Rolling Moment Coefficient Research Articles

Wind Tunnel Tests of the Tu-154M Aircraft Aerodynamic Characteristics

Abstract Determination of possible manoeuvres to be performed by the aircraft requires knowledge of its aerodynamic characteristics including, in particular, characteristics of the aircraft at configuration with deflected control surfaces. In this article, the wind tunnel tests results of the model of passenger Tu-154M aircraft manufactured at the scale 1:40 are presented. The model was designed and manufactured by the Military University of Technology based on the Tu-154M aircraft geometry obtained by full-scale object scanning. The model mapped all aircraft control surfaces, along with the gaps between these surfaces and the main wing part. During the tests all the model’s control surface like, flaps, ailerons, spoilers, slots, rudder, elevator and tail plane were deflected at the same deflection angles range as they are used in the full scale aircraft. The aerodynamic characteristics of the tested Tu-154M aircraft model were measured by the 6-component internal balance. Based on the obtained measurements the aircraft model aerodynamic coefficients were calculated. In the article the basic aerodynamic characteristics of the tested Tu-154M aircraft model i.e. lift, drag coefficients as well as pitching, yawing and rolling moment coefficients versus model angles of attack and sideslip angles were presented. The tests were performed in the Institute of Aviation low speed wind tunnels T-1 of the 1.5 m diameter test section at the undisturbed velocity, V∞ = 40 m/s.

Physical simulations on wind loading characteristics of streamlined bridge decks under tornado-like vortices

Tornado risks for highly important long-span bridges in tornado-prone regions can not be neglected. Rigid-model wind pressure measurements on a streamlined bridge deck were conducted using a tornado vortex simulator, to clarify tornado-induced surface pressure distributions, aerodynamic load coefficients and total force coefficients. We focused on two main parameters: swirl ratio and horizontal distance from tornado center to deck. Obvious discrepancies were observed between tornado-induced wind loading and results from conventional boundary-layer wind tunnels. Strip theory was not applicable since pressure distributions vary for different sections of the deck along the bridge axis. The absolute values of mean pressure coefficients for the deck section near tornado center are largest among all tested sections along the bridge axis. The most unfavorable mean sectional drag force coefficients were found when the bridge model is located at the tornado core radius and largest mean sectional lift force coefficients at the tornado center. With increase in swirl ratio, magnitudes of mean pressure coefficients as well as mean and fluctuating sectional aerodynamic load coefficients become smaller. The unfavorable locations for fluctuating rolling moment coefficients are different from those for mean values, which indicates that the quasi-steady assumption becomes invalid for tornado-induced rolling moment coefficients. Total force coefficients over the entire deck were investigated to evaluate the non-uniform loading characteristics. The findings will be helpful for predicting tornado-induced responses and risks for highly important long-span bridges.

INFLUENCE OF THE AT "WINGLETS" TYPE ON THE LONGITUDINAL STATIC STABILITY OF ANGLE OF ATTACK OF THE AIRCRAFT

The effect of the aerodynamic AT winglets wingtips on the longitudinal static stability of the aircraft is investigated by the method of equations of a steady straight-line horizontal flight. The aerodynamic forces created by the upper and lower parts of the wingtip AT winglets are defined. Assuming that the vertical projections of the pressure centers of all parts of the wingtips intersect the transverse axis, the dive and kicking moments of these forces are determined. The aerodynamic forces created by all four parts of the wingtip AT winglets are determined and their pitch moments are calculated. The vector of the total aerodynamic force of the wingtips is represented in the form of components along the associated coordinate system. Equilibrium equations for the steady motion of an aircraft with wingtips of the AT winglets type in a horizontal flight are recorded. This method is used to calculate the expression for the longitudinal moment coefficient of an aircraft in the presence of aerodynamic wingtips. The forward and backward arrangements of the centers of pressure of the tips with respect to the vertical plane passing through the lateral coordinate axis are considered. The derivatives of the coefficients of the roll and yaw moment coefficients for the slip angle for the wing with the tips that enter the equation for the lateral oscillation of the aircraft are determined. The correspondence between the derivatives of the coefficients of the moments of roll and yaw for the wings without the tips and with the tips for the slip angle is established. Using this correspondence, from the known differential equation of the lateral oscillation of an airplane with a wing without a wingtip, the corresponding equation of lateral oscillation of the airplane is obtained for the aircraft for a wing with a wing with wingtips. The expression of the longitudinal moment and its coefficient for an aircraft taking into account the influence of aerodynamic wing tips is derived. With small changes in the angle of attack, the partial derivatives of the longitudinal moment coefficient with respect to the angle of attack and the coefficient of lift are calculated. The conditions for the longitudinal static stab

