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Gear faults contribute to a significant portion of failures in wind turbine system. As such, condition monitoring and fault detection of these components assist in maintenance scheduling; hence, preventing catastrophic failures of the gearbox. This paper introduces a new hybrid fault detection approach to detect gear faults in wind turbines. to accomplish this task, vibration signals are collected and used to extract various time-domain features. Next, a Dynamic Principle Component Analysis (DPCA) is adaptively employed to identify failure dynamics by reducing the time-domain feature dimension. Following that, a Support Vector Machine (SVM) is implemented to detect and isolate gear faults. Experimental test studies with ten-year historical data of three wind farms in Canada are conducted. Test results indicate that the proposed hybrid approach performs superior compared to DPCA using Multilayer Perceptron (MLP) Neural Networks (NNs).

Air accumulator is a critical component in Underwater Compressed Air Energy Storage systems and Buoyancy Energy Storage systems. In order to bridge the gap between the CFD simulations and experiment verification of flow around air accumulator, in this study, the force characteristics and flow structures around a balloon-shaped air accumulator bluff body model have been investigated using a computational-experimental dual prong method for the first time. The three-dimensional Unsteady Reynolds Averaged Navier-Stokes (URANS) closure is achieved through the k-ω SST turbulence model in FLUENT. The force characteristics and flow structures are measured in a low-speed closed-loop wind tunnel to verify the simulation results. The free end and shape effects are investigated by comparing the flow structure of three different but interconnected bluff bodies at the equivalent Reynolds number of 7.0 × 104. The results show that the k-ω SST turbulence model can correctly predict the time-averaged force characteristics of the balloon-shaped bluff body and flow structures in the wake. Besides, the distinct vortex structures are induced due to the free end and tapered shape effects.

A data driven exergy analysis has been conducted for the first known grid connected Underwater Compressed Air Energy Storage facility, located in Toronto, Canada. Further to examining the plant through conventional exergy analysis, results were enhanced by splitting exergy destruction rates into avoidable and unavoidable, as well as endogenous and exogenous parts via advanced exergy analysis. The conventional exergy analysis showed that under real operational conditions, the exergy destruction ratio was 47.1%, while under the theoretical unavoidable operational conditions it could be reduced to 15.9%. The overall outcome of the conventional exergy analysis was confirmed by the advanced exergy analysis, the details, however, were quite different. The results of advanced exergy analysis assigned the improvement priority to heat exchanger 4, followed by the turbine and the stage 3 compressor. Conversely, the conventional exergy analysis indicated that the total exergy destruction of the turbine was higher than that for heat exchanger 3. The advanced exergy analysis also revealed that 76.4% of the exergy destruction was avoidable, highlighting the significant potential of the system for performance improvement.

Exergy analysis has been applied in various engineering fields. Most of these analyses have been conducted under steady-state conditions. This can be of limited use when the operation under consideration is highly transient. Such is the case for energy storage systems connected to a dynamic grid. In this work, a transient exergy analysis has been performed for the first known grid connected Underwater Compressed Air Energy Storage facility. Both conventional and advanced exergy analyses were applied. The conventional exergy analysis showed that at plant start up, the compressors have the highest exergy destruction ratio. Under real and unavoidable operational conditions, they alone are responsible for 40% and 35% of exergy destruction of the system. Under the steady-state condition, however, heat exchangers have the dominant effect with 29% and 31% exergy destruction ratios under real and unavoidable operating conditions, respectively. The advanced exergy analysis also revealed that at start up, about 82% of the exergy destruction is avoidable. By the beginning of the steady-state phase, this decreases to 75%, indicating the significant potential of the system for performance improvement. The transient exergetic analysis documented herein has wide applicability for design optimization of a variety of thermodynamic processes.

Fourier analysis is presented for 10 years of Hourly Ontario Energy Price data (2005–2015) to identify primary governing frequencies driving the price. As anticipated, a 24 h cycle was found to be most prominent each year. Simulation of the revenue generation performance of a standardized energy storage system of 1 MW power rating and 1 MWh energy capacity was completed with various charge and discharge times. The best performing operation programs are presented and discussed. Multi-cycle operation was also considered and an equation for multi-cycle yearly revenue has been defined based on a storage program performance coefficient. Overall, revenue simulations indicate that energy storage facilities are not financially viable under current market conditions without additional subsidies and payments from the grid controller.

