Effect of rounded edged dimple arrays on the boundary layer development

Journal of Visualization12117-2

Investigation of indentations versus surface roughness for fluid induced motion of an elastically attached circular cylinder at velocities relevant to the marine environment using CFD

Vortex induced vibration aquatic clean energy (VIVACE) is a renewable energy (RE) device being developed that uses multiple oscillating circular cylinders in one degree of freedom to produce electrical energy due to fluid induced motion (FIM). VIVACE is a modular system intended for use in ubiquitous slow velocity water flows of rivers, tides and ocean currents. Velocities of 1 to 5 knots are to slow for use by turbines and represents a massive opportunity for widespread, continuous RE power. VIVACE currently uses passive turbulence control (PTC), a pair of symmetrical roughened surfaces on the circular cylinder to increase amplitudes and therefore increase power output. PTC works by effecting the fluid-structure interaction (FSI) within the boundary layer and the separation of the water from the cylinder creating changes in the characteristics of forces on the cylinder. The problem with a roughened surface in the marine environment is become fouled by marine organisms and therefore lose its effectiveness. The intent of this research is to investigate the likelihood of biofouling of the PTC and suggest an alternative using indentations partially covering a circular cylinder to act in a similar wat to PTC increasing amplitudes. Indentations are an alternative design because they have smooth surfaces which can be treated with anti-biofouling coatings while still creating the disturbance to the boundary layer mechanism that causes the increased amplitude. A review of FIM, FSI and computational fluid dynamics (CFD) is conducted to inform the research. A literature review is conducted on topics of current FIM technologies, surface roughness and indentation research on FIM and marine biofouling. The literature analysis strongly suggests that biofouling will be an issue for the current VIVACE PTC design. CFD using ANSYS is conducted to baseline the design against existing studies and then investigate four cases of indentations. Of the four indentation designs trialled they produce a reduced amplitude compared to PTC or completely dampened FIM. Further research with improved computational resources is required to complete this work

Novel cooling strategies for improved protection of gas turbine blades

Modern gas turbines are operating at peak turbine inlet temperature well beyond the maximum endurable temperature of turbine blade material. As a result, hot gas-contacting blades or vanes have to be cooled intensively by using various cooling technologies, such as film cooling and internal cooling, in order to increase the fatigue lifetime of the engine. In the present study, a series of experimental investigations were conducted to explore innovative cooling strategies for improved exterior and interior cooling of gas turbine blades. For the exterior cooling, the effectiveness of novel film cooling designs with coolant injection from Barchan-Dune-Shaped ramp (BDSR) and Barchan-Dune-Shaped injection compound (BDSIC) were evaluated in great detail, in comparison to that of conventional circular holes. While a high-resolution Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the dynamic mixing process between the coolant streams and the mainstream flows over the test plates, Pressure Sensitive Paint (PSP) technique was used to map the corresponding adiabatic film cooling effectiveness on the surface of interest based on a mass-flux analog to traditional temperature-based cooling effectiveness measurements. The measured effectiveness maps were correlated with the characteristics of the flow structures revealed from the detailed PIV measurement in order to elucidate underlying physics to explore/optimize design paradigms for a better protection of the critical components of turbine blades. Beside exploration of novel cooling designs for film cooling, an experiment was performed to examine the compressibility effect on film cooling effectiveness by using PSP and PIV technique. The experimental studies were conducted in a transonic, open-circuit wind tunnel located at Iowa State University. The measured effectiveness revealed that the mainstream compressibility has limited effect on film effectiveness, and the effectiveness of transonic speed flow can be studied in a relative low-speed wind tunnel. Pertinent to interior cooling of turbine blades, finally, an experimental investigation was also conducted to quantify the characteristics of the turbulent boundary layer flows over a dimpled surface. Many interesting flow features over the dimpled surfaces, such as the separation of incoming boundary layer flow at the dimple front rim, the formation and shedding of unsteady Kelvin-Helmholtz vortices over the dimple cavity, the impingement of the high-speed incoming flow onto the back rim of the dimple, and the generation of strong upwash flow over the back rim of dimple, were revealed clearly and quantitatively. This was found to correlate well with the enhanced heat transfer performance of dimpled surface design reported in previous studies

FLOW PAST DIMPLED SURFACES

Ph.DDOCTOR OF PHILOSOPH

Numerical Simulation of Convective-Radiative Heat Transfer

This book presents numerical, experimental, and analytical analysis of convective and radiative heat transfer in various engineering and natural systems, including transport phenomena in heat exchangers and furnaces, cooling of electronic heat-generating elements, and thin-film flows in various technical systems. It is well known that such heat transfer mechanisms are dominant in the systems under consideration. Therefore, in-depth study of these regimes is vital for both the growth of industry and the preservation of natural resources. The authors included in this book present insightful and provocative studies on convective and radiative heat transfer using modern analytical techniques. This book will be very useful for academics, engineers, and advanced students