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 หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Visualization of Thermal Structure of Turbulent Spot under Adverse Pressure Gradients Using Liquid Crystals) ผู้เขียน: Weerachai Chaiworapuek, Suttaya Nongnoi,  ดร.ชวลิต กิตติชัยการ, รองศาสตราจารย์ สื่อสิ่งพิมพ์:pdf AbstractThe pressure gradient affects the stretching and retracting of a streamwise length of the transition zone of a fluid flow over a flat plate. Furthermore, the turbulent spot is directly controlled in size by the pressure gradient. The details were investigated of the evolution of the thermal footprint (the area of heat transfer underneath a turbulent spot) using thermochromic liquid crystals under various adverse pressure gradients. The experiment was carried out over an isothermal flat plate in a low turbulence water tunnel with a turbulent intensity of 0.925%. Information was obtained on the development of the temperature, the heat transfer coefficient and the heat flux contours of the footprint as it propagated downstream. All spot parameters in this study, achieved from the use of the developed image processing code were slightly different to those reported by others. The heat transfer characteristics of the footprint were deduced by an “implicit” heat balance approach. Moreover, the characteristics of the turbulence breaking down under the influence of adverse pressure gradients were presented by representative structures of the turbulent spot footprint. Thus, these results could be applied as qualitative and quantitative data into numerically predictive formulas, used for the flow under a boundary layer transition, induced by an adverse pressure gradient. |
หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Heat Transfer Measurement on a Turbulent Spot Using the Energy Balance Method) ผู้เขียน:Weerachai Chaiworapuek, Suttaya Nongnoi, ดร.ชวลิต กิตติชัยการ, รองศาสตราจารย์ สื่อสิ่งพิมพ์:pdf AbstractA turbulent spot is a small turbulent patch, surrounded by laminar flow at a boundary layer transition. It is an important mechanism, clearly showing the characteristics of highly turbulent flow and heat transfer inside the body. However, measurement in heat transfer from a flat plate to a fluid via a turbulent spot remains difficult due to the unsteady and unstable nature of the site. This paper detailed a temperature measurement technique using a coating of thermochromic liquid crystal. An analytical solution, derived from the developed energy balance method and an image processing technique were combined to visualize the thermal footprint of a turbulent spot. The experiment was performed over an isothermal flat plate in a low turbulence water tunnel where the turbulent intensity was lower than 1%. Reynolds number was initially kept at 75,000, as a reference rate for laminar flow. Transitional flow was bypassed by a small disturbance injection. The results were presented qualitatively and quantitatively using color, temperature, the heat transfer coefficient and heat flux as spots were propagated downstream. The locations of the leading and trailing edges were also clearly visualized. Turbulent spot information (spot celerities and the half spreading angle) were in agreement with those obtained by the other researchers, confirming the reliability of this technique. Thus, this energy balance method can be applied effectively to obtain insight into the bypass boundary layer transition over a flat plate. |
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 Researcherดร. วีรชัย ชัยวรพฤกษ์, รองศาสตราจารย์ที่ทำงาน:ภาควิชาวิศวกรรมเครื่องกล คณะวิศวกรรมศาสตร์ สาขาที่สนใจ:Flow Visualization Techniques, Boundary Layer Transition, Application of Liquid Crystals in Fluid and Thermal Engineering, Heat Transfer on the heated Surface Resume |
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