The effect of winglet aspect ratio on the generated vortical flow over a flat surface was experimentally scrutinized in a wind tunnel using a triple sensor hot-wire. Aspect ratios of 1, 2 and 4 were considered at a Reynolds number based on winglet height of 6000 and an angle of attack of 30 degrees. A large longitudinal vortex structure was observed in the cross-stream plane. The streamwise velocity deficit at the main vortex core lessened, while that at the Upwash Region remained unaltered, with increasing aspect ratio. Moreover, the vortex moved downward and inward and its intensity decreased. The turbulence level decreased with a corresponding increase in Taylor microscale. The integral length was found to be independent of the aspect ratio but scaled with the winglet height.

The heat transfer performance of a flat plate behind a 10 mm high (h) and 20 mm long delta winglet was studied at a distance up to 30h in a wind tunnel at a Reynolds number based on h of 6000. The focus was on the role of the attack angle, which was varied from 30 to 60° in 15-degree increments. The bottom side of the flat plate was uniformly heated by condensing steam at 100 °C. Surface thermal imaging results indicated that the peak Nusselt number (Nu) increases with the attack angle, and this augmentation was attributed to the larger share of the transverse vortex at the larger attack angles. Peak Nu dropped sharply in the near wake (X/h

This paper investigates the use of a vertical coaxial borehole heat exchanger (BHE), focusing on those consisting of standard geothermal piping material, as a component in a ground-source heat pump system. The results of a lab-scale experiment are used to verify the trends exhibited by a recent semi-analytical model, referred to as the composite coaxial (CCx) model, considering short-term behavior when laminar flow is experienced in the annular space of a coaxial heat exchanger. The discussion on pipe sizes is then expanded upon using the suggested model along with a modified design procedure to compare the performances realized by an example heat pump. A comparison is made here between configurations having various nominal inner pipe diameters while maintaining the same outer pipe. The results of the analysis show that increasing the inner pipe diameter, within the verified limit of the composite coaxial model, will reduce the required length of heat exchanger and increase the overall coefficient of performance realized by the heat pump.

Sustainable and cost-effective water treatment systems are critical elements to developing nations. In India, the human population is escalating while the water availability is lagging behind. An adaptable, affordable, and sustainable wastewater treatment system powered by wind/solar energy is proposed based on proven theory and technology. A household in India is singled out to illustrate the workings of the proposed system, where the wastewater is recirculated through a hybrid of water purifiers powered by solar/wind energy. The system demonstrated here is specifically designed for small-scale applications, i.e., for a single household. The solar still has been divided into four stages. Partial vacuum is created inside the still so as to obtain boiling point temperatures of 70 °C, 67 °C, 62 °C and 50 °C in the four stages. Dhanbad, India 23.79°N, 86.43°E, with an average solar intensity of 850 W/m 2 for 6 h a day, has been used for this study. A lumped parameter mathematical model was developed for this study. With an aperture area of 2.5 m 2 , the total amount of water distilled is found to be 43.3 kg/day. The system proposed is more efficient than existing systems as it is able to achieve efficiencies as high as 53%. The effect of wind speed on distillate output yield has also been discussed.

Floating offshore wind farms (FOWF) with advanced adiabatic compressed air energy storage (AA-CAES) are thermodynamically scrutinized to evaluate if the compressed air is better stored underground or underwater. The corresponding energy efficiency is deduced based on an exergy analysis that details the exergy destruction of each system. The effects of key parameters such as storage and expansion pressures are examined parametrically. It is revealed the underwater compressed air energy storage has a higher efficiency and exergy density. These advantages tend to diminish beyond a critical storage pressure.

This paper presents concepts and considerations for integrating a Buoyancy Energy Storage System with a utility scale wind turbine and the Ontario, Canada energy market is used as a case study. Using derived characteristic equations of operation, a Buoyancy energy system is sized for storage of 1 MWh of electrical energy. Practical considerations of float and equipment selection are discussed and hydrodynamic drag losses calculated for the desired float velocity range. Round-trip efficiency is estimated based on calculated losses. Power generation data from a 2.3 MW wind turbine is presented along with the historic energy purchase price data for Ontario in 2015. Total revenue and net revenue resulting from storage is calculated based on historic data and a developed bi-diurnal storage program. Open water testing of a small scale system was conducted in Lake Huron which confirmed steady state operation of the system under sufficient loading

