Iis Rohmawati

<jats:p>The heat loss through the walls of Internal Combustion Engines (ICEs) needs to be minimized and improved since it has a detrimental impact on the overall thermal efficiency of the engine. This study focuses on investigating heat transfer in a flat-wall impinging diesel spray flame, simulating diesel conditions, to optimize engine parameters. The effects of factors such as various injection pressures, nozzle hole diameters, impingement distances, and oxygen concentrations are analysed in combined and individually. Experimental techniques, such as high-speed imaging, heat flux sensors, and thermocouples, are used to visualize spray flame, measure heat flux profiles and temperature distributions, respectively. Preliminary results and their implications on heat transfer and heat loss are discussed. Regarding the parametric studies investigating the effect on wall heat loss under conditions similar to those of a small diesel engine, it was observed that the transferred heat on the wall was significant in certain conditions. These results emphasize the effectiveness of manipulating the injection rate profile as a viable step to suppress the heat transfer through the wall.</jats:p>

<jats:p>A rectangular wing with Wavy Leading Edge (WLE) effect was investigated experimentally and numerically. This research was carried out with the NACA 0018 profile. The morphology of humpback whale flippers, which are blunt and rounded in a specific pattern, inspired the design of the WLE. The rectangular wing was explored in pitching motion with a reduced frequency of k = 0.25 and varied aspect ratios. Multiple aspect ratios (AR) of the rectangular wing have been evaluated to determine the best wing aspect ratio, notably 3.9, 5.1, and 7.9. Only at AR 3.9 and 5.1 does the WLE perform efficiently in both upstroke and downstroke motion. WLE has a sinusoidal function shape. The improvement of lift force was stronger during upstroke motion than during downstroke motion. The stall is minimized during the pitching motion of the WLE wing, according to the numerical simulation. This result could be applied to fin stabilizers or wind turbines.</jats:p>

<jats:p>Increasing heat transfer and heat transfer coefficient as the combined effect of impingement distance and injection pressure has been explored in the previous report. However, local temperature distribution was limited to the discussion. Clearly, investigation of near-wall temperature in the heat transfer analysis is absolutely necessary. This has a crucial effect on the local heat flux to understand the heat transfer phenomenon on the combustion chamber walls. The local temperature and KL factor were investigated by using a high-speed video camera and a two-color method by using a volume vessel with a fix-impingement wall. We found that the local temperature and KL factor distribution increase in low injection pressure. This result had a dominant effect on local heat transfer.</jats:p>

<jats:p>Experimental and numerical research have been performed to investigate the Wavy Leading Edge (WLE) effect on the rectangular wing. The WLE is inspired by humpback whale flipper morphology which is blunt and rounded in certain form pattern. This flipper shape plays an important role for its behaviour specially capturing their prey. This advantage could be applied to other systems such as fin stabilizers or wind turbines. Steady cases in various aspect ratios were conducted to find out the optimum effect of WLE with baseline NACA 0018 profile at Reynolds number 1.4 x 105. The chord length of the wing (c) was 125 mm. The WLE shape defined as wavelength (W) 8% of c and amplitude (d) is 5% of c. The aspect ratio (AR) variations were 1.6; 3.9; 5.1; 7.9 and 9.6.  A simple rectangular form of the wing was selected to analysis the WLE effect on the various ARs. The taper wing shape is applied to find out the WLE effect at the AR 7.9. three types of taper ratio (TR) are 0.1; 0.3 and 0.5. The results show that the WLE on the taper wing has better advantage to control the stall in steady case. Another impressive result was the WLE wing with AR 7.9 and TR 0.3 has the best lift coefficient and pressure distribution.Keywords: stall, wavy leading edge, steady case, rectangle wing, taper wing, aspect ratio. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Learning from nature, the humpback whale can swim faster than other baleen whales. The humpback whale has the flipper with wavy leading edges (WLE), which has an improvement of hydrodynamic performance. The WLEs have the function to generate vortices to maintain lift and to prevent stall at high angles of attack. This research aim is to find out the WLE effect on hydrodynamic performance in different wing aspect ratios (AR), whose profile is the rectangular wing of NACA 0018 as a baseline wing. The WLE profile was designed by a sinusoidal function. We focused on steady flow conditions in both the experiments and numerical simulations. The experimental work was conducted in the circular water channel at Hiroshima University, Japan. Meanwhile, the numerical work was employed using RANS simulation with SST k-ω turbulence model. Based on the results, we clarified that the increase of AR could possess a higher lift coefficient (Cl), and then physically interpreted the WLE effect on various aspect ratios. This knowledge could be expanded into the application of eco-friendly energy-saving devices such as fin stabilizers of ships and wind turbines to improve hydrodynamic performance.</jats:p>