Range Of Airspeeds Research Articles

Power Generation Enhancement of Horizontal Axis Wind Turbines Using Bioinspired Airfoils: A CFD Study

This research investigates the performance implications of employing a bioinspired airfoil (seagull’s wing cross-section) in horizontal-axis wind turbines. Specifically, we replaced the S809 airfoil from NREL Phase VI with an airfoil modeled after seagull wings. Initially, we calibrated four coefficients of the GEKO turbulence model for both the S809 and the bioinspired airfoil, utilizing experimental data. Subsequently, using the calibrated generalized k-ω (GEKO) model, we conducted a comparative analysis between the S809 and the seagull airfoils, revealing the considerable superiority of the seagull airfoil in terms of lift and drag coefficients. Furthermore, we numerically simulated the original NREL Phase VI turbine and a modified version where the S809 airfoil was replaced with the seagull airfoil using 3D computational fluid dynamics (CFD) with the airfoil-based-calibrated GEKO turbulence model. This investigation spanned a wide range of air speeds, including 7 m/s, 13 m/s, and 25 m/s. At these wind speeds, we observed a substantial increase in turbine power generation, with enhancements of 47.2%, 204.4%, and 103.9%, respectively. This study underscores the significant influence of nature’s designs in advancing energy extraction within industries, particularly within the wind energy sector.

An observation methodology for non-measurable rotorcraft states

In an attempt to reduce acoustic pollution due to terminal flight phases (lift-offs and landings) in the surroundings of heliport, project MANOEUVRES developed a device capable of estimating the acoustic footprint of helicopters on the ground. This device requires knowledge of certain quantities that cannot be directly measured through physical sensors: the tip-path plane angle of attack and the main rotor thrust coefficient. Previous research has demonstrated that these quantities can be accurately estimated using observers that are properly fed with directly measurable flight mechanics and rotor state variables. However, these observers, which are based on linear mathematical models identified offline and employed through interpolation with respect to nominal airspeed, have shown poor robustness when the number of identification input cases is reduced, as required for a realistic design of observers in the field. This issue has particularly emerged when non-trimmed manoeuvres were considered during observation testing. To address this issue, this paper introduces a new baseline for the observation model, which includes dynamic pressure as an additional input. Moreover, a different model structure is considered depending on the observed variable. Specifically, for the tip-path plane angle of attack, a single model covers the entire airspeed range, while observation models for the rotor thrust coefficient are interpolated based on flight altitude. This new approach demonstrates results of comparable or superior quality to previous observation models. Furthermore, it exhibits increased robustness when the pool of identification cases used for observer synthesis is significantly reduced. Such improved performance and ease of synthesis pave the way for the setup and adoption of the proposed observers in the field.

Experimental evaluation of the drag curves of small fixed wing UAVs

Abstract Tight budgets often limit the scope of test campaigns within the development programmes of small uncrewed air vehicles (UAVs). This paper explores a range of combinations of instrumentation suites and protocols for both wind tunnel and flight evaluation, focusing on the key aspect of drawing up the drag curve of the airframe. Through extensive testing of a 5kg maximum take-off mass, fixed wing, twin motor, richly instrumented test platform, we show that automated glides over a range of airspeeds and the slow down manoeuvre are effective ways of determining power-off drag, while estimating thrust from propeller speed, and voltage and current sensing based methods work well for the power-on case. We also seek the most time-efficient and robust mix of the above manoeuvres to yield a given drag curve accuracy level and we find wind condition impacts the manoeuvre makeup of the optimal strategy.

