the Navier–Stokes equations. The effects of Re, St and forcing amplitudes on flow behavior and jet splitting phenomena are studied.

Influence of nozzle external geometry on wavepackets in under-expanded supersonic impinging jets

In this study, large-eddy simulations are utilised to unravel the influence of the nozzle's external geometry on upstream-travelling waves in under-expanded supersonic impinging jets. Three configurations, a thin-lipped, a thin-lipped with a sponge and an infinite-lipped nozzle are considered with the other non-dimensionalised geometrical and flow variables identical for the three cases. Spectral proper orthogonal decomposition is applied to the Mack norm, i.e. the energy norm based on the stagnation energy, to obtain the spatial modes at their corresponding frequency. The spectral decomposition of the spatial modes at optimal and suboptimal frequencies is used to isolate the wavepackets into upstream- and downstream-propagating waves based on their phase velocity. It is found that the external geometry of the nozzle has a significant influence on the first-order statistics even though the governing non-dimensional parameters are the same for all three cases. Multiple peaks emerge in the energy spectra at distinct frequencies corresponding to axisymmetric azimuthal modes for each case. The downstream-propagating wavepackets have a high amplitude at the shear layer of the three jets with the mode shapes resembling Kelvin–Helmholtz instability waves, while the upstream-travelling wavepackets exist in the three regions of the near field, shear layer and inside of the jet. The barrel shock at the nozzle exit appears as a flexible shield, which prevents upstream-travelling waves from reaching the internal region of the nozzle, where the upstream-travelling waves travel obliquely with one side of the wavefront is crawling on the reflected shock while the other side is guided by the shear layer. These latter waves can reach the nozzle lip via inside of the jet. The spectral decomposition of the spatial modes at optimal and suboptimal frequencies show that all three forms of the near field, shear layer and inside jet upstream-travelling wavepackets contribute to the receptivity process while their contributions and strength are altered by the change of the external geometry of the nozzle.

Study of the influence of an external flow rate perturbation on the vortex structure and heat transfer in impinging jets

The study of physical processes dominating in submerged turbulent jets impinging on a wall is an important task because this configuration is utilized in various applications. The efficiency of heat transfer in this configuration has been a subject of a long-term study. Active flow control technique and the optimization of the control signal can be applied to exploit inherent flow properties to further improve the heat transfer from the wall in impingent jets. In this paper, IR-thermography and time-resolved PIV measurements are used for the diagnostics of wall temperature fields and large-scale vortex dynamics under external flow rate forcing control. It is found that the low-frequency forcing (for the Strouhal number St = 0.6) increases integral temperature on the wall as compared to the unforced case and the high-frequency forcing (St = 0.9).