Single Rotor Research Articles

Assessment of advanced RANS turbulence models for prediction of complex flows in compressors

Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) has been widely used in compressor design and analysis. However, reasonable prediction of compressor flow and its impact on compressor performance remains challenging. In this study, Menter’s Shear Stress Transport (SST) model and its variants, as well as the ω-based Reynolds stress model (Stress-BSL) are assessed. For a single rotor (Rotor 67), under the peak efficiency operating condition, all studied turbulence models predict its performance with reasonable accuracy; under the off-design conditions, SST with Helicity correction (SST-Helicity) shows superiority in predicting the effect of flow on the spanwise distribution of aerodynamic parameters. For Darmstadt’s 1.5-stage transonic axial compressor, SST-Helicity outperforms SST, SST with the Quadratic Constitutive Relation (SST-QCR) and Stress-BSL in predicting the performance as well as the spanwise distribution of aerodynamic parameters. At the design rotating speed, the stall margin given by SST-Helicity (20.90%) is the closest to the experimental measurement (24.81%), which is more than twice that by SST (8.71%) and 1.5 times that by SST-QCR (14.14%). This paper demonstrates that SST-Helicity model, together with a good quality and sufficiently refined grid, can capture the compressor flow features with reasonable accuracy, which results in a credible prediction of compressor performance and stage matching.

Modelling, control and simulation of a single rotor UAV with swashplateless torque modulation

Single rotor-base unmanned aerial vehicles (UAVs) represent the most minimalistic design to implement an aerial vehicle. We describe here a mono-rotor UAV, also named mono-spinner, that uses torque modulation (also called swashplateless mechanism) to provide roll and pitch control without the need of a complicated swashplate mechanism. A full non-linear model of the mono-spinner based on the Euler-Poincaré theoretical framework is given including a description of the structure of the drone and its rotor control system. Mechanical properties, kinetic energy and all of the external forces of interest to derive the equations of motion are described. A novel, Lyapunov-stable, quaternion-based nonlinear control law based on the decomposition of the orientation quaternion into a spin component and a reduced orientation component is provided. Finally, simulation results based on parameters measured from a real implementation of a mono-spinner are produced.

The novel left atrial anterior 'seatbelt' line reduces sustained atrial arrhythmia by 72% compared to pulmonary vein isolation alone in a cohort of 400 virtual atria models

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No.860974. Background The success-rate of pulmonary vein isolation (PVI) is modest in persistent atrial fibrillation (AF), but additional empirical ablation, such as posterior wall isolation (PWI), has not been shown to reduce the rate of AF recurrence. The "seatbelt", an anterior linear ablation lesion connecting the right superior pulmonary vein to the mitral annulus, is a novel substrate modification approach that is yet to be tested in a large-scale randomised clinical trial. Purpose To use in-silico trials with human-based modelling and simulation to compare the efficacy of (i) PVI alone, (ii) PVI and PWI (PVI+PWI), or (iii) PVI and seatbelt (PVI+SB) for the prevention of atrial arrhythmia in large populations of virtual patient models. Methods AF was simulated in a cohort of 400 virtual atrial models with anatomical and electrophysiological variability, with AF persisting for >7 seconds defined as sustained. Models which sustained AF were each independently subjected to all three ablation approaches before repeating the AF induction protocol. Results Three hundred forty-four (86%) atrial models developed sustained AF at baseline. After applying the ablation lesions, substantially fewer models sustained atrial arrhythmias in the PVI+SB group (50 [14%] vs. 134 [39%] with PVI+PWI vs. 172 [50%] with PVI). PVI+SB was more effective than PVI and PVI+PWI in preventing both AF and atrial flutter (i.e., presence of a single rotor), since PVI and PVI+PWI led to the formation of anatomical re-entries around the rings of the pulmonary veins and the posterior wall of the left atrium, respectively (Figure). Therefore, PVI+SB restricted atrial flutter mainly to the right atrium (either anatomical, around the inferior cava vein, or functional, meandering throughout the venous portion of the right atrium, Figure). Importantly, in all three ablation strategies, the likelihood of AF recurrence was directly proportional to the surface area of the right atrium (AF probability increased 0.95%/cm², 0.88%/cm² and 0.56%/cm² after PVI+SB, PVI+PWI and PVI, respectively). The role of the right atrial size was less accentuated for PVI alone, since after the ablation the entire left atrial body was still available for rotor anchoring. Moreover, an enlarged left atrium enabled the appearance of micro-re-entries in the anterior and inferior wall of the left atrium, even after applying floor and roof lines. One atrial model additionally presented a rotor in the posterior wall of the left atrium after completely isolating it from the left atrial body. Conclusion(s) In a cohort of 400 virtual atrial models, PVI+SB reduced sustained atrial arrhythmias by 72% compared to PVI alone and by 64% to PVI+PWI, but AF could still originate in an enlarged right atrium.

