Drag Values Research Articles

Wind Tunnel Balance Measurements of Bioinspired Tails for a Fixed Wing MAV

Bird tails play a significant role in aerodynamics and stability during flight. This paper investigates the use of bioinspired horizontal stabilizers for Micro Air Vehicles (MAVs) with Zimmerman wing-body geometry. Five configurations of bioinspired horizontal stabilizers are presented. Then, 3-component external balance force measurements of each horizontal stabilizer are performed in the wind tunnel. The Squared-Fan-Shaped Horizontal Stabilizer (HSF-tail) is selected as the optimal horizontal stabilizer that provides the highest aerodynamic efficiency during cruise flight while maintaining high longitudinal stability on the vehicle. The integration of the HSF-tail increases the aerodynamic efficiency by more than 6% up to a maximum of 17% compared to the other alternatives while maintaining the lowest aerodynamic drag value during the cruise phase. Furthermore, balance measurements to analyze the influence of the HSF-tail deflection on the aerodynamic coefficients are conducted, resulting in increased lift force and reduced aerodynamic drag with negative tail deflections. Lastly, the experimental data is validated with CFD-RANS steady simulations for low angles of attack, obtaining a relative difference on the measurement around 5% for the aerodynamic drag coefficient and around 10% for the lift coefficient during the cruise flight that demonstrates a high degree of accuracy in the aerodynamic coefficients obtained by external balance in the wind tunnel. This work represents a novel approach through the implementation of a horizontal stabilizer inspired by the structure of the tails of birds that is expected to yield significant advancements in both stability and aerodynamic efficiency, with the potential to revolutionize MAV technology.

Исследование влияния химического состава воздушной среды на аэродинамику полета малых летательных аппаратов

The work is devoted to the study of the influence of an air environment with different chemical composition on the aerodynamics of small aircrafts of the airplane type used for reconnaissance purposes in case of fires. The thermodynamic properties of the combustion products formed during the combustion of rubber and foam rubber were calculated. The properties of the medium were taken into account in the mathematical modeling of the flight aerodynamics of an unmanned aerial vehicle. The mathematical model is based on solving conservation equations in a non-isothermal formulation for a turbulent viscous compressible flow using the k-ε turbulence model. The pressure and velocity fields of the environment were obtained during the flow around the wing, and the values of drag and lift forces were compared in the presence of combustion products in the air and without them. In particular, the numerical calculations were carried out in the presence of a vertical temperature gradient in the design area simulating the heating of air masses during fires with the study of the influence of these gradients on the aerodynamic characteristics of the wing. The calculations show that with an increase in the vertical temperature gradient by 60 K/m, the values of lift and drag decrease by 5 %.

Large eddy simulations (LES) of a three-element high-lift wing: Exploring the active flow control (AFC) capabilities

This study presents an aerodynamic analysis of the 30P30N high-lift three-element wing under varying the angle of attack (α = 5°, 9°, and 23°) at a constant Reynolds number (Rec = 750, 000) by means of large eddy simulations (LES). Baseline results were validated against existing literature, demonstrating good agreement. The increase of the angle of attack entails higher values of lift but also, increased values of drag. At α = 23°, a recirculation area appears above the flap, this being the signature of the stall conditions. This is related to the adverse pressure gradient that develops along the main suction side and the separation of the streamlines in its wake. Actuation strategies using synthetic jets were explored to mitigate this flow separation at this angle of attack, and thus, enhance the efficiency of the wing. Three actuation cases with the jets located on the main wing, on the flap, and on both elements at the same time were investigated. While some improvements are observed with the actuation, particularly in the combined actuation case, the overall wing efficiency was only marginally enhanced. Challenges in achieving significant improvements were attributed to complex flow interactions and the dominance of pressure forces, which affect both the lift and the drag coefficients at the same time.

Estimating Active Drag Based on Full and Semi-Tethered Swimming Tests.

