Pitching Moment Coefficient Research Articles

Investigation of a Light Boxplane Model Using Tuft Flow Visualization and CFD

In this paper, we addressed the flow patterns over a light boxplane scale model to explain the previously discovered disagreement between its predicted and experimental aerodynamic characteristics. By tuft flow and CFD visualization, we explored the causes yielding a large zero lift pitching moment coefficient, lateral divergence, difference in fore and aft elevator lift, and poor high lift performance of the aircraft. The investigation revealed that the discrepancy in the pitching moment coefficient and lateral stability derivatives can be attributed to insufficient accuracy of the used predictive methods. The difference in fore and aft elevator lift and poor high lift performance of the aircraft may occur due to the low local Reynolds number, which causes the early flow separation over the elevators and flaperons when deflected downward at angles exceeding 10°. Additionally, some airframe changes are suggested to alleviate the lateral divergence of the model.

Numerical investigations of vortex formation on a generic multiple-swept-wing configuration

For an improvement of the flight stability characteristics of high-agility aircraft, the comprehension of the vortex development, behavior and break down is important. Therefore, numerical investigations on low aspect ratio, multiple-swept-wing configurations are performed in this study to analyze the influence of the numerical method on the vortex formation. The discussed configurations are based on a triple- and double-delta wing planform. Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations and delayed detached eddy simulations (DDES) are performed for both configurations. The simulations are executed at Re = 3.0times 10^6, symmetric freestream conditions, and an angle of attack of alpha = 16^circ, for consistency with reference wind tunnel data. For the triple-delta-wing configuration, the results of the DDES show a satisfying accordance to the experiments compared to URANS, especially for the flow field and the pitching moment coefficient. For the double-delta-wing configuration, the URANS simulation provides reliable results with low deviation of the aerodynamic coefficients and high precision for the flow field development with respect to the experimental data.

Investigation of aerodynamic characteristics of NACA0012 airfoil design using parabolic arcs

An investigation of the pitching moment coefficient has been performed numerically for NACA0012 airfoil design in this paper. The evaluation of the aerodynamic parameter has been analyzed with various ranges of Reynolds number from lower to higher (104 < Re <105). An essential aerodynamic parameter, the pitching moment coefficient is associated with torque developed by the aerodynamic forces around the airfoil design. A novel method of higher order triangular element meshing around the airfoil design has been utilized for the present analysis. The higher order triangular meshing is efficiently performed around the airfoil by incorporating the parabolic arcs of a one-sided curved triangular element. The curved triangular element satisfies the sub-parametric transformation of finite elements. Three different triangular elements such as linear, quadratic, and cubic elements have been considered to mesh around the NACA0012 airfoil design by MATLAB code. The higher order element has proved its efficiency in analyzing the parameter with less computational time and effort which is essential to enhance the performance of aerodynamic structures.

A development of longitudinal static stability analysis method of a Wing-In-Ground effect vehicle in cruise during the design process

Traditional methods of Wing-In-Ground effect (WIG) vehicle longitudinal stability analysis in cruise are based on calculation of aerodynamic forces and moments coefficients and its derivatives. Static longitudinal stability analysis includes the determination of Irodov criteria, and functions of pitch moment coefficient versus lift force coefficient for constant angle of attack or ground clearance are considered as linear. Here the problem of development of WIG vehicle longitudinal static stability analysis method accounting the nonlinearity of pitch moment coefficient on lift force coefficient dependence for constant angle of attack is researched. WIG vehicle aerodynamic characteristics are determinate by RANS-SST numerical simulation. Results of numerical studies show that function of pitch moment coefficient versus lift force coefficient for constant angle of attack is approximated by curve of order no higher than two, and this function for constant ground clearance is linear. The relationship between static height stability, second derivative of the pitching moment coefficient with respect to lift force coefficient, and lift coefficient was derived. Reliability of analysis method is based on using of fundamental equations of WIG vehicle motion and fluid dynamics. Application of the method can simplify study of WIG vehicle stability during design process.