Phase-Resolved Flowfield Measurements of a Coaxial Counter-Rotating Rotor in Hover

The flowfield of a coaxial counter-rotating rotor in hover was measured using particle image velocimetry. The goal of the measurements was to investigate the flow features of coaxial rotors, including interaction between the rotors, and to measure inflow over the rotor radius and azimuth. The phase-resolved measurements were performed at several azimuthal index angles behind the rotor blades, with 500 instantaneous flow realizations per azimuth. Axial velocity profiles extracted from the phase-averaged flowfields exhibited the effect of bound circulation associated with blade passage, the trailed vortex sheet, and the effect of the blade tip vortex. Tip vortex characteristics were extracted from the measurements and were shown to compare well with semi-empirical models in most cases. The measured inflow was captured well by blade element momentum theory when the mutually induced velocities were accounted for. The lower rotor was found to behave more like an isolated single rotor, whereas tip vortices from the upper rotor convected faster radially inward and downstream than the lower rotor tip vortices. Upper and lower rotor tip vortices exhibited similar core radii ranging from 12 to 18% of the rotor blade chord, and they grew at a similar rate. However, this vortex growth rate was different from that of an isolated single rotor.

Experiments on upstream induction and wake flow for multirotor wind turbines

Multirotor wind turbine concepts are increasingly discussed as cost-effective alternatives for floating wind energy installations. When multiple smaller rotors are installed next to each other, the individual rotors experience local blockage from their neighbours. Depending on the rotor arrangement, the flow through and around the multirotors will differ leading to a local variation in axial forcing and power output on the individual rotors. In this lab-scale experiment, we investigate how the spacing between the single rotors in a multirotor of seven actuator discs affects the upstream flow, thrust force distribution and downstream wake flow. Reducing the inter-rotor spacing is observed to cause larger zones of upstream velocity reductions, both in streamwise and lateral direction. Consequently, the difference in thrust force between a locally blocked central rotor and the surrounding rotors also increases for smaller rotor spacing. Measurements of the downstream wake flow behind a multirotor model indicate a lower initial velocity deficit compared to a single rotor. Reduced rotor spacing is found to increase the wake’s initial velocity deficit and turbulence levels. Consequently, the wake recovers faster, resulting in similar velocity deficits independent of the rotor-spacing in the far wake region.

Sensorless Control Based on the Uncertainty and Disturbance Estimator for IPMSMs With Periodic Loads

The research object in this paper is a single rotor compressor based on the interior permanent magnet synchronous motors (IPMSM) with sensorless control, whose load fluctuates periodically with the mechanical angle. The periodically fluctuating loads can cause obvious periodic fluctuations of motor speed. Meanwhile, the traditional phase-locked loop (PLL) can lead to obvious phase shift and amplitude attenuation. Therefore, the controller is designed from two aspects to make the motor run stably at low speed under the periodic load. Firstly, a speed control based on the uncertainty and disturbance estimator (UDE) is proposed to suppress speed fluctuations caused by the periodic load. Secondly, the phase-locked loop based on the resonance control (R-PLL) is proposed to compensate for the periodic angle and speed errors caused by the phase shift coming from the PLL under the periodic load. The experimental results show that the sensorless control based on the R-PLL and UDE can effectively improve the estimated angle accuracy and suppress the speed fluctuations, making the motor run stably at low speed under periodic loads.