During full tethered swimming no hydrodynamic resistance is generated (since v = 0) and all the swimmer's propulsive force (FP) is utilized to exert force on the tether (FT = FP). During semi-tethered swimming FP can be made useful to one of two ends: exerting force on the tether (FST) or overcoming drag in the water (active drag: Da). At constant stroke rate, the mean propulsive force (FP) is constant and the quantity FP - FST (the "residual thrust") corresponds to Da. In this study we explored the possibility to estimate Da based on this method ("residual thrust method") and we compared these values with passive drag values (Dp) and with values of active drag estimated by means of the "planimetric method". Based on data obtained from resisted swimming (full and semi-tethered tests at 100% and 35, 50, 60, 75, 85% of the individual FT), active drag was calculated as: DaST = kaST.vST2 = FP - FST ("residual thrust method"). Passive drag (Dp) was calculated based on data obtained from passive towing tests and active drag ("planimetric method") was estimated as: DaPL = Dp.1.5. Speed-specific drag (k = D/v2) in passive conditions (kp) was )25 kg.m-1 and in active conditions (ka) )38 kg.m-1 (with either method); thus, DaST > Dp and DaST > DaPL. In human swimming active drag is, thus, about 1.5 times larger than passive drag. These experiments can be conducted in an ecological setting (in the swimming pool) by using basic instrumentation and a simple set of calculations.

Fluid-structure Interaction Study on Drag Characteristics of Flexible Ribbon

The flexible ribbon can be used as a projectile stabilizing device to provide a stable moment for the projectile, and the research on its drag characteristics is of great significance. This paper uses the arbitrary Lagrange-Euler (ALE) method to simulate the fluid-structure interaction process of the ribbon swinging in the airflow. The numerical method is validated by comparing it with wind tunnel experimental results from previous literature. This study utilized numerical simulation to investigate the impact of inflow velocity, ribbon material properties, and ribbon shape on drag characteristics. The research concluded that for a single ribbon, the drag value increases as the incoming flow velocity, ribbon material density, elastic modulus, and length-width ratio increase. In addition, the drag value of the annular ribbon is greater than that of the double ribbon. The drag values of the double ribbon and the annular ribbon are averaged to one side, the unilateral drag of the annular ribbon is greater than that of the single ribbon, and the unilateral drag of the double ribbon is smaller than that of the single ribbon. The conclusions can provide a reference for studying flexible ribbon stabilized projectiles.

A Study on Oscillatory Micropolar Flow Beyond a Contaminated Micropolar Fluid Sphere

In this paper, the hypothesis of the axisymmetric rectilinear oscillatory flow beyond a micropolar tainted fluid sphere particle in an incompressible non-Newtonian fluid and also the axisymmetric rectilinear oscillatory flow over a viscous tainted fluid sphere particle in an incompressible Newtonian fluid with small amplitude oscillations have been investigated. The velocity field is exhibited in terms of stream functions, and a slip condition is considered on the boundary. The fluid velocities and microrotation components were derived through analytical procedure. The drag force acting on the particle was also computed and verified for special cases. The real drag and imaginary drag values are numerically extracted for varying slip parameter i.e., 2≤s≤30, micro polarity i.e., 8≤e≤32 , and viscosity ratio i.e., 5≤μ≤20 at a fixed parameter values k=0.1,ρ=0.6,ω=0.6,t=0.6. Graphs and tables are used to display the numerical results. It was observed that there was an inverse proportion between slip parameter values, real drag and direct proportion between slip parameter and imaginary drag, for different viscosity ratio and micro polarity values.

A Detailed Numerical Study on Aerodynamic Interactions of Tandem Wheels on a Generic Vehicle

Wheels contribute significantly to the aerodynamic performance of ground vehicles. Many studies have focused on investigating a single wheel either in isolation or in a wheelhouse. However, there has been less focus on the flow field around a rear wheel, especially when considering varying proximity to the front wheel, despite its importance on aerodynamic forces. In this study, a generic reference body is modified and fitted with a rear wheel within a wheelhouse and analysed while the wheel spacing varies. Reynolds-Averaged Navier–Stokes (RANS) modelling was employed to allow for multiple variations to be considered and the model produced results in good agreement with experimental results. The results confirm that two upper rear wheelhouse outflow vortices are only present when the wheel spacing is short. It was found that the drag values were minimal for the wheel spacing at a critical distance of 1.5 wheel diameters. At this wheel spacing, the formation of the outboard jetting vortex is prevented at the rear wheel, and hence, the rear wheel drag is reduced by more than 10%. Any further reduction in the spacing does not provide any drag benefits. Also, the outflow from the front wheelhouse is projected further away from the body, drawing flow from the rear wheelhouse into the outboard jetting vortex.