Numerical simulation study on the exhaust gas migration of fuel vehicles under an airflow field in the confined space of an underground coal mine

As the main tool for transporting people and materials in coal mines with inclined shafts, fuel vehicles easily cause exhaust gas accumulation and significant pollution due to the special underground environment. In this paper, the problem of exhaust gas migration under the action of a special airflow field in underground confined space is studied. First, a physical model of exhaust gas migration in the confined space of an underground coal mine is established. By combining numerical simulations with field measurements, the law of exhaust gas migration of fuel vehicles under the action of an airflow field in a confined space is studied. The results show that the migration and diffusion of CO gas in exhaust gas are affected by airflow, and the concentration decreases with an increasing distance. The main irregular pollution area is concentrated within one meter of the space behind the vehicle. The pollution area of more than 24 ppm is approximately 0.124 m2, the pollution length is approximately 0.767 m, and the pollution width and height are 1.16 m and 1.83 m, respectively. In the adjustable range of the research conditions and air speed, the increase in the air speed can accelerate the dilution of CO gas, but it needs to be maintained in a reasonable air speed range. In this paper, a theoretical basis for exploring the migration and distribution of fuel vehicle exhaust pollution in confined spaces is provided.

Impact of human body shape on forced convection heat transfer

Predicting human thermal comfort and safety requires quantitative knowledge of the convective heat transfer between the body and its surrounding. So far, convective heat transfer coefficient correlations have been based only upon measurements or simulations of the average body shape of an adult. To address this knowledge gap, here we quantify the impact of adult human body shape on forced convection. To do this, we generated fifty three-dimensional human body meshes covering 1st to 99th percentile variation in height and body mass index (BMI) of the USA adult population. We developed a coupled turbulent flow and convective heat transfer simulation and benchmarked it in the 0.5 to 2.5m·s-1 air speed range against prior literature. We computed the overall heat transfer coefficients, hoverall, for the manikins for representative airflow with 2m·s-1 uniform speed and 5% turbulence intensity. We found that hoverall varied only between 19.9 and 23.2 W·m-2K-1. Within this small range, the height of the manikins had negligible impact while an increase in the BMI led to a nearly linear decrease of the hoverall. Evaluation of the local coefficients revealed that those also nearly linearly decreased with BMI, which correlated to an inversely proportional local area (i.e., cross-sectional dimension) increase. Since even the most considerable difference that exists between 1st and 99th percentile BMI manikins is less than 15% of hoverall of the average manikin, it can be concluded that the impact of the human body shape on the convective heat transfer is minor.

Study on the distribution characteristics of dust with different particle sizes under forced ventilation in a heading face

Coal mines face a significant situation with regard to dust control. Numerical simulation was used in this paper to study the distribution of dust of different particle sizes in a specific case, as well as the influence of changing the supply airflow velocity on the dust distribution. The findings demonstrate that the airflow primarily migrates from the return air side to the air inlet side and the exit, with the intensity of the airflow decreasing as the distance increases. The amount of dust is high in the area with a strong airflow and low in other areas, and dust of different particle sizes is separated gradually. Increasing the supply air velocity has a greater effect on large dust particles than on small dust particles under the conditions and air speed range studied in this paper. Reasonable reduction of the supply air velocity can effectively reduce the amount of suspended dust.

Combining an active method and a passive method in cooling lithium-ion batteries and using the generated heat in heating a residential unit

In this paper, a gentle air flow is simulated among cylindrical lithium-ion battery (LIIB) cells using COMSOL software. A circular PCM compartment is placed around the battery cells. The hot air from cooling the battery is used to heat the house. By changing the battery position in three modes in PCM in the air speed range of 1 × 10−3 to 5 × 10−3m/s, the volume fraction of solid PCM, the average PCM temperature (TAve−PCM), the maximum battery temperature (Tmax−b) and the exhaust air temperature at different times from 0 to 1000 seconds are analyzed. The percentage of time energy provided by this system of the total energy required for this residential house has also been examined. The results of this study show that over time at high speeds, the Tmax−b of the LIIB first increases and then decreases. The passage of time also reduces the amount of TOutlet. If the LIIB is placed on the air inlet side of the PCM instead of the air outlet side, the Tmax−b is reduced by 1.53 degrees at high speeds. Placing the LIIB on the left side of the PCM causes the output temperature (TOutlet) to be higher and also increases the amount of solid PCM by up to 5% in 1000 seconds compared to placing the LIIB on the right side. Using 50 cells of LIIB and air flow of 0.005 m/s in this system can provide up to 22% of the required energy for heating the building in a winter day.