Aeroelastic simulations of a delta wing with a Chimera approach for deflected control surfaces

A numerical tool for the computation of aircraft control surface aerodynamics with flexibility effects is presented. The solution is based on coupled Computational Fluid Dynamics (CFD) and Computational Structural Mechanics (CSM) simulations embedded in the multidisciplinary simulation environment SimServer. In SimServer, the DLR-TAU Code is utilized to obtain the CFD solution by solving the Reynolds-Averaged Navier–Stokes (RANS) equations. Structural displacements are computed with a modal solver. The Chimera implementation of SimServer, suited for hybrid grids, is applied to model the control surfaces. Numerical simulations with the flexible Chimera method are performed for the Model53 wing configuration, which is a generic delta wing with a deployed slat as well as an inboard and outboard trailing edge flap. Aerodynamic and aeroelastic simulations at high dynamic pressure q=45 kPa and transonic speed {text {Ma}} = 0.8 are performed for several angles of attack 10^circ le alpha le 25^circ and flap deflection angles -30^circ le delta le 30^circ. The effect of structural deformations on the flow field and control surface effectiveness are analyzed and compared to computations of components treated fully rigid. At the targeted freestream condition M=0.8 and {text {Re}}=15.1 times 10^7, the flow field around the Model53 configuration is characterized by the interaction of vortices and shock waves. The results of the lift and pitching moment coefficient for the rigid and flexible configuration revealed the importance of taking the structural flexibility into account in order to obtain more accurate results for the considered range of flap deflections. Furthermore, the computational effort of the aerodynamic and aeroelastic simulations are evaluated. The increase in computational effort is shown to be adequate for the given increase in accuracy.

Hypersonic Flow Control of Kinzhal Missile via Off-Axis, Pulsed Energy Deposition

The interaction of an off-axis, spherical energy discharge with the Kh-47M2 Kinzhal missile at Mach 6 sea-level conditions was simulated. A parametric study of the energy discharge parameter (proportional to the ratio of the energy added to the internal energy within the energy deposition volume) was performed to examine the effect of energy added to the heated region in front of the missile and the changes it causes on the drag force, side (vertical) force, and pitching moment. The peak value for the pitching moment coefficient was shown to be 0.0045 for , which was shown to be 15.5% of the value due to a 10° front finset deflection. Both inviscid and Reynolds-averaged Navier–Stokes simulations were performed. The additional influence of the turbulent boundary layer on the peak value of the produced pitching moment was negligible. The time interval for the variation in the pitching moment coefficient due to energy deposition is 61 times faster than the standard actuation time (0.1 s) for conventional control surfaces, indicating the potential for multiple pulsed energy depositions as a means for hypersonic flight control.

Numerical aerodynamic analysis of a reflexed airfoil, N60R, in ground effect with regression models

Flight in the vicinity of the ground is known to be more efficient than flight in a free air stream. However, a nose-down pitching moment created by a typical cambered airfoil generally increases due to ground effect. Thus, a larger tail for the aircraft is required to remain stable, which creates more drag and reduces the efficiency. The pitching moment in the ground effect becomes more complicated because it varies with height above the ground. Thus, the reflexed or S-shaped airfoil was introduced to overcome this effect. The addition of reflex reduces the lift of the airfoil, but it is required for improved stability. This study applied computational fluid dynamics to investigate the aerodynamic characteristics of a reflexed airfoil, N60R, in ground effect over a range of angles of attack from 0° to 20° at a Reynolds number from 0.8106 to 5106 and ground clearance from 5% to 150% of the chord. The numerical results reveal that the boundary layer close to the ground affects the lift, drag, pitching moment coefficients, and center of pressure. As the airfoil operates close to the ground, the lift increased due to a higher pressure build up under the airfoil. Except for a relatively low angle of attack (less than 2°), the lift decreases with a reduction in ground clearance due to loss of upper surface suction. The maximum lift-to-drag ratio, approximately 120, occurred at an angle of attack of 6° and ground clearance of 5%. In summary, this study presents the aerodynamic characteristics of the reflexed airfoil, N60R, over a wide range of angles of attack, Reynolds numbers and ground clearance. Furthermore, regression models for each characteristic were developed and can be used to predict the coefficients of the N60R without the need for consuming time in Computational Fluid Dynamics (CFD) analysis.