A RANS-based surrogate model for simulating wind turbine interaction

A new wake surrogate model based on Reynolds-averaged Navier-Stokes (RANS) single rotor simulations is presented. The model relies on a series of three-dimensional pre-calculated deficit and added turbulence intensity flow fields, stored in a look-up table (LUT) as a function of the thrust coefficient and the ambient turbulence intensity. For any combination of these parameters, the flow around a wind turbine can be predicted by linearly interpolating within the look-up table. Furthermore, the resulting three-dimensional flow fields from different turbine sources can be superposed linearly to calculate the total wind farm flow. The model is implemented in PyWake and benchmarked against other, commonly employed engineering wake models, namely the Gaussian-Bastankhah, the N. O. Jensen and the Zong models, where RANS wind farm simulations are used as reference. In both full and partial wake cases, the surrogate model achieves a higher accuracy than any other model. Besides providing an accuracy comparable to a full RANS solution, the model can compute a flow case in the order of 1 s on a single processor. The main disadvantage is that the generation of the look-up table is time consuming, computationally expensive and can be memory demanding (especially if more inputs, such as the yaw misalignment angle, stability, etc. are added). Nevertheless, generating the LUT only has to be done once per wind turbine type.

Experimental Study on the Effect of the Blade Tip Distance on the Power and the Wake Recovery with Small Multi-Rotor Wind Turbines

In order to investigate the output power and wake velocity of small multi-rotor wind turbines compared to single-rotor wind turbines, which operate in the same swept area at various blade tip distances, this paper used the wind tunnel test method to examine single-rotor wind turbines with diameter D of 0.4 m and 0.34 m corresponding to the triple-rotor wind turbines and double-rotor wind turbines with a single rotor diameter D of 0.24 m, respectively. The experimental results indicated that, without rotation speed control, the triple-rotor wind turbine produced more power than the single-rotor wind turbine with an equivalent swept area and that the output power tended to rise initially and then fall as the distance between each rotor increased. Moreover, the power increase reached a maximum of 8.4% at the 0.4D blade tip distance. In terms of wake measurement, triple-rotor wind turbines had smaller wake losses and faster recovery rates than single-rotor wind turbines. The smaller the blade tip distance, the earlier the wake merged and fused and the faster the recovery rate. In designing small multi-rotor wind turbines, the above discussion can serve as a guide.

Acceleration of indirect detection 195Pt solid-state NMR experiments by sideband selective excitation or alternative indirect sampling schemes

The measurement of the of chemical shift (CS) tensors via solid-state NMR (ssNMR) spectroscopy has proven to be a powerful probe of structure for organic molecules, biomolecules, and inorganic materials. However, when measuring the NMR spectra of heavy spin-1/2 isotopes the chemical shift anisotropy (CSA) is commonly on the order of thousands of parts per million, which makes acquisition of NMR spectra difficult due to the low NMR sensitivity imposed by the breadth of the signals and challenges in uniformly exciting the NMR spectrum. We have recently shown that complete 195Pt NMR spectra could be rapidly measured by using 195Pt saturation or excitation selective long pulses (SLP) with multiple rotor-cycle durations and RF fields less than 50 kHz into 1H{195Pt} or 1H-31P{195Pt} PE S-RESPDOR, TONE D-HMQC-4, J-resolved, and J-HMQC pulse sequences. The SLP only provide signal or dephasing when they are applied on resonance with a spinning sideband. The magic angle spinning 195Pt NMR spectrum is reconstructed in the sideband selective NMR experiments by acquiring 1D NMR spectra at variable 195Pt pulse offsets. In this work, we present a detailed investigation of the specific pulse conditions required for the ideal performance of sideband selective experiments. Sideband selective experiments are shown to be able to accurately reproduce MAS NMR spectra with minimal distortions of relative sideband intensities. It is also demonstrated that a 195Pt NMR spectrum indirectly detected with HMQC can be rapidly obtained by acquiring a single rotor cycle of indirect dimension evolution points. We dub this method One Rotor Cycle of Acquisition (ORCA) HMQC. Sideband selective experiments and ORCA HMQC experiments are shown to provide a one order of magnitude improvement in experiment times as compared to conventional wideline HMQC experiments.

