## 1 Introduction  
Over past several years, rapid advancement has been observed in light-emitting diode (LED) technology. LEDs are now being widely used in residential, commercial, and industrial applications. However, for LEDs, high light output is characterized by more heat. Therefore, thermal management is necessary. Downlights with LED power more than 24 W and light output more than 2000 lumens are now being successfully developed in the market. However, heat sinks with thermal management that relies on nature convection are often heavier and bulkier. In many applications, the device requires extremely high light output but the allowable installation space for the LED lamp is limited. This motivates a compact heat sink with enhanced thermal removal performance. The objectives of this study are to solve the aforementioned problems through the following procedures: (1) to perform simulation and experimental validation to predict the fluid flow and heat dissipation performance characteristics of the designed heat sinks. A traditional heat sink was used as a benchmark to compare various geometries of selective laser melting (SLM)-fabricated heat sinks for compact LED recessed lighting. (2) To study the effects of changing flow velocity for evaluating heat sink performances under turbulent flow conditions. (3) To investigate the SLM-fabricated heat sinks that provide relatively higher Nusselt numbers and lower thermal resistance than traditional heat sinks under jet impingement cooling. Traditionally, air jet impingement cooling is recognized for its high heat transfer rates (i.e., when the temperatures of the impinging jet flow are different from that of the impingement surface). The Reynolds number increases with increasing inlet velocity of air jet impingement. Based on a literature review and our empirical analysis, a higher Reynolds number flow indicates a higher heat transfer rate than that at lower Reynolds number. Therefore, increasing inlet velocity is a vital approach to remove heat from the thermal device. Air jet impingement cooling in a confined space is generated using a cooling fan, which functions as a rotating machinery device. To accurately simulate heat dissipation performance of heat sinks under jet impingement cooling in a turbulent flow field, we used the COMSOL Multiphysics rotating machinery, nonisothermal flow interface with a standard \(k\)-\(\varepsilon\) turbulence flow model, and the frozen rotor study type (COMSOL Inc., Burlington, MA, USA 2017) [1]. Several studies have investigated the \(k\)-\(\varepsilon\) turbulence model and heat transfer characteristics of air jet impingement on heat sinks. The standard \(k\)-\(\varepsilon\) model with realizability constraints is widely used in industrial modeling tools and applications and provides robust and reasonably accurate prediction. The model performs satisfactorily in solving the external flow problems of complex geometries. [PERSON] et al. (2007) [2] investigated the heat transfer of plate-fin heat sinks under impinging jet cooling. The standard \(k\)-\(\varepsilon\) turbulent model was used to perform the simulation. Their simulation results were validated using experimental data. The results indicated that heat removal increases with increasing Reynolds number. [PERSON] et al. (2013) [3] performed a numerical investigation for the turbulent fluid flow and heat transfer characteristics of air jet impingement onto the rotating and stationary heat sink by using four different turbulent models based on Reynolds-averaged Navier-Stokes (RANS) equations. The results of the study indicated that the standard \(k\)-\(\varepsilon\) model provides better predictions for fluid flow and heat transfer performance. Therefore, in this study, we performed numerical simulations for evaluating the heat dissipation performance of heat sinks for CLRDLs using standard \(k\)-\(\varepsilon\) turbulence models based on the Reynolds-averaged Navier-Stokes equations.