This study was performed to analyze the effect on driving performance by identifying the flow characteristics of the rear diffuser such as drag coefficient, lift coefficient, velocity vector, velocity streamlines, turbulence kinetic energy and vortex-core region according to the angle of the sedan rear diffuser and the shape of the divider. The angle of the diffuser was analyzed at 2° intervals from 0° to 18°, and the divider was analyzed by changing from one to five. The three-dimensional modeling was performed using CATIA V5 and the vehicle model was selected as a sedan car in the form of an LF Sonata. The CFD analysis was performed in order to identify the flow characteristics of rear diffuser using ANSYS CFX 14.5.7. For each model, the analysis was performed under each condition with speeds of 80km/h, 100km/h, 120km/h, 140km/h. The results of the flow analysis showed that the rear diffuser angle was the best result in driving stability at 6°. The results of the study on the number of dividers showed the best result value in driving stability when the rear diffuser angle was 6° and the divider was 3 and selected as the optimal shape.

The diffuser is effective in closed systems, however, its effect is weaken in open or free flow situations. This can be solved by modifying the rear-end of the diffuser in a manner that enables the formation of strong vortex. By doing that, a large portion of fluid's energy is converted to vortex's dynamic energy, which results in the deduction of static component, or in other words, the decrease of pressure. This study involved the design of rear-end part for efficient hydrodynamic performance of shroud diffusers, and demonstrated with numerical simulation by computational fluid dynamics (CFD). This study focuses on the use of brim end for the shroud where the effect of brim's length and attaching angle are analyzed.

In this study, the flow characteristics at the front and the rear side of the diffuser installed in the AHU for Offshore HVAC system were studied. Set up the rectangular prism of which height is H at diffuser inlet duct, the flow control methods were considered using PIV and CFD numerical analysis. Average flow velocity was increased by 37% and the degree of flow uniformity was 96.7% at x/H =1.5.

In this study, we have modeled a wide angle diffuser with rectangular prism and tried to investigate the influence of a turbulent wake flow by PIV and a numerical simulation using computational fluid dynamics based on steady-state Navier-Stokes equation and standard k-ε model. A commercial CFD program, FLUENT, is used on the analysis. The turbulent wake is generated by a rectangular prism, which is installed at the diffuser. The results show that it is possible to flow control by installing a rectangular prism within the diffuser and velocity recovery is the highest in aspect ratio 1:1.

Recently, products that a have 3-dimensional(3D) micro structure have been in wide use. To fabricate these 3D micro structures, several methods, such as stereo lithography, reflow process, and diffuser lithography, have been used. However, these methods are either very complicated, have limitations in terms of patterns dimensions or need expensive components. To overcome these limitations, we fabricated various 3D micro structures in one step using a pair of diffusers that diffract the incident beam of UV light at wide angles. In the experiment, we used positive photoresist to coat the Si substrate. A pair of diffusers(ground glass diffuser, opal glass diffuser) with Gaussian and Lambertian scattering was placed above the photomask in the passage of UV light in the photolithography equipment. The incident rays of UV light diffracted twice at wider angles while passing through the diffusers. After exposure, the photoresist was developed fabricating the desired 3D micro structure. These micro structures were analyzed using FE-SEM and 3D-profiler data. As a result, this dual diffuser lithography(DDL) technique enabled us to fabricate various microstructures with different dimensions by just changing the combination of diffusers, making this technology an efficient alternative to other complex techniques.

For the purpose of improving the durability problem, translucent opal glass was fabricated as a substitute for the polycarbonate diffuser of LED lighting. Calcium phosphate was used as an opacifier of opal glass and melted in an electric furnace. The opaque effect was identified according to the change of the cooling procedure. As results, translucent opal glass was obtained by the melting of a batch with a composition of 3.8% calcium phosphate at 1550˚C for 2 hrs and then the cooling of the material in the furnace. For the cooling condition of the glass sample, HTCG (High Temperature Cooled Glass) was found to have better optical properties than LTAG (Low Temperature Annealed Glass). It had excellent optical properties for a diffuser of LED lighting, with no dazzling from direct light due to its high haze value of over 99% and low parallel transmittance value of under 1%. For the thermal properties, it had an expressed thermal expansion coefficient of 5.7×10-6/˚C and a softening point of 876˚C; it also had good thermal properties such as good thermal shock resistance and was easy to apply to the general manufacturing process in the forming of glass tubes and bulbs. Therefore, it is concluded that this translucent opal glass can be used as a glass diffuser material for LED lighting with high heat resistance and high durability; this material is suitable as a substitute for polycarbonate diffusers.

In this study, a computational work to investigate the influence of a turbulent wake flow by a rectangular prism with different aspect ratio, which is installed at the inlet of a diffuser. The k-ω model was adopted to simulate the turbulence. The continuity and time averaged Navier-stokes equations were solved by a implicit finite volume scheme. The computational results are qualitatively well compared to existing experimental data by PIV. The results show that the velocity recovery of the subsonic diffuser is dependent on the aspect ratio of rectangular prism.

In this study, a experimental work to investigate the influence of a turbulent wake flow on the velocity distribution of a diffuser with PIV method. The turbulent wake is generated by a rectangular prism, which is installed at the inlet of a diffuser. The results show that the velocity recovery of the subsonic diffuser is dependent on the height and location of rectangular prism. It is found that a certain height of the rectangular prism to generate the turbulent wake give a better velocity recovery, compared with no rectangular prism.

In this paper, the relationship between static pressure recovery and turbulent energy was presented in case of swirling flows into a conical diffuser. The distributions of turbulent energy in a diffuser sectional area were measured by a hot wire anemometer. The following conclusion can be drawn from the experiment. Diffuser loss is constituted by a dynamic pressure loss and total pressure loss. The static pressure recovery depends strongly on the total pressure loss. The static pressure recovery depends strongly on the total pressure loss, and the turbulent energy varies inversely as the static pressure recovery coefficient.

The purpose of this paper is to investigate the relationship between static pressure recovery and velocity distributions in case of swirling flow into a conical diffuser. In this research, velocity distribution is measured by a multi-hole yaw-meter. The following conclusions can be drawn from the experiments. (1) The static pressure recovery depends strongly on the strength of a swirl. (2) A high pressure recovery coefficient is achieved by inserting a solid core into the diffuser center.