Custer Channel Wings for Short Takeoff and Landing of Unmanned Aircraft

The channel wing is a lift-enhancement concept pioneered by Willard Ray Custer in the late 1940s in an effort to provide a fixed-wing aircraft with short takeoff and landing (STOL) capabilities. This paper experimentally investigates the possibility of using Custer channel wings for slow flight and STOL of small (under 35 kg) fixed-wing unmanned aerial vehicles. The Custer unmanned aircraft developed at the University of Southampton is introduced in this paper, including details of the installed channel wings and other systems necessary for slow-flight operation. Results from wind-tunnel tests are presented, showing a significant lift increase due to the channel wings in the range of airspeeds of interest. Flight tests are carried out to demonstrate the slow flight and STOL capabilities of the aircraft, showing superior stall characteristics and a two-thirds reduction of the runway length required when using the channel wings. Flight-test comparisons to a conventional wing–propeller configuration show superior slow-flight performance and 7–9% lower cruise speed of the channel-wing aircraft.

Cooling Design for PEM Fuel-Cell Stacks Employing Air and Metal Foam: Simulation and Experiment

A new study investigating the cooling efficacy of air flow inside open-cell metal foam embedded in aluminum models of fuel-cell stacks is described. A model based on a commercial stack was simulated and tested experimentally. This stack has three proton exchange membrane (PEM) fuel cells, each having an active area of 100 cm2, with a total output power of 500 W. The state-of-the-art cooling of this stack employs water in serpentine flow channels. The new design of the current investigation replaces these channels with metal foam and replaces the actual fuel cells with aluminum plates. The constant heat flux on these plates is equivalent to the maximum heat dissipation of the stack. Forced air is employed as the coolant. The aluminum foam used had an open-pore size of 0.65 mm and an after-compression porosity of 60%. Local temperatures in the stack and pumping power were calculated for various air-flow velocities in the range of 0.2–1.5 m/s by numerical simulation and were determined by experiments. This range of air speed corresponds to the Reynolds number based on the hydraulic diameter in the range of 87.6–700.4. Internal and external cells of the stack were investigated. In the simulations, and the thermal energy equations were solved invoking the local thermal non-equilibrium model—a more realistic treatment for airflow in a metal foam. Good agreement between the simulation and experiment was obtained for the local temperatures. As for the pumping power predicted by simulation and obtained experimentally, there was an average difference of about 18.3%. This difference has been attributed to the poor correlation used by the CFD package (ANSYS) for pressure drop in a metal foam. This study points to the viability of employing metal foam for cooling of fuel-cell systems.

Performance enhancement for a magnetic-coupled bi-stable flutter-based energy harvester

This paper aims at presenting a novel magnetic-coupled bi-stable flutter-based energy harvester (MBFEH) for the purpose of enhancing power generation in low speed air flow. The MBFEH comprises of a piezoelectric beam with a magnet on its tip, a hinged rigid flat airfoil, and an external magnet. The magneto-electro-aeroelastic system is theoretically modeled, numerically investigated, and experimentally validated. The influences of the separation distance between the magnets on flutter characteristics and performance of power generation are studied. The numerical and experimental results show that the supercritical flutter will be transformed into the subcritical flutter which realizes a significant reduction of cut-in air speed for energy harvesting. Compared with the conventional flutter-based energy harvester, the cut-in air speed of the MBFEH is reduced by more than 50% when the separation distance is set as 15 mm. The most preferred distance among the tested configurations is 12 mm which broadens the usable air speed by 1.8 m s−1, and leads to a 102% improvement of the energy harvesting performance throughout the air speed region from 2 m s−1 to 6.6 m s−1. The study shows that the proposed MBFEH is an effective design approach for enhancing energy harvesting capability in low air speed range.