On the spurious effects in Lamb-vector-based force decomposition methods

Recent methods based on Lamb vector integration allow for a far-field formulation and decomposition of the whole aerodynamic force, with identification of local flow structures associated with the force generation. Different exact Lamb-vector-based force formulations were proposed in the past and the decomposition of total drag into lift-induced and parasite contributions was subject of very recent studies. However, inconsistencies were also reported, raising questions on the physical role of a non-zero induced drag found in two-dimensional flows. Moreover, the effect of the arbitrary pole (appearing in Lamb-vector-based formulas) on the numerical accuracy of such methods was never investigated. Additionally, the separation of parasite drag into viscous and wave drag contributions by Lamb vector field analysis is still questioned. In this paper, the accuracy of different force formulas and of the drag decomposition in lift-induced and parasite contributions is first analyzed, for steady flows. Two-dimensional numerical solutions around RAE2822 and NACA0012 airfoils are considered, the latter in both inviscid and viscous flows (at low and high Reynolds number), to analyze consistency between lift-induced/parasite drag definitions and the drag generated in isentropic flow conditions (reversible drag) or due to entropy production (irreversible drag). A spurious induced drag contribution (related to the streamwise momentum perturbation) is identified, resulting in negative induced drag values in two-dimensional flows. The effect of a shift in the pole location is also analysed, with reference to its impact on the total force and on drag decomposition accuracy, then a new approach to parasite drag breakdown into physical constituents (viscous and wave contributions) is proposed and results are compared against predictions obtained using consolidated thermodynamic-based methods and against available results from recent literature.

Assessment of Computational Fluid Dynamics Reynolds-Averaged Navier–Stokes Models for Bluff Bodies Aerodynamics

<div>Since the steady-state computational fluid dynamics (CFD) Reynolds-averaged Navier–Stokes (RANS) turbulence models offer low-cost and sensible accuracy, they are frequently utilized for bluff bodies’ external aerodynamics investigations (e.g., upwind, crosswind, and shape optimization). However, no firm certainty is made regarding the best model in terms of accuracy and cost. Based on cost and accuracy aspects, four RANS turbulence models were studied, which are Spalart–Allmaras, realizable k-ε, RNG k-ε, and SST k-ω. Ahmed body with a 25° slant angle benchmark case was introduced for this investigation. Two grids were generated to satisfy the near-wall treatment of each turbulence model. All grid settings were proposed and discussed in detail. Fluid-structure analysis was performed on five different planes. Regarding flow field prediction, realizable k-ε and renormalization group (RNG) k-ε models demonstrated a remarkable consistency with experimental data, while Menter’s shear stress transport (SST) k-ω showed a poor agreement. The obtained computational values of drag and lift coefficients were compared with experimental results. All investigated RANS turbulence models had reported results in excellent agreement with experimental drag coefficient values. The SST k-ω model has underestimated lift coefficient value with an error of about −45% with experimental value. Only realizable k-ε and RNG k-ε presented an error <10% for predicting drag and lift coefficients.</div>

Studying Modern Formula 1 Front Wing at High Cornering Speeds

A simulation-based study of three different types of front wing designs used in modern Formula 1 cars was done. The study mainly focuses on the aerodynamic forces that a Formula One car generates mainly the Downforce, the Drag force, & the Lateral force at high cornering speeds. These forces were studied in detail & taking a closer look at how they migrate during the dynamic conditions the car is thrown at various Side Slip (Yaw) Angles, these results were compared with the wing Scuderia Ferrari used in the 1998 Formula 1 championship to better understand the inherent problems faced in those previous designs. A brief study of the flow field & flow lines was conducted along with the vortex generation for all three wings. Vortex formation and management is a prominent part of research being carried out for a Formula 1 car, so a brief study on the phenomenon of vortex generation & Y250 vortex formation was also carried out. The studies were carried out over typical high-speed corners where the speed ranges between 220-300 KM/Hr. A study on the effect of the flow field of the top element on the lower element was carried out where the 5th element was removed from each of the three wings & the effect on the downforce & drag value was analysed along with the pressure field.
 Keywords: Modern formula 1, Front wing designs, Cornering speeds, aerodynamic forces, Side Slip (Yaw) Angles, Centre of pressure (CoP), Lateral force, CFD, Downforce