The turbulent strain rate generated by a pair of 25.4 mm tall and 12.7 mm wide (W) rectangular strips at a Reynolds number based on the strip width of 8500 was measured using a 3D hotwire probe in a wind tunnel. The strips were placed side-by-side separated by 3 W, 2 W, and 1 W. The convective heat transfer enhancement, denoted by the normalized Nusselt number (Nu/Nu0), was correlated with turbulence fluctuation, Taylor microscale, turbulent strain rate and integral-Taylor scale ratio. With the effects of both turbulence fluctuation and eddy scale incorporated, the turbulent strain rate correlated most strongly with Nu/Nu0, with an R-square value of 0.82. Comparatively, the R-square for Nu/Nu0 - velocity fluctuation and Nu/Nu0 - Taylor microscale were 0.77 and 0.64, respectively. Furthermore, the turbulent strain rate was found to have the most significant impact on heat transfer augmentation, more so than the individual effects of turbulent fluctuation and Taylor microscale.

Underwater energy storage provides an alternative to conventional underground, tank, and floating storage. This study presents an underwater energy storage accumulator concept and investigates the hydrodynamic characteristics of a full-scale 1000 m3 accumulator under different flow conditions. Numerical simulations are carried out using an LES turbulence model. Time-averaged and transient flow structures and force characteristics are analyzed. The results show that the vortex structures are complex and scale-rich, but periodic vortex shedding can still be identified. The shedding frequency is consistent with the fluctuation of the lift force in the cross-flow direction. A dominant Strouhal number of 0.18 is found. The mean drag and lift coefficients stabilize at 0.45 and 0.60, respectively, and are insensitive to Reynolds number variation. Modal analysis shows that the natural frequency of the accumulator falls between 27 and 48 Hz and is much higher than the vortex shedding frequency. Thus, for the accumulator model investigated in this study, the risk of vortex-induced vibration (VIV) fatigue damage is very low.

The prevailing atmospheric wind can be manipulated to enhance the convective cooling of a solar photovoltaic panel and thus its energy conversion efficiency. The transverse spacing of a delta winglet pair was examined for its role in convective heat transfer enhancement. A pair of winglets with an inclination angle of 90° and a chord/height ratio of 2 was positioned at an attack angle of 30° with respect to incoming wind at a Reynolds number, based on the winglet height, of 6300. The transverse distance was varied from 0 to 3 winglet heights in 1 winglet height increments. The Nusselt number normalized by the reference no-winglet Nusselt number was determined from the surface temperature measured by a thermal camera. The two-height-spaced winglet pair was found to lead to the largest heat convection improvement. This significant heat transfer enhancement was explained in terms of vortical flow characteristics detailed at 10 winglet heights downstream of the winglet pair, where the most potent downwash was induced when the transverse spacing was 2 winglet heights.

Compared with traditional isochoric storage of compressed air in pneumatic systems, isobaric storage possesses many advantages. In this study, a novel isobaric compressed air storage device is proposed by introducing compressed gas energy storage and a nonlinear cam transformation mechanism. The critical profiles on both sides of cam are deduced and the mathematical model of a typical pneumatic system is established under different control modes. A parametric analysis is also conducted to reveal how the energy-saving performance can be affected by several factors. The results show that this new isobaric compressed air storage device presents favorable constant-pressure characteristic and energy-saving performance. With a pneumatic system working pressure of 0.4 MPa, 18% energy savings can be achieved and the compressed air pressure is stable within 2.14%. The working pressure of system has a significant effect on the energy-saving performance and the energy-saving rate decreases with the increasing working pressure. The proposed novel isobaric compressed air storage device provides a new way to reduce pressure and energy consumption of pneumatic systems.

Employing turbulence generators, such as rectangular flexible strips, is a simple and effective approach to enhancing forced convection. In the current study, 12.7 mm wide rectangular flexible strips (with thickness of 0.1 mm, 0.2 mm and 0.25 mm, height of 25.4 mm, 38.1 mm and 50.8 mm, transversal spacing of 12.7 mm, 25.4 mm and 38.1 mm) were investigated at Reynolds number (Re) of 8500 and 6000, and freestream turbulence intensity (Tu) of 0.4%, 7%, 9%, and 11%. The convective heat transfer augmentation was analyzed in terms of the normalized Nusselt number (Nu/Nu0). The relationships between the averaged Nu/Nu0 and the strip thickness, height, spacing, Re and Tu were determined using multiple linear regression. The correlations between the local Nu/Nu0 and turbulent flow parameters, including turbulent kinetic energy, downwash velocity and near surface streamwise velocity were also illustrated. The freestream turbulence intensity (Tu) had the most significant effect in augmenting the averaged Nu/Nu0, and the local Nu/Nu0 correlated best with the local ke. The maximal averaged Nu/Nu0 over 23 W downstream, within ± 1 and ± 4 strip widths cross-stream was found for Tu = 7% case and Tu = 11% case, respectively.