Numerical simulation of the flow field and radiation noise from a pump-jet propulsor under various stator pre-whirl angles

The effects of different stator pre-whirl angles on the hydrodynamic and noise performance of a pump-jet propulsor (PJP) are studied; these angles are the inlet, outlet, and stagger angles. The stress-blended eddy simulation (SBES) approach, used to describe flow details around a PJP, is combined with the variational Lighthill's analogy to perform the acoustic calculation. The discrete peaks of the unsteady thrust of a single rotor blade and of all of the rotor blades are located at the harmonics of the blade passage frequency for stator (BPFs) and the blade passage frequency for rotor (BPFr), respectively. The trend in the amplitude with the pre-whirl angle at various harmonics follows no systematic rule, but the excessive pre-whirl angle increases the amplitude in the whole spectrum. With increases in pre-whirl angle, the stator sheet vortex and root vortex are weakened and enhanced, respectively, leading to a reduction of the high turbulent kinetic energy (Tk) regime at the root. Further study of the PJP sound indicates that the discrete tonal noise is located at the BPFs, BPFr, and their harmonics; the pre-whirl angle does not affect these locations, except in the largest inlet angle case. The cases with the least pre-whirl angle have an extremely low noise level, particularly at the outlet angle, which has an obvious downstream directivity.

Numerical investigation of the aerodynamic and wake characteristics of a floating twin-rotor wind turbine under surge motion

To elevate the power capacity of floating wind turbines and cut costs, development towards large-scale systems is underway. However, this requires solving the problem of fatigue loading on large, flexible blades, as well as corresponding improvements to production and installation technology. As an alternative to larger turbines, twin-rotor floating wind turbines have been proposed. The aerodynamic and wake interference characteristics of this twin-rotor are not yet well understood. In this study, we have investigated the power and wake characteristics of a twin-rotor floating wind turbine based on unsteady Reynolds-averaged Navier-Stokes turbulence model for a comprehensive analysis. Specifically, the power and wake recovery of a twin-rotor floating horizontal-axis wind turbine (FHAWT) under surge motion are compared in detail with those of a single floating wind turbine and bottom-fixed case, while both the effects of the three wind directions (β = 0°, 45°, 90°) and spacing ratios (S/D = 1.2, 1.375, 1.5) are considered. The results suggest that the mean power of the twin-rotor is enhanced by a maximum of 13% under surge motion compared to the single rotor, the small spacing ratio promotes the power gain. Surge motion plays a significant role in wake interaction between the twin-rotor and facilitates wake recovery. As compared to the baseline case, both power and wake recovery performance of the twin-rotor are boosted at β = 45°, with an increase in power of 12.7% as opposed to the single rotor. The modified Jensen wake model is proposed for the far-wake region and a modified Gaussian wake model is also suggested for different cases. This study can provide affiliated guidance for the application of the twin-rotor floating wind turbine.

Whirl-flutter control through direct piezoelectric effect

The aeroelastic instability known as whirl-flutter must be considered during the design of a propeller-driven aircraft. Usually, aircraft with single or multiple rotors may suffer with such phenomenon, especially when large rotor diameter is applied, such as vertical take-off and landing aircrafts (VTOL) with or without tilt rotors. Depending on the cruise speed, the whirl-flutter influences the project of rotors, wings and pylons. With the advent of modern air mobility, a better understanding of such phenomenon, as well as the development of vibrational control techniques to increase the stability margins becomes important. Although smart materials, such as piezoceramics, are commonly applied to control aeroelastic phenomena, the application to whirl-flutter control remains uninvestigated. Thus, the present research proposes passive control technique based on the direct piezoelectric effect, in a unimorph and bimorph harvester configurations, observing its effect on the aeroelastic system’s behavior. As main result of the piezoelectric material presence, an increased the flutter speed is observed, improving the system’s stability. Additionally, the bimorph configuration is more efficient to postpone the critical speed.

