CFD analysis of the angle of attack for a vertical axis wind turbine blade

The Angle of Attack (AOA) of the Vertical Axis Wind Turbines (VAWTs) blades has a dominant role in the generation of the aerodynamic forces and the power generation of the turbine. However, there is a significant uncertainty in determining the blade AOAs during operation due to the very complex flow structures and this limits the turbine design optimization. The paper proposes a fast and accurate method for the calculation of the constantly changing AOA based on the velocity flow field data at two reference points upstream the turbine blades. The new method could be used to calculate and store the AOA data during the CFD simulations without the need for extensive post-processing for efficient turbine aerodynamic analysis and optimisation. Several single reference-points and pair of reference-points criteria are used to select the most appropriate locations of the two reference points to calculate the AOA and It is found that using the flow data from the two reference points at the locations 0.5 aerofoil chord length upstream and 1 chord away from each side of the aerofoil can give most accurate estimation across a range of tested AOAs. Based on the proposed AOA estimation method, the performance of a fixed pitch and the sinusoidal variable pitch VAWT configurations are analysed and compared with each other. The analysis illustrates how the sinusoidal variable pitch configuration could enhance the overall performance of the turbine by maintaining more favourable AOAs, and lift and drag distributions

Comparison of the computational fluid dynamics predictions of vertical axis wind turbine performance against detailed pressure measurements

Computational Fluid Dynamics (CFD) simulations are currently one of the most popular methods for the modelling of a Vertical Axis Wind Turbine (VAWT) that gives good insight on the turbine aerodynamics. The current study provides an assessment of the quality of the 2D and 3D CFD predictions of two highly recommended models in the literature, namely the SST K-ω model and the SST K-ω with the γ Intermittency transition model. The novelty of the study is in the kind of data that is used in the assessment. The CFD predictions of the pressure around the blade at several azimuthal angles are compared to the published experimental data measured by a high-frequency multiport pressure scanner. In addition, the predictions of the pressure contribution to the instantaneous power coefficient are compared to the experimental data. This paper sheds much new light on how the behaviour of the predictions of the SST K-ω with the γ intermittency transition model changes between the 2D and 3D cases and how the trends of the 2D results based on this transition model deviate from the detailed experimental data. This behaviour has not been previously investigated

Winglet design for vertical axis wind turbines based on a design of experiment and CFD approach

Vertical axis wind turbines (VAWTs) have been attracting an increasing attention in recent years because of their potential for effectively using wind energy. The tip vortices from the VAWT blades have a negative impact on the power efficiency. Since a winglet has been proved to be effective in decreasing the tip vortex in the aerospace field, this paper numerically studies the aerodynamic effect of appending a winglet on the blade of a VAWT. Based on the theoretical motion pattern of the VAWT blade, this paper simplifies the three-dimensional full-scale rotor simulation to a one-blade oscillating problem in order to reduce the computational cost. The full rotor model simulation is also used in validating the result. The numerical approach has been validated by the experimental data that is available in the open literature. Six parameters are applied in defining the configuration of the winglet. The orthogonal experimental design (OED) approach is adopted in this paper to determine the significance of the design parameters that affect the rotor’s power coefficient. The OED results show that the twist angle of the winglet is the most significant factor that affects the winglet’s performance. A range analysis of the OED results produces an optimal variable arrangement in the current scope, and the winglet’s performance in this variable arrangement is compared with the blade without a winglet. For the single blade study, the comparison result shows that the optimal winglet can decrease the tip vortices and improve the blade’s power performance by up to 31% at a tip speed ratio of 2.29. However, for the full VAWT case, the relative enhancement in the power coefficient is about 10.5, 6.7, and 10.0% for TSRs of 1.85, 2.29, and 2.52, respectively. The winglet assists in maintain the pressure difference between the two sides of the blade, thus weakening the tip vortex and improving the aerodynamic efficiency of the surface near the blade tip

Gonadal infection: a risk factor for the development of adolescent varicocele

Objective: The aim of this study was to determine whether a relationship between previous gonadal infections and adolescent varicocele occurrence exists.Patients and methods: All adolescents who presented with varicocele at Tanta Urology Department during the period from January 2006 to March 2011 were included in this study. Patients were evaluated for age, clinical presentation, previous history of epididymitis or epididymoorchitis, laterality, and grading of varicocele. Examination of testicular consistency and ultrasound measurement of testicular volume were carried out for all patients to define those with testicular atrophy.Results: Sixty-three boys were included in this study. The mean patients’ age was 15.6 years (range: 10–18, SD; 1.6 years). Twenty-nine (44.4%) boys had signs of testicular atrophy (testes are soft in consistency with ultrasounddetected volume smaller than that normal for age) either unilateral or bilateral. About 28.6% of patients (18 boys) had a history of epididymitis or epididymo-orchitis either associated with mumps or of unknown etiology. Of those patients, six boys had previous history of single attack, 10 boys had two attacks, and two boys had more than two attacks of epididymo-orchitis. A significant positive correlation was seen between the incidence of epididymo-orchitis attacks and the grade of varicocele (rs=0.63, 95% confidence interval: 0.21–0.85, P<0.05). Patients with past history of epididymo-orchitis were significantly more liable (4.1 times) of developing testicular atrophy as compared with those without a history of epididymo-orchitis (95% confidence interval: 1.517–11.097, P<0.05).Conclusion: History of epididymo-orchitis is significantly a potential risk factor for the development of adolescent varicocele with subsequently higher risk for testicular atrophy. We advise routine ultrasonographic examinations in patients with previous history of epididymo-orchitis both for possible early detection of varicocele and to avoid testicular atrophy in this cohort of patients. However, more studies on a larger scale are still warranted.Keywords: adolescent varicocele, epididymo-orchitis, testicular atroph