The vortical turbulent flow generated by a 10 mm high and 20 mm long delta winglet on a flat surface was experimentally studied in a wind tunnel. The flow field at 10 winglet heights downstream was measured using a triple wire probe at a Reynolds number of 5000, based on winglet height. Main vortex and induced vortex structures were observed in the form of the cross-stream velocity vector and the vorticity contour. Boundary layer thickness, streamwise velocity distribution, turbulence intensity and Taylor microscale were compared at the inflow and outflow regions as well as in the base flat plate case. The inflow region was postulated to have a larger potential for heat convection; since the vortex penetrated into the boundary layer, the boundary layer thickness increased, while maintaining high turbulence intensity. At the core of both the main vortex and the induced vortex, both the streamwise velocity deficit and the turbulent intensity were enhanced.

Wind Turbine power output prediction can prevent unexpected failure and financial loss, through the detection of anomalies in turbine performance in advance so operators can proactively address potential problems. This study examines common Supervisory Control And Data Acquisition (SCADA) data over a period of 20 months for 21 pitch regulated 2.3 MW turbines. To identify the most influential parameters on power production among more than 150 signals in the SCADA data, correlation coefficient analysis has been applied. Further, an algorithm is proposed to impute values that are missing, out-of-range, or outliers. It is shown that appropriate combinations of decision tree and mean value for imputation can improve the data analysis and prediction performance. A dynamic ANFIS network is established to predict the future performance of wind turbines. These predictions are made on a scale of 1 h intervals for a total of 5 h into the future. The proposed combination of feature extraction, imputation algorithm, and the dynamic ANFIS network structure has performed well with favourable prediction error levels in comparison with existing models. Thus, the combination may be a valuable tool for turbine power production prediction.

Significant heating demands are present in greenhouses to maintain suitable indoor conditions for crop growth. In an effort to implement clean energy technologies in an industry heavily reliant on natural gas, the potential of a large-scale solar collector system with seasonal thermal energy storage is explored. Both low and high-temperature borehole thermal energy storage systems are developed using TRNSYS software and their performance is compared. Systems able to cover up to 65% of the annual greenhouse heating demand are discussed with differing positive attributes. The systems are able to reduce annual CO 2 equivalent emissions by ∼220 t/Acre.

This paper uses composite cylindrical heat-source (CCS) models and typical thermal response test procedures to investigate two full-scale borehole heat exchangers (BHE); where one is a U-tube BHE, and the other, a pipe-in-pipe (coaxial) BHE. A previously developed CCS model is compared to a simplified infinite line-source (ILS) model. A time-varying heat-flux term is verified for the U-tube case, noting the error found when using the CCS model. A model is developed using a similar approach accounting for a coaxial configuration showing a root mean square error (RMSE) of less than 0.1 °C over the duration of the test.

Flow and convection heat transfer downstream of a square rib on a flat plate were experimentally investigated inside a closed loop wind tunnel. Heat transfer augmentation for the ribbed plate compared to the smooth plate (Nu/Nu0) was studied at Reynolds numbers, based on the rib’s height (H = 1 cm), of ReH = 1.3 × 103, 2.6 × 103, 5 × 103 and 6.3 × 103. The ribbed plate presented an enhancement in heat transfer (Nu/Nu0 > 1) at all studied Reynolds numbers. A trend of decreasing enhancement with increasing ReH was observed, with the largest decrease in Nu/Nu0 occurring when ReH increased from 1.3 × 103 to 2.6 × 103. The remarkable enhancement in Nu at the lowest Reynolds number (ReH = 1.3 × 103), compared to higher ReH, was presumably due to the transition of the boundary layer regime from laminar to turbulent. To investigate the effect of the rib on the flow over the surface, flow and turbulence structures were measured using an X-probe hot-wire anemometer. It appears that the turbulence generated by the rib (urms, vrms, uv ‾ ) is the most influential factor on enhancing the heat transfer from the surface. Also, the normal velocity (V) created downstream of the rib seems to be somewhat effective in extracting heat from the surface, while the streamwise velocity (U) was blocked by the rib. The energy spectra of normal velocity fluctuations showed traces of vortex shedding from the rib’s edge at ReH = 1.3 × 103.

