Numerical Study of Vortex Shedding behind a NACA 0009 Hydrofoil

This paper addresses the propeller singing mitigation strategy of implementing an anti-singing edge so that the vortex shedding mechanism causing the excitation at the trailing edge of the propeller blade can be reduced. A Reynolds-Averaged Navier Stokes model with a k-ε turbulence formulation in 2D-flow was used to investigate the problem numerically. Simulations on a NACA 0009 hydrofoil with varying inflow velocity, angle of attack, and bevel angle were done. The content in this paper is a summary of the work done by the author during his MSc Individual Project at University College London (Johannessen, MSc thesis, 2020).

A Semi-Empirical Approach to Gas Flow Velocity Measurement by Means of the Thermal Time-of-Flight Method

This paper presents a method of measuring gas flow velocity based on the thermal time-of-flight method. The essence of the solution is an analysis of the time shift and the shape of voltage signals at the transmitter and at a temperature wave detector. The measurements used a probe composed of a wave transmitter and a detector, both in the form of thin tungsten wires. A rectangular signal was used at the wave transmitter. The time-of-flight of the wave was determined on the basis of the time shift of two selected characteristic points of the voltage waveform at the transmitter and the wave detector. To obtain the correct velocity indication, a correction in the form of a simple power function was applied. From the measurements performed, the relative uncertainty of the method was obtained, from approx. 4% of the measured value at an inflow velocity of 6.5 cm/s to 1% for an inflow velocity of 50 cm/s and higher.

A Study on Diffuser Augmentation of a Tidal Turbine

As tidal energy is progressively earning attention worldwide, there is a lot of existing research about the tidal current potency and the tidal turbine design. Especially on turbine design, existing studies deduced that a diffuser augmentation is a superior choice to increase the turbine performance. However, the research in finding the best diffuser angle whose efficiency is maximum, yet minim cavity risk is still limited. Therefore, this study proposes an innovative, optimized design method on diffuser augmentation of a tidal turbine by comparing four diffuser angles in three inflow velocity circumstances. In particular, three airfoil blades design with a rotor diameter of 0.3 m was developed. The combination of computational fluid dynamic and multi-objective optimization using a general algorithm coupled with the artificial neural network was applied by considering the turbine’s power coefficient and cavitation inception as a trade-off objective. The numerical results display that the different inflow velocity affects the turbine performance insignificantly. The optimization analysis and comparison among four diffuser angles in three variations of inflow velocity show that the tidal turbine's optimal design with diffuser augmentation could be applied to all tidal current speed.

Effects of uniform vertical inflow perturbations on the performance of flapping wings

Flapping wings have attracted significant interest for use in miniature unmanned flying vehicles. Although numerous studies have investigated the performance of flapping wings under quiescent conditions, effects of freestream disturbances on their performance remain under-explored. In this study, we experimentally investigated the effects of uniform vertical inflows on flapping wings using a Reynolds-scaled apparatus operating in water at Reynolds number ≈ 3600. The overall lift and drag produced by a flapping wing were measured by varying the magnitude of inflow perturbation from J Vert = −1 (downward inflow) to J Vert = 1 (upward inflow), where J Vert is the ratio of the inflow velocity to the wing's velocity. The interaction between flapping wing and downward-oriented inflows resulted in a steady linear reduction in mean lift and drag coefficients, C ¯ L and C ¯ D , with increasing inflow magnitude. While a steady linear increase in C ¯ L and C ¯ D was noted for upward-oriented inflows between 0 < J Vert < 0.3 and J Vert > 0.7, a significant unsteady wing–wake interaction occurred when 0.3 ≤ J Vert < 0.7, which caused large variations in instantaneous forces over the wing and led to a reduction in mean performance. These findings highlight asymmetrical effects of vertically oriented perturbations on the performance of flapping wings and pave the way for development of suitable control strategies.