INFLUENCE OF SURFACE ROUGHNESS ON THE DYNAMIC STALL OF A ROTARY WING SECTION IN SUBSONIC FLOW

Wear involves the losses of some material from the surface and leads to the surface roughness. In the present work, the influence of surface roughness on the dynamic stall of a rotary wing section in subsonic flow has been investigated with different degree of surface roughness. The airfoil surface roughness was estimated using arithmetic mean roughness value (ISO-4287/1). For this purpose an indicial response method for unsteady, two dimensional flow is used to calculating the unsteady lift and pitching moment of NACA 0012 airfoil undergoing a pitching oscillation in the deep dynamic stall regime. Using the ANSYS-5.8 software as a source for the preliminary static data that required by the indicial method. The investigation is done through a number of test cases with different mean angles of attack, amplitude and reduced frequencies for airfoil oscillating around its quarter chord axis. The results include the time dependent behaviour and hysteresis loops of the lift and pitching moment for the airfoil with different degree of surface roughness. For rough airfoil an aerodynamic characteristic showed a reduction in the lift coefficient, separation point moved forward to the leading edge, the boundary layer reattachment take place at smaller angle of attack, the stall angle decrease and the pitching moment coefficient decrease as compared with smoother airfoil. So the periodic test must be done and re-coating the rotary wing if the surface roughness increased.

The effect of perforation on aerodynamic characteristics and the vortex flow field around a flat plate

The aim of the present investigation is to obtain and analyse vortex flow field and aerodynamic characteristics of perforated plates at different angles by numerical simulation using OpenFOAM software package. For fully perforated plate’s passive gas injection through the holes close to the leading edge induce separation zone deformation and affect the whole flow structure downstream. Perforation along the leading edge tends to result in more monotonous curves of normal force and pitching moment coefficients.

New Aerodynamic Studies of an Adaptive Winglet Application on the Regional Jet CRJ700.

This study aims to evaluates how an adaptive winglet during flight can improve aircraft aerodynamic characteristics of the CRJ700. The aircraft geometry was slightly modified to integrate a one-rotation axis adaptive winglet. Aerodynamic characteristics of the new adaptive design were computed using a validated high-fidelity aerodynamic model developed with the open-source code OpenFoam. The aerodynamic model successively uses the two solvers simpleFoam and rhoSimpleFoam based on Reynold Averaged Navier Stokes equations. Characteristics of the adaptive winglet design were studied for 16 flight conditions, representative of climb and cruise usually considered by the CRJ700. The adaptive winglet can increase the lift-to-drag ratio by up to 6.10% and reduce the drag coefficient by up to 2.65%. This study also compared the aerodynamic polar and pitching moment coefficients variations of the Bombardier CRJ700 equipped with an adaptive versus a fixed winglet.

Free-Flight Aerodynamic Testing of the Skylon Space Plane

The determination of aerodynamic coefficients for complex high-speed vehicles still requires experimental measurement. This paper details the development of the free-flight measurement technique within the University of Oxford High Density Tunnel. In particular, a novel image processing technique is developed for calculating the position of the model from high-speed video. This study focuses on the measurement of high Reynolds number experimental aerodynamic data for a subscale model of the Skylon space plane of Reaction Engines. Testing was undertaken at a Mach 7 test condition replicating flight at an altitude of 63.5 km. Results for lift, drag, and pitching moment coefficients were obtained over a range of angles of attack. Lift coefficient was nearly linear over the range of angles of attack tested, and drag coefficient was parabolic in shape, but sensitive to model yaw. The vehicle was also shown to be statically unstable, a common characteristic of canard configuration vehicles.

THE IMPACT OF DIFFERENT OUTWARD AND INWARD PROTRUSION POSITIONS ON THE NACA 1410 AIRFOIL SECTION AT VARIOUS ANGLES OF ATTACK

The current work aims to increase the NACA 1410 airfoil's aerodynamic efficiency by altering its surface qualities for various angles of attack. The NACA 1410 airfoil's lower surface has semicircular outward and inward protrusions for a more advantageous profile. The lift and drag coefficients were calculated using CFD, at various attack angles, from -2º to 18º. An ANSYS Fluent Workbench model of the NACA 1410 airfoil was used to investigate flow characteristics at 3 x 105 Reynolds numbers. The semicircular protrusions caused turbulence, reducing pressure drag and increasing lift, delaying flow separation. The NACA1410 profile has protrusions facing outward, increasing the pitch moment coefficient. The inward protrusion was found to be more advantageous in the study of the effects of surface alterations on airfoils at various angles of attack.