Steady Bi-dimensional Crossflow Plasma Jets in Turbulent Channel Flows

In this study, the possibility of reducing the friction drag exerted by turbulent flows by means of wall-mounted plasma actuators is experimentally investigated. Two large plasma actuators (PAs) arrays were operated in a channel-flow facility. They were conceived to replicate, the flow control approach investigated by Mahfoze and Laizet (Int J Heat Fluid Flow 66:83–94, 2017) by means of numerical simulations. Namely, steady and relatively largely spaced (378 wall units) actuators were lain down such to induce stationary crossflow-directed fluid motions. Different actuation parameters (actuators’ configurations and supplied voltages) and flow Reynolds numbers were tested. Flow static pressure measurements were performed along with the actuators mechanical and electrical characterization. The resulting values of drag manipulation and actuation efficiency are reported. The tested flow actuation led to overall higher values of flow friction drag, whereas values overcoming the value of 30% of drag reduction were measured at the more downstream actuation positions. The discrepancy with the above reference is deemed to be mainly due to the finite flow actuation hereby considered. Nevertheless, a slightly different Reynolds number was here considered while the actuators effect was measured to be considerably weaker.

Flow simulation around square cylinder with inclined corner gap at low Reynolds number

In this paper, an investigation of the effects of inclined corner gaps of varying widths and lengths on the static aerodynamic force coefficients and flow features of a square cylinder at low Reynolds number (Re of 100) by comparing with an unmodified square cylinder is discussed. The width of the corner gap (x/D) was varied between 0.02 and 0.24, with two different lengths of it (l/D), namely, 0.05 and 0.11. The open-source code OpenFOAM was used as a solver. A second-order accuracy level was ensured for both time and space during the numerical set up of the model. Validation and verification studies were conducted to ensure the authenticity of the results. The mean and rms values of the static force coefficients of these cylinders were compared and important flow features were explored. Even at a low Re, the proposed corner modification was found to be effective in improving the static aerodynamic performance. For different gap widths, the static force parameters evidenced some patterns, with an optimum width for which the mean drag value reached the minimum value identified. Furthermore, the mean and fluctuating pressure and velocity contour were analyzed to understand the underlying flow mechanism.

Lattice Boltzmann Computation of Steady Cross-Flow Across a Rectangular Obstacle with Different Aspect Ratio: Effect of Blockage Ratio

This work presents a two dimensional lattice Boltzmann analysis of steady and cross-flow of New tonian fluid across a built-in rectangular cylinder. In particular, the effects of the blockage ratio and aspect ratio of rectangular cylinder (width/height) on the momentum characteristics have been explored for range of flow governing parameters such as, blockage ratio (β = 1/8, 1/12, 1/16), aspect ratio of rectangular cylinder (1 ≤ a_r ≤ 6) at constant Reynolds number of Re = 40 corresponding to the laminar range. The physical insight of system is gained by evaluation of stream-function, vorticity and pressure coefficient variation, etc. Further, the engineering gross parameter, such as drag coefficient is determined for possible use in engineering design purpose. It is observed that the increase in blockage ratio drag coefficient values decreases and drag values show proportional variation with aspect ratio. Finally, a closure relationship is developed between drag coefficient, blockage ratio and aspect ratio of rectangular cylinder for possible use in engineering/scientific practices

A novel method of determining the active drag profile in swimming via data manipulation of multiple tension force collection methods