Identification and Modeling of the Airbrake of an Experimental Unmanned Aircraft

This paper presents the modeling, system identification, simulation and flight testing of the airbrake of an unmanned experimental aircraft in frame of the FLEXOP H2020 EU project. As the aircraft is equipped with a jet engine with slow response an airbrake is required to increase deceleration after speeding up the aircraft for flutter testing in order to remain inside the limited airspace granted by authorities for flight testing. The airbrake consists of a servo motor, an opening mechanism and the airbrake control surface itself. After briefly introducing the demonstrator aircraft, the airbrake design and the experimental test benches the article gives in depth description of the modeling and system identification referencing also previous work. System identification consists of the determination of the highly nonlinear (saturated and load dependent) servo actuator dynamics and the nonlinear aerodynamic and mechanical characteristics including stiffness and inertia effects. New contributions relative to the previous work are a unified servo angular velocity limit model considering opening against the load or closing with it, the detailed construction and evaluation of airbrake normal and drag force models considering the whole deflection and aircraft airspeed range, the presentation of a unified aerodynamic - mechanic nonlinearity model giving direct relation between airbrake angle, dynamic pressure and servo torque and the transfer function-based modeling of stiffness and inertial effects in the mechanism. The identified servo dynamical model includes system delay, inner saturation, the aforementioned load dependent angular velocity limit model and a transfer function model. The servo model was verified based-on test bench measurements considering the whole opening angle and dynamic load range of the airbrake. New, unpublished measurements with gradually increasing servo load as the servo moves are also considered to verify the model in more realistic circumstances. Then the full airbrake model is constructed and tested in simulation to check realistic behavior. In the next step the airbrake model integrated into the nonlinear simulation model of the FLEXOP aircraft is tested by flying simulated test trajectories with the baseline controller of the aircraft in software-in-the-loop (SIL) Matlab simulation. First, the standalone airbrake simulation is compared to the SIL results to verify flawless integration of airbrake model into the nonlinear aircraft simulation. Then deceleration times with and without airbrake are compared underlining the usefulness of the airbrake in the test mission. Finally, real flight data is used to verify and update the airbrake model and show the effectiveness of the airbrake.

Stall Control by Plasma Actuators: Characterization along the Airfoil Span

A dielectric barrier discharge actuator (DBD) is considered and studied as a stall recovery device. The DBD is installed on the nose of a NACA0015 airfoil with chord × span 300 × 930 mm. The geometry of the exposed electrode has periodic triangular tips purposely designed for the case under study. Wind tunnel tests have been carried out over a range of airspeeds up to 35 m/s with a Reynolds number of 700 k. The flow morphology has been characterized by means of the particle image velocimetry technique, obtaining velocity fields and pressure coefficients. By exploring different planes along the model span, the three-dimensional effect of the DBD has been reconstructed, identifying the flow region mainly sensitive to the plasma actuation. Finally, the actuator effectiveness has been quantified accounting for the power consumption data, leading to defining further design improvements in view of a better efficiency.

The role of convection in electrohydrodynamic drying

Electrohydrodynamic (EHD) drying is a promising way to dehydrate food and other materials. The driving forces of the moisture removal from the product are, however, not yet completely understood. Therefore, a unique experimental setup with a grounded metal mesh collector was designed to separately evaluate the electrical and convective effects of EHD on the drying rate. EHD drying showed significantly higher drying rate (2–2.7 times) compared to purely convective drying at a comparable airspeed range. The direct effect of electrical drivers (electrostatic field and ion flow) on the drying rate was about 30%, while the main effect was due to the EHD-induced convective airflow. To our knowledge, this is the first attempt to separate convective and electrical mechanisms of EHD drying, which is critically important for industrial upscaling of this technology.

Performance Comparison of Quadcopters with Variable-RPM and Variable-Pitch Rotors