Study on the Effects of Pedestrians on the Aerostatic Response of a Long-Span Pedestrian Suspension Bridge

According to a long-span pedestrian suspension bridge, the sectional models of the human-footbridge system were proposed, and then the force measurement tests were performed to study the effects of the pedestrian density (ρ), pedestrian permutation, and wind attack angle (α) on the drag force coefficient (CH), lift force coefficient (CV), and pitching moment coefficient (CM), respectively. So, it is found that: (1) with the increase of ρ, both CH and CV with α < −2° increase, while both CV with α ≥ −2° and CM with ρ ≠ 0.0 P/m2 decrease. (2) when ρ > 0.2 P/m2, there is a significant effect of the pedestrian permutations on CH and CM, while the effect of the pedestrian permutations on CV is small. Then, the static wind forces were calculated and applied to the pedestrian suspension bridge, and the effects of ρ and pedestrian permutations on the aerostatic response were studied. So, it is found that: 1) with the increase of ρ, the aerostatic response increases; 2) the effects of the pedestrian permutations with ρ ≤ 0.5 P/m2 on the aerostatic response can be ignored, while there are disadvantageous effects of the pedestrian permutations with ρ > 0.5 P/m2 and larger wind-blocking area on the aerostatic response.

Research on hydrodynamic characteristics of horizontal axis tidal turbine with rotation and pitching motion under free surface condition

To obtain the hydrodynamic loads of a floating horizontal-axis tidal turbine with rotation and pitching motion under the free surface condition, a numerical simulation method based on CFD is established. The inflow direction load, power and pitching moment coefficients at different pitch periods, pitch amplitudes and blade tip-immersion depths were analyzed. The results show that the instantaneous values of the inflow direction load, power and pitching moment coefficients have obvious periodic fluctuations, and the fluctuation amplitude increases with the increase of the pitch frequency and amplitude. On this basis, the damping and additional mass coefficients are obtained based on the least square method. The damping coefficient of inflow direction load and power coefficients fluctuates periodically, and the fluctuation period is equal to the pitch period. The damping coefficient of pitching moment coefficient also fluctuates periodically, and the fluctuation period is not only related to pitch period, but also related to the rotation period of the turbine. The research findings can provide relevant data for studying the coupling motion of floating tidal current energy device and control design of the output electricity.

Design and aerodynamic evaluation of a medium short takeoff and landing tactical transport aircraft

The present article deals with the conceptual design of a new medium short takeoff and landing tactical transport aircraft, which is intended to expand the institutional capabilities of the Colombian Air Force in terms of versatility and flexibility. An original design strategy was developed during the conceptual design, combining classical methodologies and high-fidelity computational fluid dynamics (CFD) simulations. This methodology allowed the aircraft to be assessed in a single design space, based on its design requirements, mission, and applicable airworthiness standards. Once obtained a baseline concept, the aerodynamic study focused on the flow around two types of wingtip devices: tip tanks and blended winglets. These devices were designed to optimize the performance capabilities of the aircraft, while keeping simple certification procedures. Wind tunnel experiments and CFD simulations were carried out to evaluate and select the best configuration. Lift, drag, and pitching moment coefficient charts, along with vorticity contours, are presented. Results showed that blended winglets have a significant potential for improving aircraft performance without severe structural weight penalties, allowing additional payload capabilities and/or increased range and fuel savings. Finally, the optimized aircraft is compared to major competitors in order to discuss and highlight its main advantages and feasibility for future production.

Analysis of the Magnus Moment Aerodynamic Characteristics of Rotating Missiles at High Altitudes

The Magnus moment characteristics of rotating missiles with Mach numbers of 1.3 and 1.5 at different altitudes and angles of attack were numerically simulated based on the transition SST model. It was found that the Magnus moment direction of the missiles changed with the increase of the angle of attack. At a low altitude, with the increase of the angle of attack, the Magnus moment direction changed from positive to negative; however, at high altitudes, with the increase of the angle of attack, the Magnus moment direction changed from positive to negative and then again to positive. The Magnus force direction did not change with the change of the altitude and the angle of attack at low angles of attack; however, it changed with altitude at an angle of attack of 30°. When the angle of attack was 20°, the interference of the tail fin to the lateral force of the missile body was different from that for other angles of attack, leading to an increase of the lateral force of the rear part of the missile body. With the increasing altitude, the position of the boundary layer with a larger thickness of the missile body moved forward, making the lateral force distribution of the missile body even. Consequently, Magnus moments generated by different boundary layer thicknesses at the front and rear of the missile body decreased and the Magnus moment generated by the tail fin became larger. As lateral force directions of the missile body and the tail were opposite, the Magnus moment direction changed noticeably. Under a high angle of attack, the Magnus moment direction of the missile body changed with the increasing altitude. The absolute value of the pitch moment coefficient of the missile body decreased with the increasing altitude.