Aerodynamic moment characteristics of tandem-scheme aircraft

Aerodynamic interference between forward and back wings of tandem-scheme aircraft significantly affects its pitch and roll moments. The interference increases roll stability in a narrow range of sideslip angles; there is a kink on the dependence of roll moment coefficient versus sideslip angle (that is not observed for conventional-scheme aircraft). Directional stability is decreased by a dihedral angle of forward wings and winglets on them but is increased by the same factors for back wings. If back wings’ bending is significant, then aerodynamic interference may affect directional stability as well. The vortex system of tandem-wings at a sideslip angle was modeled incorrectly by the used CFD method (solving RANS), and further research is needed. The analytical and experimental methods show a good agreement concerning moment characteristics.

Calculation of the overturning wind speed of large road vehicles at exposed sites

High-sided vehicles are particularly vulnerable to high wind conditions and at sites that are regarded as vulnerable, a range of vehicle restrictions are imposed in high winds. These may include vehicle speed reductions or complete restrictions on the movement of different categories of vehicle at different wind gust speeds. This paper builds on earlier work that has been carried out and seeks to develop a simple but conservative method that can be used to specify vehicle restriction strategies. This is based on a collation of a wide range of data for aerodynamic rolling moment coefficients that allows a simple parameterisation to be developed. This is then used in an overturning model to develop a non-dimensional relationship between overturning gust speed and vehicle speed. The parameter used in the non-dimensionalisation is a characteristic wind speed that is a function of vehicle weight and geometry, and effectively specifies the vulnerability of the vehicle to overturning in high winds. Dimensional relationships between overturning gust velocities and vehicle velocities can thus be derived for different vehicle types and used to develop site-specific vehicle restriction methods.

Experimental Analysis of a Small-Scale Rotor at Various Inflow Angles

The performance characteristics of a rotor that is typically used for small unmanned aircraft were analyzed in a series of wind-tunnel experiments. Wind-tunnel measurements were conducted with the rotor at various inflow angles in order to investigate the effects on the rotor performance of partially or fully edgewise flow as they are typically encountered with small multirotor vehicles. Rotor tests were also performed under static and fully axial flow conditions in order to investigate the aerodynamic performance during hover as well as vertical climb and descent. The wind-tunnel data were corrected to account for the interference of wind-tunnel walls with the rotor wake and the blockage due to the presence of the rotor test stand in the wind-tunnel test section. The results are presented in terms of thrust, power, and roll moment coefficients under different rotor rotational speeds for a T-motor 18x6.1. Additionally, the measured thrust and power coefficients of Master Airscrew Electric 11x7 are compared with available propeller data under static and axial flow conditions for verification purposes. It is shown that the rotor performance characteristics are strongly affected by the freestream advance ratio and the freestream inflow angles. For example, at inflow angles that are typical for multirotor vehicles between about 15° and 0° with respect to the rotor disc, thrust coefficients stay constant or grow with increasing advance ratio, whereas power coefficients remain relatively constant with changing advance ratio.

