Assessment of the efficiency of the use of activating turbulent jets to eliminate the risk of the formation of unventilated zones in large premises

Strict requirements for microclimate parameters are imposed on food storage premises, which are equipped with artificial cooling systems. The experience of operating the refrigerated premises revealed the following disadvantages: uneven distribution and significant fluctuations in temperature and relative humidity; periodic precipitation of condensate in low-temperature sections. Elimination of the noted disadvantages is effectively achieved by using axial fans that form a swirling air stream that induces the ambient air. Swirling jets used to intensify the process of air circulation in a room in order to eliminate unventilated zones will be called activating jets. To assess the efficiency of the application of activating turbulent jets, an integral method based on the energy balance was used. Using the example of a representative object, it is shown that the distance of the effective application of an activating turbulent jet should be calculated taking into account the influence of environmental turbulence, which is determined by the amount of energy introduced and dissipated in the room.

Experimental study of heat transfer of impinging swirling jets and jets with chevrons

The aim of this work is to study the effect of different forms of passive change in the shape of the flow on the intensity of heat transfer in the impact jet. In this work, a cycle of experiments was performed to investigate an axisymmetric jet flowing normally onto a heated surface. The jet was located both in natural conditions and during swirling of the flow (S = 0.4; 0.7; 1.0). It is shown that the intensity of heat transfer on a heated target in the case of a chevrons jet has little effect on the character, but significantly intensifies heat transfer. In the case of a swirling jet, the intensity distribution on the wall changes its character and locally increases at small distances between the nozzle and the heater.

Obtaining Expressions for Time-Dependent Functions That Describe the Unsteady Properties of Swirling Jets of Viscous Fluid

Previously, it has been shown that the dynamic geometric configuration of the flow channel of the left heart and aorta corresponds to the direction of the streamlines of swirling flow, which can be described using the exact solution of the Navier–Stokes and continuity equations for the class of centripetal swirling viscous fluid flows. In this paper, analytical expressions were obtained. They describe the functions C0t and Г0t, included in the solutions, for the velocity components of such a flow. These expressions make it possible to relate the values of these functions to dynamic changes in the geometry of the flow channel in which the swirling flow evolves. The obtained expressions allow the reconstruction of the dynamic velocity field of an unsteady potential swirling flow in a flow channel of arbitrary geometry. The proposed approach can be used as a theoretical method for correct numerical modeling of the blood flow in the heart chambers and large arteries, as well as for developing a mathematical model of blood circulation, considering the swirling structure of the blood flow.

The Role of the Centerbody Wake on the Precessing Vortex Core Dynamics of a Swirl Nozzle

The precessing vortex core (PVC) phenomenon in swirling jets is a helical instability in the flow driven by the coherent precession of the vortex breakdown bubble (VBB) around the flow axis, resulting in the helical rollup of the shear layer. This instability is driven by flow processes in the region upstream of the VBB. Centerbodies, commonly employed in combustor nozzles, create a centerbody wake recirculation zone (CWRZ) that can interfere with VBB precession and hence suppress the PVC. We study this phenomenon in a swirl nozzle with a centerbody whose end face is flush with the nozzle exit plane, using large eddy simulations (LES) and linear hydrodynamic stability analysis for flow Reynolds numbers Re = 48,767 and 82,751, based on nozzle exit diameter and bulk flow velocity. For one of the Re = 82,751 cases, the centerbody end face diameter is halved, resulting in the onset of coherent VBB precession. Linear stability analysis reveals a marginally unstable mode in this case. The same mode is found to be stable in the nominal cases. Structural sensitivity analysis shows that the VBB precession eigenmode is sensitive to changes in the time-averaged flow in the VBB-CWRZ merger region. This suggests that the reduction in CWRZ length due to halving the centerbody end face diameter is the reason for the onset of VBB precession. These results suggest that in general, spatial separation between the CWRZ and VBB can result in the onset of VBB precession and the emergence of PVC oscillations in flows with swirl.

Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.