A novel method aimed at evaluating the active drag profile during front-crawl swimming is proposed. Fourteen full trials were conducted with each trial using a stationary load cell set-up and a commercial resistance trainer to record the tension force in a rope, caused by an athlete swimming. Seven different stroke cycles in each experiment were identified for resampling time dependent data into position dependent data. Active drag was then calculated by subtracting resistance trainer force data away from the stationary load cell force data. Mean active drag values across the stroke cycle were calculated for comparison with existing methods, with mean active drag values calculated between 76 and 140 N depending on the trial. Comparing results with established active drag methods, such as the Velocity Perturbation Method (VPM), shows agreement in the magnitude of the mean active drag forces. Repeatability was investigated using one athlete, repeating the load cell set-up experiment, indicating results collected could range by 88 N depending on stroke cycle position. Variation in results is likely due to inconsistencies in swimmer technique and power output, although further investigation is required. The method outlined is proposed as a representation of the active drag profile over a full stroke cycle.

Investigation on the opposing jet penetration mode transition mechanism in the hypersonic flow

Abstract As an effective drag reduction and thermal protection technology, the opposing jet can guarantee the flight safety of the hypersonic vehicle. In this paper, the jet mode transition is realised by controlling the total jet pressure ratio value (PR) with a function. The jet mode transition from the long penetration mode (LPM) to the short penetration mode (SPM) uses an increasing function. However, the jet mode transition from SPM to LPM uses a decreasing function. The flow field reconstruction process of a two-dimensional axisymmetric blunt body model in the hypersonic flow is studied when the jet mode transition between SPM and LPM changes into each other. The flow field structures and wall parameters of the LPM and SPM transition processes are obtained. The results indicate that the drag and Stanton number both decrease in the transition stage from LPM to SPM, and this is beneficial for the improvement of the drag reduction and thermal protection effect. The peak values of drag and Stanton number fall by 36.39% and 46.40%, respectively. When the jet mode transforms from SPM to LPM, the Stanton number increases, and the drag force first increases and then decreases. However, the final drag reduction effect is not obvious. With the increase in the change rate of the total pressure ratio of the two jet transformation modes, the jet mode transition time is advanced, and the flow field changes more violently.

CFD Study of Base Drag of the Grot Rocket

Abstract Propulsion system operation is known to affect the aerodynamic characteristics of rockets. Specifically, the net axial force acting on a rocket in flight cannot be precisely obtained by combining the static thrust with drag values computed for a rocket with an inactive motor. One of the main reasons for this is the influence of motor operation on pressure at the base of the rocket. The aim of this paper is to investigate the effect of motor operation on the aerodynamic parameters of the Grot sounding rocket developed by the Students’ Space Association, Warsaw University of Technology. The study consists of two series of axisymmetrical computational fluid dynamic simulations of flow around the rocket – one with the motor being non-operational and the other with active thrust. In the post-processing phase, the axial force acting on various components of the rocket is computed, with an emphasis on the base and nozzle exit sections. Quantitative and qualitative differences between the cases with and without active thrust are highlighted and discussed. The obtained results are compared to a semi-empirical model found in the literature. Finally, a semi-empirical base drag model is proposed for use in Grot flight simulation.

Numerical study of hydrodynamic forces of nonlinear fluid flow in a channel-driven cavity: Finite element-based simulation

This communication is aimed at presenting the flow behavior of viscoplastic materials in a channel driven-cavity by utilizing the Bingham constitutive equation in conjunction with the modification proposed by Papanastasiou. The whole system has been represented by a model consisting of coupled nonlinear partial differential equations. In addition, the governing equations were nondimensionalized by making use of the appropriate set of variables and the computations were carried out using the finite element method. A finite element space including quadratic polynomial [Formula: see text] is chosen for the approximation of velocity profiles whilst a space containing linear polynomials is used for the estimation of pressure [Formula: see text]. The hydrodynamics forces like drag and lift values on cylindrical obstacle whose center is located at (1.5, 1.5) are computed against various values of Bingham number. Moreover, pressure drop values between the back and front of the square obstacle have also been tabulated.

