This paper explores the use of sharkskin in improving the aerodynamic performance of aerofoils. A biomimetic analysis of the sharkskin denticles was conducted and the denticles were incorporated on the surface of a 2-Dimensional (2D) NACA0012 aerofoil. The aerodynamic performance including the drag reduction rate, lift enhancement rate, and Lift to Drag (L/D) enhancement rate for sharkskin denticles were calculated at different locations along the chord line of the aerofoil and at different Angles of Attack (AOAs) through Computational Fluid Dynamics (CFD). Two different denticle orientations were tested. Conditional results indicate that the denticle reduces drag by 4.3% and attains an L/D enhancement ratio of 3.6%.
Boundary layers are affected by a number of different factors. Transition of the boundary layer is very sensitive to changes in geometry, velocity and turbulence levels. An understanding of the flow characteristics over a flat plate subjected to changes in geometry, velocity and turbulence is essential to try and understand boundary layer transition. Experiments were conducted in Low Turbulence wind tunnel (LTWT) at Northwestern Polytechnical University (NWPU), China to understand the effects due to changes in geometric profiles on boundary layer transition. The leading edge of the flat plate was changed and several different configurations ranging from Aspect Ratio (AR) 1 to 12 were used. Turbulence level was kept constant at 0.02% and the velocity was kept at default value of 30 m/s. The results indicated that as the AR increases, boundary layer thickness reduces at the same location along the plate. The displacement thickness shows that the fluctuations increase with an increase with AR which denotes the effect of leading edge on turbulence spot’s production. For AR≥4, an increase in AR led to an elongation of the transition zone and a delay in transition onset. Nomenclature
The emergence of the novel coronavirus has led to a global pandemic which has led to the airline industry facing severe losses. For air travel to recover, airlines need to ensure safe air travel. In this paper, the authors have modeled droplet dispersion after a single breath from an index patient. Computational Fluid Dynamics (CFD) simulations are conducted using the k-ωSST turbulence model in ANSYS Fluent. The authors have taken into consideration several parameters such as the size of the mouth opening, the velocity of the cabin air as well as the number of droplets being exhaled by the index patient to ensure a realistic simulation. Preliminary results indicate that after a duration of 20 s, droplets from the index patient disperse within a 10 m 2 cabin area. About 75% of the droplets are found disperse for up to 2 m axially behind the index patient. This could possess an enhanced risk to passengers sitting behind the index patient. Ultimately, this paper provides an insight into the potential of CFD to visualise droplet dispersal and give impetus to ensure that necessary mitigating measures can be taken to reduce the risk of infection through droplet dispersal.
This paper explores the use of Two-Dimensional sinusoidal surface features to delay transition and/or reduce drag. The authors, in this paper demonstrated that the presence of low amplitude sinusoidal surface features might damp the disturbances in the laminar boundary layer, reduce wall shear stress and maintain laminar flow for longer than a conventional flat plate. The hypothesis of the paper is inspired by the simplification of the dermal denticle on the surface of the shark-skin. Simulations are carried out using the Transition SST model in FLUENT based on the evidences of the transition model being suitable for a wider variety of high curvature scenarios. The surface waves are simulated for different amplitudes and wavelengths and their impact on transition onset and drag reduction are quantified at different velocities. Results presented in this paper indicate that a transition delay of 10.8% and a drag reduction of 5.2% are achievable. Furthermore, this paper adds credence to the notion that biomimicry is a very promising avenue for future drag reducing methods.
This paper describes numerical simulation of the effect of turbine exhaust flows on typical exhaust diffuser geometries. The study has been carried out on three different diffuser geometries. These diffusers have varying degrees of diffusion in the annular section. The studies were carried out at a Reynolds number of 7.7 × 105 based on the diffuser inlet hydraulic diameter. The performance of the diffusers was assessed in terms of total pressure loss and static pressure coefficient across the diffuser. The turbine exhaust flow was simulated by combining an injection scheme from the casing in to the main flow that changes the uniform diffuser inlet velocity profile to that of a typical turbine exhaust flow profile. It was observed that the presence of a realistic exhaust flow influences the diffuser performance compared to an axial inlet flow. The effect of the real flow seems to be to make it more resistant to adverse pressure gradients. The exit flow of the diffusers, studied earlier, with uniform axial inlet flow, showed massively separated regions at the diffuser delivery. The diffuser performances improved significantly with realistic simulation of turbine exhaust flow. The present study also reinforces the fact that the diffuser performance is highly sensitive to the quality of the inlet flow.
Aircraft wings and wind turbine blades are often subjected to harsh and cold climatic conditions. Icing is often observed on wing and blade surfaces in these cold climatic conditions. Wind turbine blades, in particular, are severely impacted by ice accretion which greatly hampers their performance and energy generation efficiency. Ice-accretion patterns are observed to vary with changes in temperature. As the temperature changes, the thickness of the ice accretion, the shape and location of ice-accretion vary greatly. In this paper, three different ice accretion patterns and their impact on the aerofoil efficiency have been investigated using the SST k – ω model in ANSYS CFD. An analysis of the impact of ice-accretion through a comparison of lift and drag coefficients for all three ice accretion patterns indicate that the accretion of ice on an aerofoil can reduce lift generation by 75.3% and increase drag by 280% thereby severely impacting the performance of the aerofoil. The loss in aerodynamic performance is greatly dependent on the ridge height, the extent of ice accretion and the thickness of this ice. The loss in aerodynamic performance has no fixed correlation to the drop in temperature.
This paper investigated the influence of limiter functions widely utilized in MUSCL-type (Monotone Upstream-centred Schemes for Conservation Laws) upwind numerical schemes on the solution accuracy of shockwave-containing flows. An incident shock interacting with laminar boundary layer developed on a flat plate was numerically simulated with the in-house developed code. A mixed-order grid convergence study was performed to assess the spatial errors of different limiters in simulating the selected shockwave-containing flow on flat plate. The conclusions are that, limiter functions implemented in the current in-house code play the critical roles in accurately predicting shockwave-containing flows. The mixed-order error estimator based on grid convergence study was proved to be applicable to evaluate the spatial errors of shockwave-containing flows, where the shock could reduce the nominal second- or third-order accuracy to first-order. The mixed-order estimator is conservative in the sense that the actual error is less than the error estimated, in the examined case.
Automation of aircraft instrument displays enhances flight safety, but it also increases complexity and pilot workload. Executing changes in flight plan, navigation or communication during flight using flight instrument switches often increases pilots' workload and this may also cause distraction that adds potential risks to flight safety. This study compares the conventional avionics panel and touchscreen avionic panel to find out the least distractive panel for the pilots. Thirty simulated flights using four different pilots were carried out; and aircraft speed, altitude and heading parameters using both avionics systems were observed to study the operational efficiency and pilot distraction resulted from each of the avionic systems. The distraction was examined by a parameter analysis based on the Mean Squared Error (MSE) mathematical model and visually by recording videos of each simulated flight. The results indicate that the touchscreen system is more efficient and less erroneous for the aircraft in maintaining the parameters as compared with the conventional system. There is also a clear relationship between task completion time and disruption level on the parameters control.
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