Turbulence generators such as a 25.4 mm tall, 12.7 mm wide (W) and 0.1 mm thick rectangular flexible strip can provide a robust means of enhancing convective heat transfer. This wind-tunnel study aimed at uncovering the effect of freestream turbulence on heat convection enhancement of a flat surface by a flexible strip. The freestream turbulence was furnished by a 6 mm thick orificed perforated plate (OPP) with 57% perforation consisting of 38.1 mm diameter (D) holes. The OPP was installed at 10D, 13D and 16D upstream of the strip, to achieve 11%, 9% and 7% turbulence. The investigation was conducted at a Reynolds number based on the strip width of 6000. The convective heat transfer augmentation was analyzed in terms of Nusselt number with respect to the reference no-strip case (Nu/Nu0). The flow turbulence was characterized with the help of a 3D hotwire probe. The freestream turbulence is found to diminish the flexible-strip induced Nu/Nu0 significantly. This is principally because Nu0 increases considerably with increasing freestream turbulence. It is of practical significance that the flexible strip always increases Nu, and this improvement is largest with respect to an otherwise ‘laminar’ freestream.

This paper presents an alternate method of underwater energy storage utilizing an object's inherent buoyancy as a means for storage known as buoyancy battery energy storage (BBES). Utilizing a simple pulley, reel and float mechanism, energy can be stored for an indefinite period of time. Governing equations of charge and discharge are defined through application of Archimedes principle of buoyancy for an ideal system. Inefficiencies, losses as well as potential application configurations are presented and discussed. Basic experimental validation was completed to confirm system properties of constant discharge force with respect to both float position and storage duration.

The aerodynamic interaction of vertical axis wind turbines in several array configurations was studied by conducting a series of wind tunnel measurements. Four configurations of two- and three-turbine arrays were tested and their results were compared with that of the isolated reference case. Two pairs of counter-rotating and co-rotating vertical axis wind turbines were tested where the free-stream wind was perpendicular to the two side-by-side turbines. The counter-rotating configuration resulted in a slight improvement in the aerodynamic performance of each turbine compared to the isolated case, while the co-rotating installation caused a slight performance reduction of turbines at some free-stream velocities. Several measurements were also performed for three-turbine arrays with different spacing where a vertical axis wind turbine was operating downstream of a counter-rotating pair, perpendicular to the free-stream wind. An enhancement in the aerodynamic performance of the downstream turbine was observed in almost all arrays and at most tested wind speeds. For the array spacing studied, the optimum range of the streamwise distance of the downstream turbine from the counter-rotating pair and the spacing between the pair was determined to be about three and one rotor diameters, respectively.

A 2 MW underwater compressed air energy storage (UWCAES) system is studied using both conventional and advanced exergy analyses. The exergy efficiency of the proposed UWCAES system is found to be 53.6% under the real conditions. While the theoretical maximum under the unavoidable condition is 84.3%; showing a great potential for performance improvement. Even though there are quantitative differences between conventional and advanced results, both show that the final compressor stage has the highest potential for improvement. The advanced exergy analysis reveals the real improvement potential of the UWCAES system. Further, it is revealed that the interactions between system components are complex but not very strong. Subsequently, the total exergy efficiency may not necessarily increase by improving the performance of the components individually.

The possibility of bridge stay cables experiencing violent dry inclined cable galloping raises great concern in the engineering community. Numerous experimental and analytical studies have been conducted to investigate this phenomenon, most of which were in the context of steady wind past a rigid cylindrical body. Real stay cables however, are generally long and flexible. They are exposed to more “broad” range of atmospheric boundary layer type of wind velocity profile which is also unsteady and turbulent by nature. To better understand the physics underlying this type of wind-induced cable vibration and to elucidate various contributing factors, a more realistic analytical model which is capable of addressing the above elements is imperative. In the current paper, a three-dimensional aeroelastic model is proposed to study the aerodynamic response of an inclined and/or yawed slender flexible cylindrical body subjected to unsteady mean wind, with practical application to wind-induced vibrations of bridge stay cables under no precipitation condition. The non-linear aerodynamic forces derived in the present study are combined with the cable free vibration equations available in literature to obtain the equations of motion for the wind-induced vibration of stay cables, which are solved numerically by an explicit finite difference scheme. The proposed three-dimensional aeroelastic model and numerical solution technique are validated by comparing the predicted cable free vibration responses with existing data in the literature. The mechanism which triggers dry inclined cable galloping and the required conditions for its growth are explored. In addition, the impact of different initial conditions and various unsteady mean wind scenarios on this violent cable motion are investigated. Results show that the occurrence of dry inclined cable galloping is associated with an opposite-phase relation between the relative wind speed and the aerodynamic force along the direction of cable motion in the critical flow regime. The cable would respond most violently should it be exposed to uniformly distributed steady wind in the critical Reynolds number range for a sufficiently long duration. The presence of multi-mode oscillation in a cable prior to its exposure to the critical flow condition would lead to a considerable reduction in cable response. Furthermore, the boundary layer type velocity profile would have a sizable impact on the cable aerodynamic response provided only a portion of the cable is subjected to the critical flow condition, and the unsteadiness in wind is found to have a stabilizing effect on cable aerodynamic response.