Experimental Determination of the Impact of Floats on the Aerodynamic Characteristics of an OSA Model in Symmetric Flow

This paper presents the results of experimental determination of the impact of floats on the aerodynamic characteristics of an OSA model in symmetric flow. The studies have been performed in the low-speed wind tunnel at the Military University of Technology (MUT, Warsaw, Poland). The aircraft model was examined at the dynamic pressure q = 500 Pa in the following angle of attack range = -2828. The investigations have been performed for an aircraft model under plain configuration with floats and without floats. The influence of elevator and flap inclination on the aerodynamic characteristics of the model has also been analysed. The obtained values of aerodynamic drag coefficient, lift coefficient, pitching moment coefficient and lift-to-drag ratio have been presented in the form of tables and graphs. The studies performed demonstrated that the use of floats causes the increase of aerodynamic drag coefficient CD, maximum lift coefficient CLmax as well as critical angle of attack cr. The decrease of lift-to-drag ratio has also been observed. Its value in the case of the model with floats was up to 20% lower than in the model without floats. The studies also showed that the model equipped with floats had a lower longitudinal static stability margin than the model without floats.

Design of wind-turbine blades for improving aerodynamic performance using hybrid blades

The blade airfoil significantly influences the performance of wind turbine. This study designs a new hybrid blade airfoil (abbreviated as HBA) based on the previous airfoils (S809 and NACA 63215). The surface-flow modes, wake-flow characteristics, and aerodynamic performance of HBA were tested using various Reynolds numbers and angles of attack. The experimental methods involved (1) the smoke-wire visualization at low wind speeds, (2) the surface-oil flow visualization at high wind speeds, (3) the hot-wire anemometry, and (4) the six force–moment balancer. At blade stall, the lift coefficient of 2.12 for HBA is approximately twice that of 1.07 for S809 and NACA63215. The maximum lift–drag ratio of 6.11 for HBA is approximately twice those (3.63 and 3.13) of S809 and NACA 63215. Moreover, the HBA has a higher stall angle than those of the other two blades. The (pitch) moment coefficient of HBA is also higher than those of S809 and NACA 63215.

Trajectory and attitude deviations for internal store separation due to unsteady and quasi-steady test method

The deviations of trajectory and attitude angle for internal store separation are evaluated by two wind tunnel test methods. One is the Freedrop Test (FDT), which is known as unsteady and time-dependent method of scaled model. The other is the Captive Trajectory System (CTS) test, which is usually regarded as a quasi-steady and time-averaged test technology. The result shows that there is a streamwise adverse pressure gradient on the cavity resulting in a nose-up pitching moment coefficient (>0) acting on the store model. When the initial pitch angular velocity is 0, the store exits the shear-layer with a nose-up pitch attitude causing the store to climb back towards and collide with the aircraft. However, the store passes through the shear-layer into the freestream with a nose-down pitch, which causes a successful separation event when the initial pitch angular velocity < 0. The pitch angle obtained by unsteady test method is different from that by quasi-steady test method. The time-dependent test includes the aerodynamic force induced by pitch angular velocity whereas the time-averaged method (CTS) cannot reflect the effect of unsteady aerodynamic force. The deviation of vertical displacement is not obvious for FDT and CTS test since the store has an initial vertical velocity, which is dominant for the vertical displacement. This means that the highly unsteady flow can create unpredictability in aerodynamic pitching moment of the store, which can lead to the deviation of pitch angle for internal store separation.

Gradient based empirical cumulative distribution function approximation for robust aerodynamic design

A robust optimization approach based on the use of the conditional value at risk function is presented, together with an application to a robust transonic aerodynamic design problem of the central section of a Blended Wing-Body configuration. The conditional value at risk is estimated using an approach based on the empirical cumulative probability distribution function. The quantities of interest of the risk function are the aerodynamic characteristics of the airfoil, namely lift, drag, and pitching moment coefficients, computed solving the Reynolds-averaged Navier-Stokes equations with the open-source fluid-dynamic solver SU2. Conditional value at risk computation is costly, so techniques and methods for the reduction of the computational cost are introduced. In particular, the empirical cumulative distribution function is approximated with a first-order series expansion using efficiently calculated gradients from SU2 discrete adjoint solver.