Enhancing the Dynamic Stability of Pylons via Their Drag and Lift Coefficients by Finite Volume Method

This study aimed to estimate the drag and lift coefficients of the long-span bridge pylon using the finite volume method (FVM). The k-ω turbulence model was applied to analyze the behavior of wind flow around the pylon, yielding drag and lift coefficient values with an error of 0.98% compared to a previous tunnel experiment. Four recommended cross-sections were proposed to reduce drag and lift forces acting on the pylon, including concave, convex, crossing, and chamfering cross-sections. The finding indicated that drag and lift coefficient decreased for all cross-sections. Cutting edges of concave, convex, and chamfering cross-sections with a ratio ranging from 0.2 to 0.3 has the greatest impact on reducing drag coefficient, while the crossing cross-section with a cutting ratio ranging from 0.2 to 0.25 has the lowest drag coefficient. The maximum reduction in drag and lift coefficients were 23.69% and 13.14% for concave and chamfering cross-sections. Thus, cutting edges of cross-sections is an effective method to enhance the aerodynamic stability of the pylon. Additionally, we evaluated drag and lift coefficients for different wind direction angles. The angles of 0, 30, and 90 degrees resulted in the highest drag coefficient, while the angle of 0 degrees and the angle of 90 degrees resulted in the lowest and highest lift coefficient, respectively. This study not only provides recommendations for cross-sections that reduce forces acting on the pylon but also provides the intensity of this reduction through corresponding estimation equations. In conclusion, concave and chamfering cross-sections are the most effective in reducing drag and lift coefficients, or, in other words, increasing the aerodynamic stability of the pylon.

Studying Modern Formula 1 Front Wing at Low Cornering Speeds

A simulation-based study of three different types of front wing designs used in the modern Formula 1 cars was done. The study mainly focuses on the aerodynamic forces that a Formula One car generates mainly the Downforce, the Drag force, & the Lateral force at low cornering speeds. These forces were studied in detail & taking a closer look at how they migrate during the dynamic conditions the car is thrown at various Side Slip (Yaw) Angles, these results were compared with the wing Scuderia Ferrari used in the 1998 formula 1 championship to better understand the inherent problems faced in those previous designs. A brief study of the flow field & flow lines was conducted along with the vortex generation for all three wings. Vortex formation and management is a prominent part of research being carried out for a formula 1 car, so a brief study on the phenomenon of vortex generation & Y250 vortex formation was also carried out. A test on ride height and vorticity was also studied when the ride height was varied and the values were analysed. A study on the effect of the flow field of the upper element on the lower element was carried out where the 5th element was removed from each of the three wings & the effect on the downforce & drag value was analysed along with the pressure field.

Aerodynamic performance characteristics of winglet configurations for the low and medium Reynolds number operations

Three-dimensional numerical simulation-assisted parametric evaluation of winglet design for the small unmanned aerial vehicles (UAV) has been performed at low range and medium range of Reynolds number (Re) using commercial CFD package, Ansys-Fluent. By systematic variation of winglet parameters: sweep back and cant angle, the selection of optimum value of these parameters had to be selected for achieving better values of [Formula: see text]/[Formula: see text] and [Formula: see text]/[Formula: see text] to minimize the drag and maximize the range and endurance. Out of these geometrical winglet parameters, by varying one winglet parameter while keeping other parameter as a constant, different sets of winglet configuration have been developed and the detailed representation of semi-wing with winglet geometry has been generated using Computed-Aided Design (CAD) tool. The computational domain has been solved for the Re of [Formula: see text] and [Formula: see text] using “3D Reynolds Averaged Navier–Stokes equations” along the turbulence model, k-[Formula: see text] for all wing configurations with and without winglet planned for this study. From Lift and Drag values for each angle of attack (AOA), [Formula: see text] and [Formula: see text] have been estimated for identifying optimum value of [Formula: see text]/[Formula: see text] and [Formula: see text]/[Formula: see text] to have maximum range and endurance with minimum drag during the cruise operation of small UAVs in low and medium Re range operation. Out of all wing with winglet configurations considered here, the winglet with cant of 70° and 90° results in ending up with better aerodynamic performances for providing better range and endurance. At the same time, the change in sweep angle of the winglet does not show any variation, in turn there is a decrease in aerodynamic performance.