An Inbuilt Electronic Pawl Gates Orbital Information Processing and Controls the Rotation of a Double Ratchet Rotary Motor.

A direct external input energy source (e.g., light, chemical reaction, redox potential, etc.) is compulsory to supply energy to rotary motors for accomplishing rotation around the axis. The stator leads the direction of rotation, and a sustainable rotation requires two mutual input energy supplies (e.g., light and heat, light and pH or metal ion, etc.); however, there are some exceptions (e.g., covalent single bond rotors and/or motors). On the contrary, our experiment suggested that double ratchet rotary motors (DRMs) can harvest power from available thermal noise, kT, for sustainable rotation around the axis. Under a scanning tunneling microscope, we have imaged live thermal noise movement as a dynamic orbital density and resolved the density diagram up to the second derivative. A second input energy can synchronize multiple rotors to afford a measurable output. Therefore, we hypothesized that rotation control in a DRM must be evolved from an orbital-level information transport channel between the two coupled rotors but was not limited to the second input energy. A DRM comprises a Brownian rotor and a power stroke rotor coupled to a -C≡C- stator, where the transport of information through coupled orbitals between the two rotors is termed the vibrational information flow chain (VIFC). We test this hypothesis by studying the DRM's density functional theory calculation and variable-temperature 1H nuclear magnetic resonance. Additionally, we introduced inbuilt pawl-like functional moieties into a DRM to create different electronic environments by changing proton intercalation interactions, which gated information processing through the VIFC. The results show the VIFC can critically impact the motor's noise harvesting, resulting in variable rotational motions in DRMs.

Influence of Casing Groove on Rotating Instabilities in a Low-Speed Axial Compressor

AbstractRotating instability (RI) can be regarded as a pre-stall signal because such phenomena are usually detected when a compressor operates at a near-stall point. Since RI is closely relevant to aerodynamic, acoustic, and structural issues, its mechanism has attracted industrial concerns and in-depth analysis. In this paper, a low-speed axial single compressor rotor row is selected as the baseline research object. A circumferential casing groove is mounted over the shroud. The solid casing and the casing treated configurations were simulated using the zonal large eddy simulation model, and the simulations present remarkable predictions in capturing the averaged and dynamic characteristics of the investigated compressor. By implementing a data-driven method called dynamic mode decomposition, the mode with the highest amplitude is proved to be correlated to the dominant RI frequency. The spatial and temporal property of the RI is visualized. The results show that the casing groove has limited influence on the averaged flow field but manipulates the dynamic features. The groove allows the RIs to shift from around 0.5 blade passing frequency to higher frequencies in the upstream region and effectively suppresses the unsteadiness in the zones under and downstream of the groove. The RIs are triggered by the flow interaction of the tip leakage flow at the front part of the blade. It can be depicted as pressure waves staggering with the rotor blade and propagating over the blade tip region at around half of the blade speed. With the existence of the casing groove, the dominant wavelength changes, and the fluctuation is damped under the groove, which finally modifies the properties of RIs.

Prediction of aerodynamic performance of NREL offshore 5‐MW baseline wind turbine considering power loss at varying wind speeds

AbstractIn this study, a computational fluid dynamics (CFD) model was developed to simulate the aerodynamic performance of the National Renewable Energy Laboratory (NREL) offshore 5‐MW baseline wind turbine with single rotor and full wind turbine. Using statistical methods, the relation between pitch angle and performance when the speed is above the rated wind speed was analyzed; furthermore, other published data were compiled to establish the functional equations of power, thrust with various inflow wind speeds, and pitch angles. In addition, according to shape optimization based on parametric modeling, the two‐dimensional cross‐section of the wind turbine blade can be defined through a metasurface approach, and the three‐dimensional surface modeling of the wind turbine blade, nacelle, and tower is completed using the nonuniform rational B‐splines (NURBS) interpolator. In terms of aerodynamic simulation, the unstructured polygon mesh was used herein to discretize the space and simulate the highly curved and twisted surfaces of the blade. In this study, the compact and accurate mesh form obtained through a grid independence test will be used to analyze the distribution of the pressure coefficient, shear stress coefficient, and limited streamline on the blade surface at various inflow wind speeds and pitch angles to understand the differences between different turbulence models and the causes of power and thrust attenuation at high inflow wind speeds. In addition, the phenomena of blade‐tip vortices, dynamic stall, blade loading, and the interaction between nacelle and tower were collectively explored.