Use of variable-pitch rotors was compared against variable-RPM rotors on a 2-kg (20 N) quadcopter in simulation. To generate 5 N of thrust in hover while maintaining a 2:1 maximum thrust-to-weight ratio, the variable-pitch rotor required 29% more power. At low climb rates the variable-RPM rotor requires less power, but near its maximum rate it required more power than the variable-pitch rotor. The maximum climb rate for the variable-pitch rotor was up to 70% greater than that of the variable-RPM rotor. A quadcopter equipped with variable-pitch rotors required more power to operate compared to the aircraft with variable-RPM rotors over its operational airspeed range. The variable-pitch quadcopter required 30% more power at best-endurance speed and had 18% less range than the variable-RPM quadcopter (at maximum-range speed). The 1/rev root drag shear was 42% larger for the variable-RPM rotor, and the 2/rev H- and Y-forces were 37% and 50% larger. The 2/rev thrust vibration was 6.5% smaller for the variable-RPM rotor, and the hub pitching and rolling moments were 11% and 9% smaller, respectively. Unlike the quadcopter equipped with variable-pitch rotors, the quadcopter equipped with variable-RPM rotors experienced a beating phenomenon in the aircraft-level vibratory loads.

Avian surface reconstruction in free flight with application to flight stability analysis of a barn owl and peregrine falcon.

Birds primarily create and control the forces necessary for flight through changing the shape and orientation of their wings and tail. Their wing geometry is characterised by complex variation in parameters such as camber, twist, sweep and dihedral. To characterise this complexity, a multi-view stereo-photogrammetry setup was developed for accurately measuring surface geometry in high resolution during free flight. The natural patterning of the birds was used as the basis for phase correlation-based image matching, allowing indoor or outdoor use while being non-intrusive for the birds. The accuracy of the method was quantified and shown to be sufficient for characterising the geometric parameters of interest, but with a reduction in accuracy close to the wing edge and in some localised regions. To demonstrate the method's utility, surface reconstructions are presented for a barn owl (Tyto alba) and peregrine falcon (Falco peregrinus) during three instants of gliding flight per bird. The barn owl flew with a consistent geometry, with positive wing camber and longitudinal anhedral. Based on flight dynamics theory, this suggests it was longitudinally statically unstable during these flights. The peregrine falcon flew with a consistent glide angle, but at a range of air speeds with varying geometry. Unlike the barn owl, its glide configuration did not provide a clear indication of longitudinal static stability/instability. Aspects of the geometries adopted by both birds appeared to be related to control corrections and this method would be well suited for future investigations in this area, as well as for other quantitative studies into avian flight dynamics.

Determination of a Methodology to Derive Correlations Between Window Opening Mass Flow Rate and Wind Conditions Based on CFD Results

This paper presents a methodology for the development of an empirical equation which can provide the air mass flow rate imposed by single-sided wind-driven ventilation of a room, as a function of external wind speed and direction, using the results from Computational Fluid Dynamics (CFD) simulations. The proposed methodology is useful for a wide spectrum of applications, in which no access to experimental data or conduction of several CFD runs is possible, deriving a simple expression of natural ventilation rate, which can be further used for energy analysis of complicated building geometries in 0-D models or in object-oriented software codes. The developed computational model simulates a building, which belongs to Rheinisch-Westfälische Technische Hochschule (RWTH, Aachen University, Aachen, Germany) and its surrounding environment. A tilted window represents the opening that allows the ventilation of the adjacent room with fresh air. The derived data from the CFD simulations for the air mass flow were fitted with a Gaussian function in order to achieve the development of an empirical equation. The numerical simulations have been conducted using the Ansys Fluent v15.0® software package. In this work, the k-w Shear Stress Transport (SST) model was implemented for the simulation of turbulence, while the Boussinesq approximation was used for the simulation of the buoyancy forces. The coefficient of determination R2 of the curve is in the range of 0.84–0.95, depending on the wind speed. This function can provide the mass flow rate through the open window of the investigated building and subsequently the ventilation rate of the adjacent room in air speed range from 2.5 m/s to 16 m/s without the necessity of further numerical simulations.

