# Advances in Riblets Design
###### Abstract
Moreover, riblets show promise for adaptation to various flow control applications for drag reduction, such as aviation, marine ships, automotive, wind energy, sports, and medical fields [1; 2; 3; 17; 31; 32; 33]. Since the first fundamental studies on riblets by the NASA Langley Research Centre in the 1970s [34], many studies have been conducted that show immense potential for drag reduction and greenhouse reduction by sharkskin-inspired riblets in aviation [18; 29; 35; 36; 37; 38; 39; 40]. [PERSON] estimated that riblets could lead to a 2% draft reduction by an Airbus 320 if 70% of the aircraft is covered with riblets. In 1987, the racing yacht \"Stars and Stripes\" with the implementation of riblets from NASA and 3M won the America's Cup and the gold medal at Olympia [41]. In 2010, the BMW Oracle team won the 33 rd America's Cup with their racing yacht covered with riblets [42], In 2012, riblets found their applications on wind turbine blades [31] and a Formula 1 car by Bionic Surface technology [43]. Moreover, riblets' antifouling properties have been studied for potential applications on marine ships, medical implants, water treatment systems, and food and beverage industries [44; 45; 46]. Despite the common underlying physics of riblets in drag reduction and other applications, translating riblet technology to different domains poses challenges related to scale, environmental conditions, and surface materials. As an example, in the field of wind energy, wind turbine blades require considerations of larger scales and dynamic load variations, while underwater vehicles involve hydrodynamic complexities. Ensuring the robustness and durability of riblet structures in diverse conditions, as well as addressing manufacturing and maintenance aspects, are key challenges when applying riblet technology [14]. These surfaces have been widely studied during the past few decades. Experimentally, they have been tested with different methods: evaluated in oil [47], water [7; 48; 49] or wind tunnels [25; 31; 50; 51; 52; 53] or viscosity base counter-rotating cylinders, like the Taylor-Couette cell device [54]. Moreover, they have non-dimensional geometrical characteristics that facilitate the comparison between different studies, both in experimental and numerical research activities. Several authors [25; 55; 56; 57; 58; 59] have conducted their research in a manner that allows for the evaluation of their work alongside other references. In the laboratory environment, riblets have been investigated in open-loop or closed-loop channels. In addition, research activities have been conducted on simple flat plates or standard extrude airfoil sections, with the possibility of testing different crossflows and angles of attack in test plates, allowing variable sweep conditions and different pressure gradients, which form more realistic conditions and mimic real flight. Moreover, several studies related to aircraft-generated noise and solutions for reducing noise at source have been reported in the literature. The source targeting techniques are introduced to control generated noise by manipulation, altering and inhibiting [60] at the locations where sources of noise are forming. One type of self-noise, which is especially dependent on industrial applications, is the noise generated inside the fully developed turbulent boundary layer over the airfoil trailing edge. To investigate and mitigate the effect of airfoil trailing edge noise, experimental activities have been conducted during the past decades. The use of serrations, porous surfaces and pressure shielding are some of the solutions that work by altering the turbulent boundary layer developed over the trailing edge [60]. As an example, [PERSON] et al. [61] made modifications over the trailing edge to control noise at diffusion airfoils by using grooves on both sides with a detached pattern on the endpoints. As near-wall flow structures are altered by riblet geometries, the effect of these geometries on noise reduction was also studied [25; 51].