Investigations on Integrated Funnel, Fan and Diffuser Augmented Unique Wind Turbine to Enhance the Wind Speed

Wind energy is an alternative future energy to fossil fuels since it is abundant and green energy. As a result, high performance unique design is proposed that has a diffuser augmented wind turbine including intake funnel with guide vanes, natural fan, straight flow section, exit splitter with air openings and end flange. This proposed design is called as Integrated omni-directional Intake funnel, Natural fan, Straight diffuser, Splitter and Flange (I2NS2F) Design. To construct this I2NS2F configuration, four distinct wind turbines were developed: a) bare wind turbine, b) wind turbine diffuser design with single rotor turbine, c) bend diffuser, intake funnel, natural fan, splitter and flange and d) I2NS2F design. The proposed designs are numerically studied using MATLAB Simulink and Ansys Fluent. These designs are optimized by Random Search Optimization with Supervisory Control and Data Acquisition technique to evaluate the wind velocity and the performance is comparatively estimated. From this analysis, I2NS2F design achieves 53m/s of wind velocity at turbine region for 5.5m/s inlet wind and it could be considered as highest wind velocity than other three designs. It is evidently proved and concluded that proposed I2NS2F design augments natural wind, resulting in greater green power generation.

Near wake hydrodynamics and structural design of a single foil cycloidal rotor in regular waves

We present a hydrodynamic and structural model to design a single foil wave cycloidal rotor in regular waves. The hydrodynamic part considers potential flow and represents the foil as a point vortex. Unsteady effects are accounted for through Theodorsen’s function. The structural part utilises beam theory to compute the bending moments and stresses on the foil of the cyclorotor. The validity of the hydrodynamic model is explored with the aid of CFD, and the CFD results are bench marked versus experimental measurements. Results show that the hydrodynamic model estimates the mean radial loading on the foil within 20%–25% in attached flow conditions, whilst it is accurate to predict the mean tangential loading only when operating close to stall, at maximum lift conditions. Because the optimal structural operation of the rotor is in attached flow conditions, and close to stall, we utilise the coupled model to design a rotor that operates optimally for a range of different sea conditions. We find that with careful dimensioning of the radius and span, power extraction in regular waves can be optimised, whilst the structural penalty is kept constant at the allowable stress level.

Simulation of Rotor-Rotor Interaction and Noise of an Axial Counter-Rotating Fan

The Counter-Rotating Fan (CRF) offers higher aerodynamic performance, in terms of pressure head and aerodynamic efficiency, compared to the single rotor fan, thus making it an attractive solution for equipment cooling and ventilation of mines and tunnels. Nevertheless, further investigations are required to understand the flow interactions between the front rotor (FR) and the rear rotor (RR), as these interactions are sources of noise emission. This numerical study used the Unsteady Reynolds Average Navier-Stokes (URANS) flow simulations and the Fast Fourier transformation (FFT) to analyse the rotor-rotor interactions and consequences on the aero-acoustic performance. The static pressure fluctuations were recorded at several locations and analysed by FFT to reveal the mechanisms of flow interactions and the effects of axial inter-distance between the two rotors. The inter-distance seems to influence the aerodynamic loading of RR more than that of FR and the total-to-static isentropic efficiency tends to drop. Over one chord distance, the noise level decreases but at the expense of isentropic efficiency. The balanced performance does not seem to improve for an inter-distance greater than 1.5 chords, considered the optimum distance in this study. Finally, a graphical correlation which can be used to estimate the Sound Pressure Level (SPL) is developed for this category of CRF.

