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Due to the proximity of the first stage gas turbine vanes to the combustor, coolant introduced to the combustor walls interacts with the endwall film coolant and changes the vane passage flow physics. Recent results show that combustor coolant contributes significantly to cooling the endwall and vane surfaces. In this paper, the traditional combustor-turbine interface was modified to improve overall cooling performance. The performance of this new injection cooling scheme on passage fluid dynamics and surface cooling is assessed. The first of this two-part paper reports detailed experimental tests that document secondary flows and coolant transport throughout the vane passage for four combustor coolant flowrates. The experimental facility imitates combustor coolant injection and engine-level turbulence and has a modified transition duct design, called the ‘close-coupled combustor-turbine interface.’ The ‘impingement vortex’ seen in previous studies with combustor cooling appears as the dominant secondary flow. It is observed in the present study over a wide range of flowrates, confirming its tie to the combustor coolant flowrate and not the combustor-turbine interface geometry. It was found, however, that the location and size of the impingement vortex are affected by coolant flowrate. The second of this two-part paper discusses the impact of the observed secondary flows on cooling vane passage surfaces.

Research results demonstrate the heat transfer effectiveness of an impinging synthetic jet toward cooling a plane normal to it. The utility of the synthetic jet lies in that the supply of coolant comes from the device itself as an alternating jetting flow that emerges from a plenum followed by a sink flow that returns to that same plenum. Experiments reported herein were conducted with the synthetic jet driven by an oscillating diaphragm powered by a rotating cam to expel fluid from the plenum out of a single hole, then return it through the same hole. The frequency of diaphragm oscillation and the distance from the synthetic jet's orifice to the surface being cooled are varied in the test program to determine their effects on cooling performance. A numerical study agrees with the results given by the experiment and flow visualization utilizing a smoke generator supports the data and numerical results. The local, time-average Nusselt numbers were measured in the experiment using the thermochromic liquid crystal technique and air as coolant. The color display of each test case was recorded with a fisheye camera. In the case of the highest frequency and shortest distance from orifice to cooled plate, a Nusselt number of nearly 40 was achieved within the central region of the cooled plate when the Reynolds number based upon jet maximum velocity and orifice diameter was 7500 and the distance from the orifice to cooled plate was 3.2 orifice diameters.

Compared to traditional continuous jets, synthetic jets (jets with oscillatory flow such that the time-average velocity is zero) have specific advantages, such as lower power requirement, simpler structure and the ability to produce an unsteady turbulent flow that is known to be effective in augmenting heat transfer. This study presents experimental and computational results that document heat transfer coefficients associated with impinging a synthetic jet flow onto the tip region of a longitudinal fin used in an electronics cooling system. The effects of different parameters, such as amplitude and frequency of diaphragm movement and jet-to-cooled-surface spacing, are recorded. The computational results show a good match with experimental results. In the experiments, an actual-scale (1 mm jet orifice) system is introduced and, for finer spatial resolution and improved control over geometric and operational conditions, a large-scale mock-up (44 mm jet orifice) is applied in a dynamically-similar way, then tested. Results of the experiments at the two scales, combined with the computational results, describe fin heat transfer coefficients on and near the jet impingement stagnation point. A linear relationship for heat transfer coefficient versus frequency of diaphragm movement is shown. Heat transfer coefficient values as high as 650 W/m2K are obtained with high-frequency diaphragm movement. Cases with different orifice shapes show how jet impingement cooling performance changes with orifice shape.

Internal cooling and film cooling are two main cooling methods in modern gas turbines. They work together to protect the high-temperature components. This paper presents the results of a computational study on cooling performance for a flat plate with both film cooling and internal cooling using a conjugate heat transfer analysis. Three internal delivery channel geometries, smooth channel, channel roughened by square ribs, and channel roughened by crescent ribs, are studied with two film cooling geometries, cylindrical hole and sister holes. The respective conjugate cooling performances are compared. To help understand the interaction between film cooling and internal cooling, detailed flow and heat transfer characteristics are presented and discussed. Results show how overall cooling effectiveness is controlled by conjugate heat transfer of the two cooling schemes. Both film cooling effectiveness and internal cooling performance are influenced by the delivery channel geometry near the hole inlets. The sink flow effects of film cooling will enhance the heat transfer coefficient near the film cooling hole inlet, enhancing with stronger blowing ratio. At the same time, film cooling performance is affected by the internal channel as the flow inside the film cooling hole is influenced by the ribs near the hole inlets.

In this work, topology optimization was used to design a fixed-geometry fluidic diode of high diodicity, defined as the ratio of pressure drop of reverse flow to forward flow. Next, the fluidic diode was used in a valveless micropump. A three-dimensional and unsteady numerical analysis of fluid flow inside the micropump with the optimized diode was conducted by Computational Fluid Dynamics (CFD). Performance of a nozzle-diffuser type diode in the valveless micropump was also evaluated under the same conditions, for comparison. Both types of micropumps were fabricated and tested. The results show that the micropump with the designed fluidic diode can reach a flow rate of up to 33.5 ml/h, which is consistent with the simulation results and 2.2 times that of the nozzle-diffuser type micropump.

