Because of their effectiveness and adaptability, impinging jets have found their way into a host of applications ranging from cooling turbine blades, to heat management of electronic systems. With constantly increasing demand for efficient and compact cooling systems in certain industries, such as the aerospace or electronics industries, variations on the textbook-setup of an impinging jet have been studied over the years. One such variation introduces a periodic disturbance into the jet that can have an effect on both the structure of flow and the thermal boundary layer at the target surface. In what follows is a short overview of studies having used pulsed jets, often in tandem with other modifications, to try and improve heat transfer. Special attention was also given to the methods by which the periodic disturbance can be produced since they involve setups of different levels of complexity and having different implementation costs.

This study investigates the performance of lattice-structured heat sinks based on BCCz unit cells in comparison to conventional straight-fin and pin-fin designs. Various lattice configurations were explored. Numerical simulations and experimental evaluations were carried out to analyze thermal resistance, pressure drop, and temperature distribution under different operating conditions. Among the designs, the BCCz configuration with a circular cross-section was identified as the most promising candidate for integration into the final heat sink demonstrator, offering reliable and consistent performance. A prototype using the BCCz lattice structure was additively manufactured, alongside a conventional design for comparison. The results highlight the superior heat dissipation capabilities of lattice structures, achieving up to a 100% improvement in thermal performance at high flow rates and up to 300% at low flow rates compared to a conventional straight-fin heat sink. However, the pressure drop generated by the lattice structures remains a challenge that must be addressed. This work underscores the potential of optimized lattice-based heat exchangers to meet the severe thermal management requirements of railway power electronics.

Fluidic oscillators are no-moving-part actuators that can be used to produce pulsating jets. The characteristics of these devices and of the flow fields they produce are of particular interest in the field of heat transfer, as pulsating impinging jets have been shown to improve heat transfer compared to steady jets. In this study, special focus is given to these characteristics as a preparation for a subsequent thermal study that will evaluate the performance of these pulsed jets against steady jets. The functioning of the device in response to different operating and design parameters is first considered. It was shown that a transition between different operating modes is possible, depending on both the inlet mass flowrate and the width of the feedback channel of the device. This was followed by a study of the velocity fields of the pulsed jets produced by the device. More specifically, attention is given to the developing characteristics and flow structures of the pulsating free jets of air which are then compared to equivalent steady jets. Finally, by taking advantage of the periodic aspect of the flow, the phase-averaged velocity field was reconstructed. Vortex dipoles were detected, tracked and their convection velocity computed from the same data and compared to a theoretical value from the literature. A proper orthogonal decomposition (POD) of the synchronized raw data was then performed to further highlight the presence of these vortex structures and other flow instabilities.

Sub-millimetric synthetic, continuous, and pulsed-jet actuators under identical conditions of generation are experimentally compared. Particle image velocimetry and hot-wire anemometry were used for measuring the velocity field. In the second part of the article, the interaction of these three types of actuators with a transverse external flow is characterized using the same experimental techniques. The studied plate is bended downstream from the actuator. Two angles are studied—0° and 28°. The efficiency of the fluidic action on the reattachment of the boundary layer is shown to be strongly dependant on the type of the jet.