An experimental study of inclined negatively buoyant jets released from a sharp-edged orifice was carried out to better understand the re-entrainment phenomenon, i.e. the mixing of jet fluid with itself instead with external fluid, and how it biases the jet behaviour. Experiments reproducing an orifice in the lateral wall of an outfall pipe on the sea bottom were conducted using light-induced fluorescence. The mean and variance of the concentration field have been determined to study the hydrodynamic features along the jet axis, including turbulent mixing and entrainment as the densimetric Froude number varies. The re-entrainment phenomenon tends to appear as the angle exceeds 75° with respect to the horizontal, and its onset occurs for lower angles as the Froude number increases. The re-entrainment biases the behaviour of the jet trajectory, making it bend on itself, and causing a reduction of both the maximum height and distance at the location where entrainment of external fluid reaches the jet axis.

We have developed and validated a new adaptive method, particle tracking velocimetry and accelerometry (PTVA), to measure velocity and acceleration from the post-processing of particle tracking (PT) data. This method is shown to be more accurate than non-adaptive methods based on PT: errors are about six times smaller on velocity measurements and about four times smaller on acceleration ones. We apply this method to a turbulent-like flow generated and controlled in the laboratory. Taking advantage of the Eulerian repeatability of our multi-scale laminar flow, we are able to extract the acceleration field, a, and all terms of Navier–Stokes equation. To complete this we extract u·a and ∇·a fields. We finally compare the probability density function of the acceleration components of our turbulent-like flow with one of the highly turbulent flows and show that they are similar. The quality of these PTVA results and their robustness (in particular to local convection) are extremely encouraging. This method allows access to a deeper insight into the physic of turbulent-like flows and its high accuracy may apply to a broader range of flows.

Turbulence is still an unsolved issue with enormous implications in several fields, from the turbulent wakes on moving objects to the accumulation of heat in the built environment or the optimization of the performances of heat exchangers or mixers. This review deals with the techniques and trends in turbulent flow simulations, which can be achieved through both laboratory and numerical modeling. As a matter of fact, even if the term “experiment” is commonly employed for laboratory techniques and the term “simulation” for numerical techniques, both the laboratory and numerical techniques try to simulate the real-world turbulent flows performing experiments under controlled conditions. The main target of this paper is to provide an overview of laboratory and numerical techniques to investigate turbulent flows, useful for the research and technical community also involved in the energy field (often non-specialist of turbulent flow investigations), highlighting the advantages and disadvantages of the main techniques, as well as their main fields of application, and also to highlight the trends of the above mentioned methodologies via bibliometric analysis. In this way, the reader can select the proper technique for the specific case of interest and use the quoted bibliography as a more detailed guide. As a consequence of this target, a limitation of this review is that the deepening of the single techniques is not provided. Moreover, even though the experimental and numerical techniques presented in this review are virtually applicable to any type of turbulent flow, given their variety in the very broad field of energy research, the examples presented and discussed in this work will be limited to single-phase subsonic flows of Newtonian fluids. The main result from the bibliometric analysis shows that, as of 2021, a 3:1 ratio of numerical simulations over laboratory experiments emerges from the analysis, which clearly shows a projected dominant trend of the former technique in the field of turbulence. Nonetheless, the main result from the discussion of advantages and disadvantages of both the techniques confirms that each of them has peculiar strengths and weaknesses and that both approaches are still indispensable, with different but complementary purposes.

This paper presents conceptual experiments and simulations aiming at controlling flow geometries. Such flow design is performed by driving electromagnetically a shallow layer of brine, the forcing being generated by a transverse electrical current and different combinations of permanent magnets placed underneath the brine supporting wall. It is shown how different basic flow characteristics can be obtained with a single pair of magnets, by varying the angle with the electrical current. These basic flows are proposed as potential building blocks for advanced and complex flows studies. Three typical flow structures are presented to illustrate these building blocks. The discussion is then extended to multi-scale geometry by using blocks of various sizes. The flow is analysed using complementary experiments and numerical simulations. A good agreement is found between the 3D simulations and the experiments for both velocity and acceleration fields, which allows a higher degree of confidence in designing and modelling such flows. As the control of the flow geometry is important for mixing, in particular at low Reynolds number, we also illustrate the different stirring properties of the electromagnetically forced flows by comparing visualisations of passive scalars. They reveal complementary mixing properties for each of the building blocks