Energy storage technologies are essential for the mainstream realization of renewable energy. Underwater compressed air energy storage (UWCAES) is developed from mature compressed air energy storage (CAES) technologies and retrofitted to store offshore renewable energy. Existing UWCAES technologies, however, usually operate at off-design conditions when handling fluctuating and intermittent renewable energy, which compromises the round-trip exergy efficiency. To increase efficiency, a multi-level UWCAES system is proposed. The results show that the exergy efficiency of the multi-level UWCAES system varies from 62% to 81% in different working modes. The exergy efficiency tends toward 62% when more energy is stored in the CAES subsystem and approaches 81% when more energy is stored in the design-integrated battery pack.

A pair of 12.7 mm wide (W) and 25.4 mm tall rectangular flexible strips made of 0.1 mm thick aluminum sheet was employed to enhance convective heat transfer from a flat surface in a closed-loop wind tunnel. The strip pair was placed side-by-side with a spacing of 1W, 2W and 3W. The incoming wind velocity was fixed at 10 m/s, resulting in a Reynolds number based on the strip width (ReW) of 8.5 × 103. The heat transfer enhancement was represented in terms of the Nusselt number with respect to the reference Nusselt number in the absence of the strip pair (Nu/Nuo). A triple-sensor hotwire probe was employed to characterize the flow characteristics when the plate was unheated. Particularly strong vortex-vortex interactions, a large downwash velocity and intense flow fluctuations were obtained behind the 1W-spaced strip pair. These contributed to better mixing and transport of the thermal energy. The 1W-spaced strip pair generated the highest Nu/Nu0 values. Nu/Nu0 of approximately 1.50 was achieved at the middle of the strip pair at X=9W. At this location, the pairs separated by 2W and 3W resulted in Nu/Nu0 value of around 1.26 and 1.17, respectively. The 1W-spaced strip pair also produced the largest span-averaged Nu/Nu0.

A 0.1 mm thick and 12.7 mm wide (W) rectangular flexible strip is experimentally investigated for its effectiveness in boosting the convective cooling from a heated flat plate in a wind tunnel. Three strip height, 25.4 mm, 38.1 mm and 50.8 mm, were explored at a 10 m/s wind, and a Reynolds number of 8500, based on the strip width. The heat transfer results are expressed in terms of Nusselt number normalized by the corresponding unperturbed reference case (Nu/Nuo). To uncover the physics behind the heat transfer enhancement, the turbulent flow characteristics were detailed via a 3D hotwire probe. The 25.4 mm-high strip generated vortex structures closest to the surface, and the largest near-surface-downwash velocity. These attributes result in a better mixing, and thus, heat removal. Therefore, the 25.4 mm-high strip provides the highest Nu/Nuo, with a peak value of approximately 1.76 at 9 W downstream, 0.26 larger than that of the 50.8 mm-high strip.

Recent advances in additive manufacturing (AM) and Fused Material Deposition (FMD) techniques have resulted in the commercialization and popularization of what is commonly known as 3D printing. Small wind turbine technology stands to benefit greatly from this technology when considering turbines intended for disaster relief and rural electrification. With the appropriate design, wind turbines could be rapidly manufactured (printed) and assembled on-site at an as needed basis without additional tooling beyond a 3D printing machine and printing filament. This paper examines the design considerations of such a wind turbine including material properties, reinforcement techniques, integration of non-printed components, printed component design and print optimization. A rapid manufacture-able design is presented of vertical axis configuration. Conclusions are drawn as to the viability and practicality of 3D printed wind turbines and opportunities for future work are identified.

