Three-dimensional (3D) confined wall jets have various engineering applications related to efficient energy dissipation. This paper presents experimental measurements of mean flow development for a 3D rectangular wall jet confined by a vertical baffle with a fixed distance (400 mm) from its surface to the nozzle. Experiments were performed at three different Reynolds numbers of 8333, 10,000 and 11,666 based on jet exit velocity and square root of jet exit area (named as B), with water depth of 100 mm. Detailed measurements of current jet were taken using a particle image velocimetry technique. The results indicate that the confined jet seems to behave like an undisturbed jet until 16B downstream. Beyond this position, however, the mean flow development starts to be gradually affected by the baffle confinement. The baffle increases the decay and spreading of the mean flow from 16B to 23B. The decay rate of 1.11 as well as vertical and lateral growth rates of 0.04 and 0.19, respectively, were obtained for the present study, and also fell well within the range of values which correspond to the results in the radial decay region for the unconfined case. In addition, the measurements of the velocity profiles, spreading rates and velocity decay were also found to be independent of Reynolds number. Therefore, the flow field in this region appears to have fully developed at least 4B earlier than the unconfined case. Further downstream (after 23B), the confinement becomes more pronounced. The vertical spreading of current jet shows a distinct increase, while the lateral growth was found to be decreased significantly. It can be also observed that the maximum mean velocity decreases sharply close to the baffle.

The impinging jet is a complex heat and mass transfer technique that involves several process variables, such as the jet Reynolds number, impingement distance, and jet configuration. In this study, the flow characteristics of a semi-confined circular-pipe impinging jet over different Reynolds numbers and impingement distances were experimentally investigated using a two-dimensional particle image velocimetry technique. The confinement was achieved by positioning a plate parallel to the impinging plate at the nozzle exit. The time-averaged velocity field exhibited a recirculation structure that gradually shifted downstream with increasing Reynolds numbers or impingement distances. Notably, at H/d = 2, this downstream shift of the structure was accompanied by an increase in the vortex intensity. Moreover, the confined plate induced alterations in the overall flow pattern within the confined region, significantly reducing the wall jet decay rate compared with both unconfined and confined radial wall jets for H/d ≥ 3. Conversely, the confinement did not affect the expansion of the wall jet. Unlike the free (unconfined) impinging jets, the semi-confined circular-pipe impinging jet did not exhibit self-similar behavior in the conventional outer-scaled coordinates, particularly concerning the turbulence intensity and Reynolds shear stress. Finally, self-similarity in the time-averaged velocity and various turbulence parameters was achieved using the parameter scale proposed in this study, thereby obtaining the corresponding scaling laws in the wall jet region. Our study results can deepen the current understanding of the flow characteristics of semi-confined circular-pipe impinging jets and are significant for optimizing the performance and efficiency of compact electronic packaging equipment.

This study employs large-eddy simulation to investigate turbulent structures of a planar offset jet characterized by an offset ratio of 5 and a Reynolds number of 7500. A combined diagnostic methodology based on proper orthogonal decomposition (POD), quadrant analysis, and vortex-core-based conditional averaging is used to examine the spatial properties of ejection and sweep events, their contributions to Reynolds shear stress, and their relationship with vortex structures in the present case. POD results reveal that, across most shear layers, the energy-containing and large-scale structures predominantly exhibit extensive ejection or sweep events. Quadrant analysis shows a clear mismatch between the occurrence frequency of ejection and sweep events and their contributions to Reynolds shear stress in the outer shear layers of the pre-attachment and wall jet regions: the more frequently occurring event type does not necessarily make the larger contribution to Reynolds shear stress. However, this mismatch becomes weaker in the inner shear layer of the pre-attachment region, under the influence of the recirculation region, and is largely suppressed in the inner shear layer of the wall jet region, due to the strong near-wall confinement. The vortex-core-based conditional statistics further indicate that the observed frequency-contribution mismatch stems from an imbalance in intensity between vortex-induced ejection and sweep events. The present study, through a combined diagnostic methodology, further deepens the understanding of turbulent structures and the generation mechanisms of Reynolds shear stress within offset-jet shear layers, providing a theoretical reference for understanding pollutant transport, diffusion, and desalination processes under such flow conditions.

To examine the flow characteristics of a three-dimensional wall jet strongly confined by a vertical baffle, flow field measurements were performed on the horizontal and vertical planes crossing the nozzle center using a two-dimensional particle image velocimetry system. The experiment considered four Reynolds numbers: 5084, 8179, 11 052, and 13 926, with a fixed nozzle-to-baffle spacing of 2 d (where d is the nozzle diameter). The results show that the upward and corner wall jets are formed after the three-dimensional wall jet impinges on the vertical baffle. Due to the influence of the recirculation structure on the upward wall jet, it decays more rapidly in the maximum velocity than the corner wall jet. At the same Reynolds number, the jet spreading rates of both jets are comparable. Self-similarity is observed in the normalized time-averaged velocity and Reynolds stress profiles using their half-widths and local maxima values, and their scaling laws are obtained. Two-point spatial correlation and proper orthogonal decomposition analyses reveal that the turbulent structures in the corner wall jet possess lower energy and smaller scales compared to those in the upward wall jet. This study is the first to reveal detailed flow characteristics of the three-dimensional wall jet extremely constrained by a vertical baffle. The findings offer valuable insights for informing the design of engineering structures with complex flow configurations.