Techno-economic assessment of vertical axis wind turbine driven RO desalination with compressed air energy storage for remote communities

Renewable energy desalination is gaining much attention in remote off-grid communities facing challenges in accessing clean water. Typically, batteries ensure the continuous operation of small-scale renewable reverse osmosis (RO) desalination systems; however, they are expensive and have relatively shorter lifespans. This study investigates the implementation of a compressed air energy storage (CAES) system coupled with a vertical axis wind turbine (VAWT) to directly drive small-scale RO desalination, potentially replacing batteries and reducing energy conversions. A Simulink model was developed to simulate the performance of a VAWT-driven CAES operating RO units, adaptable for both technical and economic assessments. Parametric studies have identified the optimal configuration. The most cost-effective configuration, utilising eleven VAWTs and a pressure exchanger (PX), achieves a levelised cost of water (LCOW) of 1.63 US$/m3 and an annual water production of 9400 m3. The normalised daily water production per square metre of turbine swept area at the study site is 0.19 m3/m2/day at an average wind speed of 5 m/s. While this configuration has a higher initial capital cost, it yields the lowest LCOW. The CAES system effectively addresses the intermittency challenges of wind energy. This study presents a novel, battery-free VAWT-CAES-RO system as a sustainable desalination solution for remote communities, offering a promising approach to address water scarcity in an environmentally friendly manner

Response surface optimisation of vertical axis wind turbine at low wind speeds

The Vertical Axis Wind Turbines (VAWTs) have an increasing global market and this emphasis the need for to improve the performance of VAWTs, especially at relatively low wind speed. This paper utilises the Response Surface methodology to optimise the performance of a VAWT. A three bladed VAWT configuration was considered with a NACA0015 profile. Three significant input parameters were selected including the tip speed ratio, the turbine solidity, and the pitch angle. An extended range of each input parameter was chosen in order to gain a good insight into how these input parameters affect the performance of the VAWT. The high-fidelity Computational Fluid Dynamics (CFD) simulations were carried out for the modelling of the turbine. The use of the Response Surface Optimisation based on Multi-Objective Genetic Algorithm (MOGA) along with the CFD simulations is found to be useful in the selection of the optimal design of VAWT. Moreover, the 3D aspects of the VAWT geometry are investigated and these include the turbine aspect ratio and the effect of the blade tip geometry. The implementation of an optimised winglet at the tip of the turbine blades is found to provide a significant enhancement of the cycle averaged power coefficient, especially at low aspect ratios

COVID-19 Stroke Apical Lung Examination Study 2: a national prospective CTA biomarker study of the lung apices, in patients presenting with suspected acute stroke (COVID SALES 2)

BACKGROUND: Apical ground-glass opacification (GGO) identified on CT angiography (CTA) performed for suspected acute stroke was developed in 2020 as a coronavirus-disease-2019 (COVID-19) diagnostic and prognostic biomarker in a retrospective study during the first wave of COVID-19. OBJECTIVE: To prospectively validate whether GGO on CTA performed for suspected acute stroke is a reliable COVID-19 diagnostic and prognostic biomarker and whether it is reliable for COVID-19 vaccinated patients. METHODS: In this prospective, pragmatic, national, multi-center validation study performed at 13 sites, we captured study data consecutively in patients undergoing CTA for suspected acute stroke from January-March 2021. Demographic and clinical features associated with stroke and COVID-19 were incorporated. The primary outcome was the likelihood of reverse-transcriptase-polymerase-chain-reaction swab-test-confirmed COVID-19 using the GGO biomarker. Secondary outcomes investigated were functional status at discharge and survival analyses at 30 and 90 days. Univariate and multivariable statistical analyses were employed. RESULTS: CTAs from 1,111 patients were analyzed, with apical GGO identified in 8.5 % during a period of high COVID-19 prevalence. GGO showed good inter-rater reliability (Fleiss κ = 0.77); and high COVID-19 specificity (93.7 %, 91.8-95.2) and negative predictive value (NPV; 97.8 %, 96.5-98.6). In subgroup analysis of vaccinated patients, GGO remained a good diagnostic biomarker (specificity 93.1 %, 89.8-95.5; NPV 99.7 %, 98.3-100.0). Patients with COVID-19 were more likely to have higher stroke score (NIHSS (mean +/- SD) 6.9 +/- 6.9, COVID-19 negative, 9.7 +/- 9.0, COVID-19 positive; p = 0.01), carotid occlusions (6.2 % negative, 14.9 % positive; p = 0.02), and larger infarcts on presentation CT (ASPECTS 9.4 +/- 1.5, COVID-19 negative, 8.6 +/- 2.4, COVID-19 positive; p = 0.00). After multivariable logistic regression, GGO (odds ratio 15.7, 6.2-40.1), myalgia (8.9, 2.1-38.2) and higher core body temperature (1.9, 1.1-3.2) were independent COVID-19 predictors. GGO was associated with worse functional outcome on discharge and worse survival after univariate analysis. However, after adjustment for factors including stroke severity, GGO was not independently predictive of functional outcome or mortality. CONCLUSION: Apical GGO on CTA performed for patients with suspected acute stroke is a reliable diagnostic biomarker for COVID-19, which in combination with clinical features may be useful in COVID-19 triage