A wind tunnel investigation of yawed wind turbine wake impacts on downwind wind turbine performances and wind loads

In the current work we experimentally explored yawed wind turbine wake impacts on downwind wind turbine performances and wind loads. The lab-scale wind turbine model with a rotor diameter ( D) of 0.442 m and a height of 1 m (=2.26 D) was installed in a closed-circuit boundary layer wind tunnel (test section: 15 m long × 3.6 m wide × 2.0 m high) of the Research Institute for Applied Mechanics (RIAM) of Kyushu University. Power performance tests were initially conducted with a single rotor in isolation in order to characterize a rotor’s power output in stand-alone conditions. A detailed comparison of the tests revealed that the power output decreased rapidly as the yaw angle (γ) increased. It is presumed that the power output decrease in yawed cases is mainly due to the decrease in the effective rotor area and the change in the angle of the incoming wind flow with respect to the wind turbine blade. Next, using two wind turbine models aligned with the dominant inflow direction, the merging wakes behaviors caused by three different lateral separation distances were tested: (a) Case 1 ( y = 0), (b) Case 2 ( y = 0.5 D), and (c) Case 3 ( y = 1 D). Here, the separation distance between the two wind turbine models was fixed at 6 D in all cases. Extremely large power output deficits of 46%–76% were seen in the Case 1 configuration. This is mainly due to the significant wake velocity deficits induced by the upwind wind turbine model. In the Case 2 configuration with γ values of 20° and 30°, a significant increase in the power output of the downwind wind turbines was observed. Similar to Case 1 configuration, these results are considered to be mainly due to the upwind turbine-induced wake velocity deficits and wake deflection. Finally, in the Case 3 configuration, no significant difference was found in all of the results, and the tendency was almost the same. We show that the wake velocity deficits induced by the upwind wind turbine model had almost no effect on the power output of the downwind wind turbine model. We evaluated the total power output of the two turbines. As a result, in the Case 2 configuration with 20° yaw angle, the total power output of the two wind turbine models was the highest due to the increase in the power output of the downwind wind turbine model. In order to investigate the main cause of the significant increase in the power output of the downwind wind turbine model at 20° and 30° yaw angles in the Case 2 configuration, we measured the lateral wind speed distribution at the 6 D position on the downwind side of the upwind wind turbine model by using the ultrasonic anemometer. As a results, it was clarified that the peak of the wake velocity deficits induced by the upwind wind turbine model is clearly shifted away from the downwind turbine such that it experiences a smaller deficit due to wake steering. Also, with wake steering the upwind turbine-induced wake velocity deficits may be smaller due to the reduction in rotor area. Finally, it is extremely important to understand the wind load acting on the downwind wind turbine model operating within the wake region induced by the upwind yawed wind turbine model when the maximum power output is generated. It can be seen that as the yaw angle of the upwind wind turbine model increased, the power output generated by the downwind wind turbine model and the streamwise wind load acting on it also increased. However, it was also clarified that the streamwise wind load acting on the downwind wind turbine model in this situation did not exceed the stand-alone value.

A Computational Investigation of the Hover Mechanism of an Innovated Disc-Shaped VTOL UAV

Inventive approaches are constantly being revealed in the field of vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV) configuration concepts and designs. To date, a body-associated configuration of UAVs for augmented lift remains unclear among other approached designs. The current paper investigates the mechanism of a high-lift ducted fan mounted in the central body for VTOL UAV designs. We report an unresolved design of a disc-shaped UAV with a single rotor that aims to enhance the cost-effectiveness of fuel consumption with a substantial contribution of body lift to hover thrust. The convex upper surface curvature was applied to generate a significant lift contribution from the body during hover. The computational fluid dynamics (CFD) approach based on unstructured discretization followed by three-dimensional steady Reynolds-averaged Navier–Stokes (RANS) flow was applied in ANSYS CFX to mechanistically investigate the underlying design considerations. The disc-shaped UAV uses the lip curvature on the duct inlet to generate a vertical force that demonstrates a significant contribution of 95% of the rotor thrust during hovering. The UAV’s upper surface generates prolonged flow entrainment free from momentum losses in swirling flows. This phenomenon is followed by reduced power consumption in hovering and vertical flight, making the UAV aerodynamically stable and environmentally safe.