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A flap can be used to control wing camber and as a high-lift device. A convex corner is a simplified model of the upper surface of a flap. At transonic speeds, shock-induced boundary layer separation (SIBLS) occurs at greater freestream Mach numbers and deflection angles. This results in energy losses and a reduction in aerodynamic performance. This study installs ramp-type vortex generators (VGs) upstream of a convex corner, and the effect of the height of the VG on SIBLS is determined. As the height of the VG increases, the magnitude of the mean surface pressure upstream of the corner increases and downstream expansion decreases, which results in a reduction in lift. A reduction in peak surface pressure fluctuations, the separation length, and the frequency of shock oscillation is also determined. For flow control and lift enhancement, micro-VGs are more effective. [ABSTRACT FROM AUTHOR]

Solar panels mounted on the roof of a building or ground are often vulnerable to strong wind loads. This study aims to investigate wind loads on solar panels using computational fluid dynamic (CFD). The results show good agreement with wind tunnel data, e.g. the streamwise distribution of mean surface pressure coefficient of a solar panel. Wind uplift for solar panels with four aspect ratios is evaluated. The effect of inclined angle and clearance (or height) of a solar panel is addressed. It is found that wind uplift of a solar panel increases when there is an increase in inclined angle and the clearance above ground shows an opposite effect. [ABSTRACT FROM AUTHOR]

The characteristics of flow over rectangular cavities have been well documented. However, few studies have considered cylindrical cavity flows. For compressible cylindrical cavity flows, the type of cavity flowfield is dependent on the diameter-to-depth ratio ( D / H ), which is similar to the length-to-depth ratio for a rectangular cavity flow. For an open-type cavity flow ( D / H ≤ 6.14 ), there is a slight upstream influence and uniform static pressure distributions are observed inside the cavity; a small adverse pressure gradient ahead of the rear face and a downstream expansion. The leading- and rear-edge expansions are more significant for transitional- ( D / H = 8.60 – 21.00 ) and closed-type ( D / H = 43.00 ) cavities. The amplitude of surface pressure fluctuations increases toward the rear face, for all of the test cases, whereas an additional peak near the middle of cavity floor is observed for a closed-type cavity. Notably, the effect of freestream Mach number is pronounced only on the amplitude of peak pressure fluctuations near the rear wall. Similarities between a cylindrical cavity and a rectangular cavity for a compressible flow are also highlighted in this study. [ABSTRACT FROM AUTHOR]

Experiments are performed to determine the characteristics of a compressible flow over yawed rectangular cavities for Mach numbers of 0.64, 0.70, and 0.83. The cavity’s length-to-depth ratio varies from 4.43 to 21.50 and the length-to-width ratio is unity. The yaw angle is 0°–45°. The upstream compression and downstream expansion near the front and rear corners of a cavity decrease when the value of the yaw angle increases. The amplitude of the fluctuating pressure is a maximum for an open cavity with a yaw angle of 15°. An increase in the yaw angle results in a reduction in the pressure fluctuations for both open and transitional cavities. In the span-wise direction, variations in the mean and fluctuating pressure are less significant than those in the chord-wise direction. The oscillating frequency of resonance varies slightly with the yaw angle, but the amplitudes for the power spectral density are significantly reduced when the yaw angle is larger than 30°. For lower Mach numbers, the lower mode plays an important role in self-sustained oscillations for an open cavity when there is an increase in the yaw angle. [ABSTRACT FROM AUTHOR]

Experiments were performed to investigate a transonic, turbulent boundary layer over a bi-convex corner. The total turning angle η ranged from 10 deg to 17 deg. In subsonic expansion flows, the presence of a bi-convex corner results in a decrease in local peak Mach number M peak and the amplitude of peak surface pressure fluctuations ( σ p / p w ) max . There is a delay in transition from subsonic to transonic expansion flows. A dual expansion is observed in transonic expansion flows. Shock structure, boundary-layer separation and ( σ p / p w ) max were dependent on freestream Mach number M , first turning angle η 1 and η . The length of the first corner L 1 also plays an important role. An increase in L 1 results in less flow expansion, while a decrease in the amplitude of ( σ p / p w ) max is associated with a shorter L 1 . [ABSTRACT FROM AUTHOR]

Abstract: Liquid-fueled pulse detonation engines must complete the process of feeding, mixing, and purging in milliseconds. Such an engine is extremely sensitive to the Sauter mean diameter (SMD – must be less than 10μm) and particle size distribution of the fuel, requirements which are difficult if impossible for most fuel injectors to achieve. This study selected an injector from a direct injection engine and used the aviation fuel JP-8. Utilizing a wide range of operation pressure and duration time, the injection timing and equivalence ratio could be accurately controlled with good response time. The results of the experiment indicate that an SMD of less than 10μm can be achieved with a fuel pressure greater than 8MPa. This condition, however, resulted in an overly long injection penetration. This study further incorporated the concept of flash boiling to derive a smaller SMD. However, this causes carbon deposition to occur due to cracking or thermal reaction. To circumvent this phenomenon, this study established a deoxygenation device to mitigate oxidization, further investigating the influence of heating temperature on the generation of deposition. The results of spray distribution indicated that when the fuel is heated to 100°C, only 6MPa is necessary for achieving fuel droplet characteristics favorable for detonation. Regarding deoxygenation, the results were most significant in fuel heated to 500°C. [Copyright &y& Elsevier]