Fluctuations of an airplane with aerodynamic wingtip «At winglets»

By the method of equations of steady rectangular horizontal flight the effect of the aerodynamic wingtips AT winglets on the lateral oscillating stability of the aircraft is investigated. This method calculates the expressions for the coefficients of the roll and yaw moments for a wing with wingtips, which are used here to obtain an approximate equation for the lateral oscillatory motion of the aircraft. The forward and backward arrangements of the centers of pressure of the tips with respect to the vertical plane passing through the lateral coordinate axis are considered. The derivatives of the coefficients of the roll and yaw moment coefficients for the slip angle for the wing with the tips that enter the equation for the lateral oscillation of the aircraft are determined. The correspondence between the derivatives of the coefficients of the moments of roll and yaw for the wings without the tips and with the tips for the slip angle is established. Using this correspondence, from the known differential equation of the lateral oscillation of an aircraft with a wing without an wingtip, the corresponding equation of lateral oscillation of the airplane is obtained for the aircraft for aircraft with a wing with wingtips. A study is made of the solution of this equation in terms of stability, depwingtip on the ratio of the attenuation coefficient and the coefficient of dynamic stability of the aircraft in yaw . The study showed that for a stable lateral oscillation of an airplane, the numbers and must be negative and, in addition, still should be less than a negative number, i.e . It is shown that, in the case of steady lateral oscillations, the presence of wing tips leads to an increase in the oscillation frequency and amplitude decay factor as compared to the wing without the wingtips.

The Impact of Air Fences Geometry on Air Flow around an ICE3 High Speed Train on a Double Line Railway Track with Exposure to Crosswinds

Reduction in weight adjoined with the increase in the railway vehicle speed of travel added to the deteriorating effects of the crosswinds on the running behavior of high speed trains. During the past decade, many researchers have concentrated on examining the aerodynamic force and moment coefficients for the trains. Varieties of studies regarding the effects of crosswinds on the trains are accomplished. However, the need to restrain strong winds from disturbing trains running safety is not completed. This research is concerned with finding a proper solution for attenuating the worrying effects of the winds that hit the trains. Installation of air fences on the sides of the railway tracks is investigated. To serve the purpose, a variety of air fences with different heights, with and without the edges on top of the fences, at a variety of the edge lengths and angles are studied. The study covers double routed railway track while the air fences are installed on either side of the track. The train can be on the leeward or windward line. The problem solving is based on the Lattice-Boltzmann method. This research pioneers in using this method for the said purpose. It is found that by inserting the fences and increasing their heights for up to 1m, the drag forces decrease to 40 percent and the rolling moment coefficients decrease to 15 percent. The presence of the edge can also decrease the drag force for about 55 to 120 percent and decrease the rolling moment coefficients for about 30 to 115 percent in some cases. Variations in percentages of reduction are due to the different angles and the lengths of the edges.

Comparative analysis of the effect of different nose lengths on train aerodynamic performance under crosswind

This study investigated the aerodynamic performances of four trains with different nose lengths (4, 7, 9 and 12 m) under strong crosswind using the detached eddy simulation (DES) method. The variations in the aerodynamic force coefficients with different nose lengths were analyzed. The pressure distribution on the train surface, vortex development around the train, and velocity field variation around the train with increases in the nose length were compared and discussed. The results indicated that in a strong wind environment, the aerodynamic drag coefficient was largest for the tail car, whereas the side force coefficient, lift coefficient and roll moment coefficient were largest for the head car. When the nose length of the train increased from 4 m to 12 m, the total drag coefficient of the train decreased by 19.0% and the side force, lift and roll moment coefficient decreased by 10.6%, 21.7% and 7.3%, respectively. In the horizontal section of the train head part and tail part, the largest pressure coefficient decreased in a logarithmic manner with increases in the nose length. The nose length significantly affects the pressure coefficient on the windward side of the head car and the leeward side of the tail car. With an increase in the nose length, on the leeward side of the train, the shedding length and influence width range of vortex were reduced; the strength of the spiral shedding and interaction effect of two vortices in the rear nose weakened, and their distinction was more notable, meanwhile, the wake impact ranges in the vertical and longitudinal directions decreased.

