A solar air heater (SAH) is a simple heater using solar radiation that is useful for drying or space heating. Unfortunately, heat transfer from the absorber plate to the air inside the solar air heater is low. Some researchers reported that obstacles are able to improve the heat transfer in a flat plate solar air collector and others found that a v-corrugated absorber plate gives better heat transfer than a flat plate. Yet, no work of combining these two findings is found.This paper describes the result of experimental study on a SAH with v-corrugated absorber plate and obstacles bent vertically started from 80oto 0owith interval 10oon its bottom plate. Experiments were conducted indoor at five different Reynolds numbers (1447 Re 7237) and three different radiation intensities (430, 573, and 716 W/m2).It is found that the obstacles improve SAH performance. Both the air temperature rise and efficiency increase with inserting obstacles bent at any angle vertically. Unfortunately, the air pressure drop is increasing, too. Obstacles bent vertically at smaller angle (means more straight) give higher air temperature rise and efficiency. However, the optimum angle is found 30o. The air temperature rise and efficiency will be 5.3% lower when the obstacles bent 30oinstead of 0o, but the pressure drop will be 17.2% lower.
Turbulent boundary layer plays an important role for generation of aerodynamic drag. Shear force and pressure force due to the presence of boundary layer separation from the body surface contribute to the total drag. Studies of drag reduction due the the boundary layer effect are continuously performed by many researchers. Present study is intended to evaluate the behaviour of the laminar sub-layer in a turbulent boundary layer using a hot-wire anemometer system. The study was conducted in a low-speed wind tunnel at a Reynolds number based on the momentum thickness of approximately Reθ = 1000. A smooth-flat plate and a plate with a single transverse square groove was used in the study of the boundary layer characteristics. The groove size of 10 mm x 10 mm was cut transversally across the test plate. The results show that no significant differences in the streamwise mean velocity, steamwise turbulence intensity, and velocity signals for the smooth-and grooved-wall cases. For the the energy spectra for the two cases, however, show significant differences.
Boundary layer flow structure developing on an airfoil surfaces strongly affects drag and lift forces acting on the body. Many studies have been done to reduce drag, such as introducing surface roughness on the airfoil surface, gas injection, attachment of vortex generators, or moving surface on the airfoil. Previous results showed that the attachment of vortex generators has potentially been able to control boundary layer separation compared to other controlling devices. This study is focused on the evaluation of the effect of vortex generator attachment on the NASA LS-0417 airfoil profile as this profile is commonly used in wind turbine blade application. The models of this experimental study are NASA LS-0417 profiles, with and without vortex generator. The chord length of the profile is 110 mm, while the span is 210 mm. Profile of the vortex generator is a symmetrical profile of NACA 0012 configured in counter rotating and attached on the upper surface of the main profile. The chord length of the vortex generator is 7 mm with two different values of the height (h): 1 mm and 2 mm. The experiment was conducted in an open loop wind tunnel with maximum attainable freestream velocity of approximately 19 m/s and the turbulence intensity at the tunnel centerline is approximately 0.8%. The wind tunnel cross section is octagonal of 30 cm x 30 cm and of 45 cm to 60 cm adjustable length. The study was performed at two different freestream velocities of 12 m/s and 17 m/s corresponding with Reynolds numbers (Re) of 0.83 x 105 and 1.18 x 105 based on the airfoil chord length and the freestream velocity. Angle of attact (α) was varied from 0o to 24o. Drag and lift were measured using a force balance with measurement uncertainty of approximately 0.77% and 2.47% at measured drag of 0.65N and at measured lift of 0.202N, respectively. A flow visualization study using oil flow method was conducted to obtain qualitaive picture of flow structure on the airfoil surface. Results of this study showed that attachment of the vortex generator on the NASA LS-0417 profile has not been able to improve the profile performance compared to that of unmodified profile. There, however, seems Reynolds number effect on the airfoil performance flow conditions performed in this study. At lager Re, there is an increase in CL/CD of approximately 36% at angle of attack (α) 6o. Next, based on the flow visualization results, attachment of the 2mm vortex generator on the airfoil NASA LS-0417 surface results in an advancement of boundary layer separation at the two Re’s conducted in this study. Finally, the 2mm vortex generator accelerates airfoil stall at approximately 16o, while the 1mm vortex generator is relatively no effect on the airfoil stall angle.
Wings are a very important part of aircraft. In that section, most of the lift forces are generated on the airplanes. The aerodynamic performance produced by the wing greatly determines how optimal the cruising range of an aircraft. To improve the performance of the wings, researchers have been competing to make wing modifications of an aircraft. One modification that is used at this time is by adding end wall which is often referred to as a winglet. Winglets function as a barrier to fluid flow jumps from the lower surface to the upper surface. This fluid flow jumps is often called as a tip vortex. One type of winglet discussed in this study is the wingtip fence. This study took wing objects on unmanned aerial vehicle with numerical simulation using Ansys 19.0 software with turbulent model k-ω SST. The freestream flow rate to be used are 10 m/s (Re = 2,34 x 104) and 45 m/s (Re = 1 x 105). The angle of attack used are (α) = 0°, 2°, 4°, 6°, 8°, 10°,12°,15°, 17°, and 19°. The wing model is an Eppler 562 (E562) airfoil with and without a winglet. From this study, it was found that wing aerodynamic performance with Eppler 562 (E562) airfoil was higher at Re = 2,34 x 104 Delay of the stall is more effective at Re = 1 x 105 compared to the Re = 2,34 x 104 But, the aerodynamic performance Re = 2,34 x 104 better than Re = 1 x 105.
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