This paper studies the effects of pre-tension on flow-induced vibration of a flexible cylinder with two degrees of freedom in a towing tank. A 0.45 m section of Tygon tubing with an outer and inner diameter of 7.9 mm and 4.8 mm respectively, was employed as a flexible test model, the mass ratio and aspect ratio of which is 0.77 and 57, respectively. It was towed from rest up to 0.8 m/s before slowing down to rest again over a distance of 1.6 m in still water with three cases of pre-tension from 0 to 8 N. The Reynolds number based on the cylinder’s outer diameter spanned from approximately 780–6300 while the reduced velocity ranged from 2 to 16. Emphasis was on revealing the possible relationship between pre-tension and response amplitude as well as the frequency. The vibration amplitude and frequency obtained during the brief constant towing speed were quantified and expressed in terms of reduced velocity. Narrowed lock-in bandwidth and reduced response amplitude were observed. The findings from this set of experiments are compared to the existing knowledge in the literature.

The performance of ground source and surface water heat pumps relies greatly on the heat transfer efficiency throughout the ground loop configuration. Typically these are vertical loops and consist of two pipes connected by a U-Bend at the bottom end. The U-Bend section generates vortical structures and turbulence, enhancing the heat transfer process. Two parameters that affect the flow turbulence and vortical structures are the Reynolds number and the Dean number. The isolated effects of the Reynolds and the Dean number are studied. It was found that while the Reynolds number has the greater effect on the average heat flux of the system; the Dean number’s influence on the heat flux is greater in the curved section of the pipe. The large vortex structures can last for many diameters downstream of the U-Bend. For the high Reynolds number flow it was shown that increasing the Dean number significantly enhances the longevity of vortex structures. This indicates that enhancing the Dean number in an already turbulent flow will further augment the heat transfer process.

A full-scale three-dimensional simulation was conducted to investigate structural response of an underwater compressed air energy storage (UWCAES) accumulator to the hydrodynamic loads at Reynolds number of 2.3 × 10 5 . The accumulator was assumed to be spherical, non-distensible and fixed to the bed of a water body via a cylindrical homogeneous isotropic elastic support. The simulation was carried out for three different supports with aspect ratios AR of 5, 10 and 20 where AR was defined as the ratio of the length to the diameter of the support. The effects of the aspect ratio on the frequency and amplitude of the vibrations of the solid structure induced by hydrodynamic loading were investigated. It was observed that the amplitude of the vibrations increases with the aspect ratio of the support, whereas the frequency decreases. The displacement of the spherical accumulator was illustrated on the X – Y plane for each case.

The effect of external free-stream turbulence on the aerodynamic performance of a vertical axis wind turbine was studied via wind tunnel testing under controlled levels of wind turbulence. Three levels of turbulence intensity of 5%, 7.5%, and 10% were generated upstream of the vertical axis wind turbine using a grid turbulence generator. Turbulent flows generated downstream of the grid had uniform mean flow profiles, free of any wind shear effects. Turbulence characteristics were reported in terms of turbulence velocity fluctuations, probability density function, and power spectral density. It is demonstrated that the turbulence generated downstream of the current grid is quasi-isotropic. Results show that the turbine power output was substantially increased in the presence of the grid turbulence, even though the increase in turbine power coefficient due to the effect of grid turbulence was small at the same tip speed ratios. Among grid generated turbulent flows, the increase in power output with increasing turbulence intensity was marginal. Moreover, the self-starting behavior of the vertical axis wind turbine is improved under the influence of external free-stream turbulence.

The effect of external free-stream turbulence was investigated experimentally in the near-field of a wing-tip vortex. A free-stream turbulent flow with 4.6% turbulence intensity was created with the aid of a grid turbulence generator, while the turbulence intensity in the base flow case with no grid was approximately 0.5%. The experiments were conducted in a closed-circuit wind tunnel while a dynamic force transducer was used to measure the aerodynamic forces on a NACA 0015 wing section in the range of 0° to 25° angle of attack. The wing section with a semi-span aspect ratio of 5.4 spanned approximately half height of the wind tunnel section and fixed vertically to the load cell at the base. Hot-wire anemometry was used to measure the velocity field downstream of the wing at crossflow planes of x / c = 0.1 , 0.42 , 0.77 and 1.03 while the Reynolds number and angle of attack were set at 1.6 × 10 5 and 10°, respectively. The results of aerodynamic force measurement for the no-grid case agree fairly with other experimental and analytical works. In addition, circumferential velocity and circulation profiles inside the vortex flow-field fit well with analytical expressions proposed by others. The crossflow velocity contours show that the free-stream turbulence tends to increase the vortex diffusion at x / c = 0.77 and 1.03 . The inboard and upward movement of the tip vortex downstream of the wing was not significantly affected by the introduction of free-stream turbulence, while external free-stream turbulence increases the turbulence intensity peak. External turbulence also increased the circumferential velocity and vortex circulation with respect to the streamwise distance at radial locations far from the vortex center.