Investigation on wavy characteristics of shear-driven water film using the planar laser induced fluorescence method

Aircraft icing poses a serious threat to flight safety. Unfrozen impinging water on the surface of the aircraft will run back under the effect of high-speed airflow, altering liquid distribution and heat transfer characteristics. In this paper, a series of experiments were conducted over a wide range of air speed (Ua = 20.8–56.6 m/s), film Reynolds number (Ref = 26–128) to investigate the dynamics of ultrathin water film on an Aluminum substrate. The analyses of water film thickness and wavy characteristics were conducted through the planar laser-induced fluorescence method, in which the variations of transient characteristics of water film thickness with both the air speed and flow rate were analyzed. The statistics of water film thickness characteristics indicates that, the ratio of surface roughness of water film to its mean thickness is 0.4–0.8. The variation of the wave parameters of gas-liquid interface with both the air speed and the Reynolds number of the water film are also presented and analyzed in detail, including the main frequency of wave, interface wave height, surface wave velocity, interface wave curvature, and wave length parameters. This work is helpful to fundamentally understanding the wavy characteristics of shear-driven water film, as well as optimize the de-icing system for aircraft.

New air speed calibration system at NMIJ for air speeds up to 90 m/s

National Metrology Institute of Japan (NMIJ) has established a high air speed standard facility and has been providing a calibration service since 2015. The facility has an air speed range of 40 m/s to 90 m/s with a relative expanded uncertainty (k = 2) of 0.63%. The purpose of this primary standard is mainly to contribute to the improvement of meteorological observation research and to the evaluation of flow field inside a turbo machine and around a high speed vehicle. The reference air speed is derived from the national primary gas flowrate standard of Japan. A conversion device from flowrate to air speed is installed in the test line of the closed-loop calibration facility. The reference air speed at the nozzle exit of the conversion device is obtained by comparing the integral of the air speed profiles and the reference volume flowrate. The total pressure tube used as a transfer standard is then calibrated against the reference air speed at the center of the nozzle exit. The Eiffel-type wind tunnel, which is a working standard for the daily calibration service, is calibrated using this total pressure tube. The present paper describes the calibration system, the traceability chain, and an uncertainty analysis using a validation method.

Ground Flutter Simulation Test Based on Reduced Order Modeling of Aerodynamics by CFD/CSD Coupling Method

Flutter is an aeroelastic phenomenon that may cause severe damage to aircraft. Traditional flutter evaluation methods have many disadvantages (e.g., complex, costly and time-consuming) which could be overcome by ground flutter test technique. In this study, an unsteady aerodynamic model is obtained using computational fluid dynamics (CFD) code according to the procedure of frequency domain aerodynamic calculation. Then, the genetic algorithm (GA) method is adopted to optimize interpolation points for both excitation and response. Furthermore, the minimum-state method is utilized for rational fitting so as to establish an aerodynamic model in time domain. The aerodynamic force is simulated through exciters and the precision of simulation is guaranteed by multi-input and multi-output robust controller. Finally, ground flutter simulation test system is employed to acquire the flutter boundary through response under a range of air speeds. A good agreement is observed for both velocity and frequency of flutter between the test and modeling results.

A novel design for an adaptive aeroelastic energy harvesting system: flutter and power analysis

Extracting energy from waste sources could be a new prospect toward energy crisis, specially from wind energy. A simple mechanical system, including mass and spring, if combined with a wing, could extract more energy. A novel design for a cantilever beam with an airfoil is presented in this paper for harvesting more energy. This design allows the harvester to operate in a wider range of airspeeds. Electrical energy will be extracted from a piezoelectric patch on the beam. This novel design moves a point mass along the beam regarding the airspeed because this movement might compromise between flutter occurrence and more energy extraction. In order to understand this compromise, the effect of the position of the point mass on the onset of flutter instability and output power of the system is investigated. Mathematical models include both linear and nonlinear aeroelastic models. For flutter analysis, a linear model called finite state model is used. The nonlinear part of the problem is modeled by ONERA dynamic stall model. A parametric study is conducted in order to have a better understanding of design criteria. Both flutter onset airspeed and output power are achieved for ten different places of the point mass on the beam. According to the results, a passive mass-positioning system could be able to set the position of the point mass for any given airspeed. Based on these results, a proper passive mechanism is designed including a set of springs, strings, guiding rails, pulleys, and a parachute. The aeroelastic model used in this paper is validated by experiments of the state of the art. The novel mechanism in this design-oriented paper continues the concepts and experiments, presented in the literature.