Abstract: Previous studies on solar water heaters have mainly focused on the thermal efficiency of various types of solar collectors, and there has been limited work done on the aerodynamic characteristics of solar collectors or their supporting structure. However, typhoons are among the natural hazards that have a costly impact on residential construction and solar water heaters are usually installed on the flat roofs of buildings for hot water production. Thus, the safety of solar water heaters under severe wind load during typhoon season is a critical issue in the promotion of solar water heaters. In this study, an experimental program was conducted to examine the aerodynamic characteristics of solar collector models (residential and large-scale solar water heaters). The unit sectional uplift coefficient with or without a guide plate is also addressed. Measurements of mean longitudinal and spanwise surface pressure were performed. The data show that the presence of a water storage tank (or a horizontal cylinder) tends to reduce the suction force on the upper surface within the first half of the tilt flat panel (solar collector). Stronger negative longitudinal differential mean pressure is observed for the test case of a tilt flat panel only, which corresponds to strong wind load. The inverted U-shape of mean spanwise pressure distributions is also noted. With a guide plate, less wind load and more uniformity of spanwise differential mean pressure distributions are associated with a larger projected area of a guide plate on the lower surface of a tilt flat panel. This is essentially attributed to the attenuation of corner vortices and a decrease in uplift force. [Copyright &y& Elsevier]

Presents information on a study which examined the characteristics of rectangular cavity flows of airplanes. Significance of cavity flow to aerodynamic component; Experimental technique; Results and discussion.

An objective approach to determine a dataset from which a correlation model of solar diffuse fraction is fitted and tested is proposed. A typical meteorological year (TMY) of global radiation data that is measured in Tainan, Taiwan over 10 years (2011–2020) is used to construct the training dataset and the remaining data (90% data base) is used as a test dataset. Two multiple-predictor and one single-predictor correlation models for the hourly diffuse fraction are developed by using more theoretically rigorous techniques for determining the breaking points for segmentation (excluding the modified Boland-Ridley-Lauret (BRL) model) and how many significant predictors required in each segmented interval for the regression model with piece-wise linear multiple-predictor correlation. The performance of each developed correlation model is superior to that of the existing same-type model using a part (one year or two years) of the same data base. The re-modeled piece-wise linear multiple-predictor correlation model has the best long-term performance of the three developed correlation models. The modified BRL model on basis of the TMY data is second. The re-modeled Liu-Jordan-type (single predictor) model allows real time prediction and has a simpler form than the other two models but prediction accuracy is inferior. [ABSTRACT FROM AUTHOR]

This study determines the energy usage pattern for Penghu, which is an island in the Taiwan Strait, for which electricity is the major energy source. There is an increase in electricity consumption as the number of inhabitants and tourists increases. Water supply from desalination plants represents another major electricity demand. To reduce energy consumption and carbon emissions, subsidy programs are used to encourage the use of LED lighting and energy-efficient appliances (air conditioners and refrigerators), but not for common appliances, such as chest freezers. Abundant solar radiation in summer and the northeast monsoon in autumn/winter make Penghu an ideal location to take advantage of solar energy and wind power. An undersea cable between Penghu and Taiwan is now available and can be used to stabilize the isolated grid system in Penghu. The target for a low-carbon island can be achieved by installing PV systems and onshore and offshore wind turbines to fulfill the energy demand for the tourism industry. [ABSTRACT FROM AUTHOR]

Government intervention in the form of financial incentives is crucial for translating customer choice into a larger market share for solar thermal applications. The lengthy subsidy programs for solar water heaters in Taiwan have expanded the local market. On a remote island (Kinmen County), the area of solar collectors that are installed per 1000 inhabitants is 192.9 square meters. This study investigates a market-driven mechanism in terms of disposable income, household structure, building type and financial viability. The dual subsidy programs appear to have distorted the local market. The cumulative energy savings for solar water heaters that are installed is misleading because the systems are over-designed and there is a high replacement rate (or shorter service period). [ABSTRACT FROM AUTHOR]

A numerical study of the anomalous intensification of the turbulent heat transfer is performed for the initial hydrodynamic section of a long flat plate with a single row dense package of 16 inclined Oval Trench Dimples (OTD). Multiblock overlapping grids are used to solve Reynolds-Averaged Navier-Stokes (RANS) equations in the framework of VP2/3 in-house code. Firstly, applicability of RANS approach is confirmed by thorough comparison against the experimental measurements of the pressure distributions for a single inclined OTD mounted on a flat plate. Then, the dense package of OTD with the inclination angle of 60° is compared against Spherical Dimple (SD) at the same Reynolds number of 6000 based on the trench width and for the same trench depth and relatively high density of dimples. For OTD a progressive increase of the pressure drop is observed between the zone of deceleration of the free flow and the zone of low pressure near the inlet of spherical segments, where a tornado-like vortex is developed. Moreover, a gradual amplification of the reverse secondary flow is observed for OTD resulting in the minimum relative friction coefficient of −4 and the maximum relative Nusselt number of 4.4. Finally, acceleration and substantial thinning of the boundary layer above the upstream part of the OTD are observed. A new type of energy-efficient structured surfaces ready for additive technologies is proposed and justified for heat exchangers. • A new type of energy-efficient structured surfaces for heat exchangers is proposed and justified. • Abnormal turbulent heat enhancement in inclined oval-trench dimples on the flat plate is analyzed. • An extraordinary pressure difference between the zones of deceleration and rarefaction during a vortex generation is found. • Progressive intensification of the reverse, secondary and wall normal flows in the inclined dimples is outlined. • Cooling the inclined oval-trench dimples, acceleration and thinning of the boundary layer above it established. • The superiority of inclined dimples over spherical ones in terms of thermal and thermohydraulic efficiency is confirmed. [ABSTRACT FROM AUTHOR]