For the first time, we used a hybrid physical–chemical vapor deposition (HPCVD) method to fabricate perovskite solar cells (PSCs) based on perovskite films with both organic cations and halogen anions. A high power conversion efficiency (PCE) of 18.1% was achieved based on a mixed perovskite film of MAxFA1−xPb (IyBr1−y)3 and the efficiency of the PSCs with MAPbI3 and MAxFA1−xPbI3 films were 14.5% and 16.4%, respectively. Perovskite material components and bandgaps were precisely tuned to achieve high photoelectric conversion performance. Three different types of perovskite films employed include MAPbI3, MAxFA1−xPbI3, and MAxFA1−xPb (IyBr1−y)3 (which are also designated as MAPbI3, MA0.89FA0.11PbI3, and MA0.54FA0.46Pb (I0.94Br0.06)3 with the respective bandgaps of 1.60 eV, 1.58 eV, and 1.61 eV. The experimental results demonstrate the ability to fabricate both organic cation and halogen anion mixed perovskite films by the HPCVD method and achieve easily adjustable bandgaps. In addition, the perovskite films fabricated by HPCVD have superior surface morphology, large crystal size, and low surface roughness. Eventually, this vapor-based method will have great potential in the fabrication of large-area and flexible PSCs to promote commercial application and industrialization of future PSCs.

Flow over gas turbine endwalls is complex and highly three-dimensional. As boundaries for modern engine designs are pushed, this already-complex flow is affected by aggressive application of film cooling flows that actively interact. This two-part study describes, experimentally, the aero-thermal interaction of cooling flows near the endwall of a first stage nozzle guide vane passage. The approach flow conditions represent flow exiting a low-NOx combustor. The test section includes geometric and cooling details of a combustor-turbine interface in addition to endwall film cooling flows injected upstream of the passage. The first part of this study describes in detail, the passage aerodynamics as affected by injection of cooling flows. It reveals a system of secondary flows, including the newly-discovered Impingement Vortex, which redefines our understanding of the aerodynamics of flow in a modern, film-cooled, first-stage vane row. The second part investigates, through thermal measurements, the distribution, mixing and disruption of cooling flows over the endwall. Measurements are made with and without active endwall film cooling. Descriptions are made through adiabatic surface effectiveness measurements and correlations with in-passage velocity (presented in part one) and thermal fields. Results show that the newly-discovered impingement vortex has a positive effect on coolant distribution through passage vortex suppression and by carrying the coolant to hard-to-cool regions in the passage, including the pressure surface near the endwall.

The first stage turbine of a modern gas turbine is subjected to high thermal loads which lead to a need for aggressive cooling schemes to protect its components from melting. Endwalls are particularly challenging to cool due to the complex system of secondary flows near them that wash the protective film coolants into the mainstream. This paper shows that without including combustor cooling, the complex secondary flow physics are not representative of modern engines. Aggressive injection of all cooling flows upstream of the passage is expected to interact and change passage aerodynamics and, subsequently, mixing and transport of coolants. This study describes, experimentally, the aero-thermal interaction of cooling flows near the endwall of a first stage nozzle guide vane passage. The test section involves an engine-representative combustor-turbine interface geometry, combustor coolant flow and endwall film cooling flow injected upstream of a linear cascade. The approach flow conditions represent flow exiting a cooled, low-NOx combustor. This first part of this two-part study aims to understand the complex aerodynamics near the endwall through detailed measurements of passage three-dimensional velocity fields with and without endwall film cooling. The aerodynamic measurements reveal a dominant vortex in the passage, named here as the Impingement Vortex, that opposes the passage vortex formed at the airfoil leading edge plane. This Impingement Vortex completely changes our description of flow over a modern film cooled endwall.

This paper extends the development of film cooling for application to gas turbines. Three diameter ratios of secondary hole to primary hole (0.3, 0.5 and 0.7) are constructed in an anti-vortex hole design. Film cooling effectiveness values and heat transfer coefficients are measured by the Thermochromic Liquid Crystal technique. In-flow temperature fields over downstream planes oriented normal to the main flow are measured by traversing a thermocouple. Numerical simulations are made to compute details of the flow structure to describe underlying mechanisms. Three coolant-to-mainstream blowing ratios (0.5, 1.0 and 1.5) and two coolant-to-mainstream mass flow ratios (3.43% and 5.15%) are tested. The anti-vortex hole design reduces the deleterious effects of the kidney vortex pair generated at the emersion point of the coolant jet into the passage, enlarges the film coverage, and finally improves film cooling effectiveness. The anti-vortex hole with larger secondary holes usually provides higher film cooling effectiveness.

New plasma actuators designed for enhanced flow control authority are made by increasing asymmetry of thrust during the Dielectric Barrier Discharge (DBD) actuation cycle. This is done by a change of circuitry and by adding a semi-conductive layer on top of the dielectric surface, both for effective discharging of the dielectric. Compared to the conventional sinusoidal waveform driven plasma actuators, the new designs increases the thrust by about 70% when operating at the same frequency and voltage. Measurements indicate that increases in conductivity of the semi-conductive layer lead to increasingly higher thrust.