Efficacy and Safety of Qishen Yiqi Dripping Pill for Heart Failure With Preserved Ejection Fraction: A Systematic Review and Meta-Analysis

Background: The number of heart failure with preserved ejection fraction (HFpEF) patients is increasing year by year, yet all western medicines currently used for heart failure have been shown to be ineffective for HFpEF. Qishen Yiqi Dripping Pill is one of the commonly drugs for the treatment of heart failure in China. In recent years, some clinical studies found that it has curative effect on HFpEF.Objective: To evaluate the efficacy and safety of Qishen Yiqi Dripping Pill in treatment of HFpEF.Methods: Databases including CNKI, Wanfang, VIP, CBM, PubMed, Web of Science, The Cochrane Library and EMbase were searched from their inception to May 2020 to screen relevant randomized controlled trials. The “risk of bias” evaluation tool in the Cochrane Handbook was used to evaluate the quality of the included studies. RevMan 5.3 software was used for meta-analysis.Results: Eight studies meeting the criteria were included, with a total of 895 patients. The results of meta-analysis showed that compared with western medicine alone, combination of western medicine and Qishen Yiqi Dripping Pill can further increase the quotient of early diastolic mitral inflow velocity and late diastolic mitral inflow velocity (E/A) in patients with HFpEF [mean difference (MD) = 0.20, 95% CI (0.14, 0.26), p &lt; 0.000 01], decrease the quotient of early diastolic mitral inflow velocity and mitral annular tissue velocity (E/e′) [MD = −2.50, 95% CI (−3.18, −1.82), p &lt; 0.000 01], decrease brain natriuretic peptide (BNP) [MD = −151.83, 95% CI (−245.78, −57.89), p = 0.002], increase cardiac function improvement rate [relative risk (RR) = 1.30, 95% CI (1.11, 1.52), p = 0.001], and increase six-minutes walking distance (6-MWD) [MD = 64.75, 95% CI (22.65, 106.85), p = 0.003]. Four studies reported the occurrence of adverse reactions, among which three studies reported no adverse reactions and one study reported three patients with mild adverse reactions in the intervention group.Conclusion: Current evidence suggests that Qishen Yiqi Dripping Pill may be effective in the treatment of HFpEF. However, due to the low quality of the included studies, lack of placebo control, large heterogeneity among different studies, and great possibility of publication bias, the results of our review should be evaluated with more prudence, more high-quality clinical studies are needed to verify the conclusion in the future. In addition, the safety of Qishen Yiqi Dripping Pill remains uncertain, further assessment is required in the future.

Effects of Mean Inflow Velocity and Droplet Diameter on the Propagation of Turbulent V-Shaped Flames in Droplet-Laden Mixtures

Three-dimensional carrier phase Direct Numerical Simulations of V-shaped n-heptane spray flames have been performed for different initially mono-sized droplet diameters to investigate the influence of mean flow velocity on the burning rate and flame structure at different axial locations from the flame holder. The fuel is supplied as liquid droplets through the inlet and an overall (i.e., liquid + gaseous) equivalence ratio of unity is retained in the unburned gas. Additionally, turbulent premixed stoichiometric V-shaped n-heptane flames under the same turbulent flow conditions have been simulated to distinguish the differences in combustion behaviour of the pure gaseous phase premixed combustion in comparison to the corresponding behaviour in the presence of liquid n-heptane droplets. It has been found that reacting gaseous mixture burns predominantly under fuel-lean mode and the availability of having fuel-lean mixture increases with increasing mean flow velocity. The extent of flame wrinkling for droplet cases has been found to be greater than the corresponding gaseous premixed flames due to flame-droplet-interaction, which is manifested by dimples on the flame surface, and this trend strengthens with increasing droplet diameter. As the residence time of the droplets within the flame decreases with increasing mean inflow velocity, the droplets can survive for larger axial distances before the completion of their evaporation for the cases with higher mean inflow velocity and this leads to greater extents of flame-droplet interaction and droplet-induced flame wrinkling. Mean inflow velocity, droplet diameter and the axial distance affect the flame brush thickness. The flame brush thickens with increasing droplet diameter for the cases with higher mean inflow velocity due to the predominance of fuel-lean gaseous mixture within the flame. However, an opposite behaviour has been observed for the cases with lower mean inflow velocity where the smaller extent of flame wrinkling due to smaller values of integral length scale to flame thickness ratio arising from higher likelihood of fuel-lean combustion for larger droplets dominates over the thickening of the flame front. It has been found that the major part of the heat release arises due to premixed mode of combustion for all cases but the contribution of non-premixed mode of combustion to the total heat release has been found to increase with increasing mean inflow velocity and droplet diameter. The increase in the mean inflow velocity yields an increase in the mean values of consumption and density-weighted displacement speed for the droplet cases but leads to a decrease in turbulent burning velocity. By contrast, an increase in droplet diameter gives rise to decreases in turbulent burning velocity, and the mean values of consumption and density-weighted displacement speeds. Detailed physical explanations have been provided to explain the observed mean inflow velocity and droplet diameter dependences of the flame propagation behaviour.