A power generating energy storage system is presented. The proposed self-powered energy storage technology (UWCAES–VHE) is a hybrid of Underwater Compressed Air Energy Storage (UWCAES) and the Vortex Induced Vibration Aquatic Clean Energy (VIVACE) converter invented by Bernitsas and Raghavan [1] to harness Vortex Hydro Energy (VHE). The present technology significantly improves the roundtrip efficiency of conventional UWCAES. Through this hybridization, the energy conversion efficiency of the VIVACE converters performing as the accumulator–converters of the UWCAES–VHE is expected to be higher than that of the conventional VIVACE converters. It is further demonstrated that the round trip efficiency of the UWCAES–VHE and the VHE conversion efficiency of the VIVACE are linearly related. UWCAES–VHE and conventional UWCAES are quantitatively compared.

This paper presents the findings from a multi-objective genetic algorithm optimization study on the design parameters of an underwater compressed air energy storage system (UWCAES). A 4 MWh UWCAES system was numerically simulated and its energy, exergy, and exergoeconomics were analysed. Optimal system configurations were determined that maximized the UWCAES system round-trip efficiency and operating profit, and minimized the cost rate of exergy destruction and capital expenditures. The optimal solutions obtained from the multi-objective optimization model formed a Pareto-optimal front, and a single preferred solution was selected using the pseudo-weight vector multi-criteria decision making approach. A sensitivity analysis was performed on interest rates to gauge its impact on preferred system designs. Results showed similar preferred system designs for all interest rates in the studied range. The round-trip efficiency and operating profit of the preferred system designs were approximately 68.5% and $53.5/cycle, respectively. The cost rate of the system increased with interest rates.

A two-degree-of-freedom aeroelastic model is proposed to study wind-induced response of bridge stay cables in the context of a rigid circular cylinder model oscillating in an arbitrary orientation with respect to the oncoming unsteady flow. Compared to the existing analytical models and wind tunnel studies, the proposed model can take into account the unsteady characteristics of natural wind and predict the evolving history of cable response. The validity of the proposed model is verified by the results from an earlier wind tunnel study. The rationality of defining a cable aerodynamic stability criterion using solely the Ur–Sc relation is discussed. Two different unsteady wind models are used to investigate the impact of flow unsteadiness on the wind-induced response of stay cables. A case study is presented to evaluate the aerodynamic behavior of a real bridge stay cable in unsteady/turbulent natural wind. Results show that while the emergence of critical Reynolds number regime is crucial for the onset of dry inclined cable galloping, the spanwise correlation of aerodynamic forces acting on a cable and the sustained duration of critical flow condition are the determining factors for the continuous growth of unstable cable response and the eventual occurrence of this type of aerodynamic instability.

Employing an appropriate turbulence generator is a simple and effective means to boost convective heat transfer. In this study, a flexible 12.7 mm wide by 38.1 mm tall rectangular strip positioned normal to the freestream is explored for its effectiveness in enhancing the convective cooling of a heated plate in a wind tunnel. The effect of the flexibility of the strip is of particular interest. Thus, strip thicknesses of 0.1, 0.2 and 0.25 mm are investigated at a wind velocity of 10 m/s, a Reynolds number based on the strip width and freestream velocity of 8.5 × 103. The resulting Nusselt number augmentation with respect to the unperturbed reference case is explained in terms of the turbulent flow characteristics detailed via a triple-sensor hotwire. A higher velocity toward the heated plate is detected behind the 0.1 mm-thick strip, contributing to the most effective heat transfer performance, approximately 0.1 higher than that associated with the 0.25 mm-thick strip in terms of the normalized Nusselt number.

A torus could replace an orifice flow meter with the benefit of a lower pressure loss. The flow structure of a torus with an aspect ratio of three was scrutinized in a wind tunnel. This study details the vortical structures at 5, 7, 10 and 15 core diameters downstream of the torus. This paper also studied the drag coefficient of the torus. The Reynolds numbers based on core diameter and free stream velocity are 9 × 103, 1.2 × 104 and 1.5 × 104. Of particular interest is the resulting Strouhal number through the opening. This was evaluated through detailed flow turbulence characterization.