Main Rotor Trimming Using CFD Method in Forward Flight

In this paper a CFD trimming method was proposed and compared with wind tunnel experiment and blade element method. NASA’s generic ROBIN helicopter model was adopted for transient simulations to get the final main rotor trimming condition. Totally three steps were applied to CFD method, one being no cyclic pitch motion, one being pure longitudinal cyclic pitch motion and the other one being pure lateral cyclic pitch motion. At the same time, a simple linear equation system between the roll and pitching moment was adopted to get the final longitudinal and lateral cyclic pitch angles for the main rotor through these three steps. An overset grid approach was used where the volume around each blade was modeled in an individual overset grid region. The rotor rotation was resolved with 3 degree per time-step. Turbulence was modeled with the well known SST K-omega model with 2nd order convection. The helicopter was in straight forward flight with an advance ratio of μ=0.151. Three sources of stick angles, which are also calling rotor trimming angles, were shown and compared with each other. And the corresponding results were also plotted with type of history plot in CFD condition. In the simulations the results became quasi periodic after about 1.5 rotations and 4 rotor rotations were simulated for each case. The pitch moment coefficient and roll moment coefficient were all trimmed to zero by CFD trimming method while moments were not be removed thoroughly in other two sources condition. So, it is concluded that CFD trimming method has an ability to trim helicopter main rotor in forward flight.

Numerical simulation on rolling characteristics of canard-controlled rockets with a free-spinning tail

Rolling characteristics of the canard-controlled rocket with a free-spinning tail are researched based on 3-dimensional Navier–Stokes (N–S) equations. The slide mesh technology of computational fluid dynamics is used to numerically simulate the flow field when tails rotate relative to the rocket body and research the varying pattern of roll moment coefficients of the whole rocket, tail, and canard with Mach number. The comparison between the computation results and a part of experimental data shows that the simulation method is accurate. The convergence criterion during the numerical simulation is put forward; the induced rotation speed of the free-spinning tail and the roll moment coefficient of the rocket under this rotation in actual flight when the canard deflects by 10[Formula: see text] for roll control are obtained and the reason for the free-spinning tail being able to eliminate roll coupling is analyzed. The research provides a reference for the configuration design of canard-controlled rockets with a free-spinning tail and the numerical simulation of their aerodynamic characteristics.

Numerical Investigation of Aerodynamic Characteristics of High Speed Train

In this work, initially the effect of nose shape on the drag characteristics of a high speed train is studied. Then the influence of cross winds on the aerodynamics and hence the stability of such modern high speed trains is analyzed. CFD analysis was conducted using STAR-CCM+ on trains with different features and important aerodynamic coefficients such as the drag, side force and rolling moment coefficients have been calculated for yaw angles of crosswinds ranging from 0° to 90°. The results show that the modification on train nose shape can reduce the drag up to more than 50%. It was also found that, bogie faring only reduces small percentage of drag but significantly contributed to higher rolling moment and side force coefficient hence induced train instability.

Fluid-structure interaction of a rolling restrained body of revolution at high angles of attack

The current work investigates numerically rolling instabilities of a free-to-roll slender rigid-body of revolution placed in a wind tunnel at a high angle of attack. The resistance to the roll moment is represented by a linear torsion spring and equivalent linear damping representing friction in the bearings of a simulated wind tunnel model. The body is subjected to a three-dimensional, compressible, laminar flow. The full Navier-Stokes equations are solved using the second-order implicit finite difference Beam-Warming scheme, adapted to a curvilinear coordinate system, whereas the coupled structural second order equation of motion for roll is solved by a fourth-order Runge-Kutta method. The body consists of a 3.5-diameter tangent ogive forebody with a 7.0-diameter long cylindrical afterbody extending aft of the nose-body junction to x/D = 10.5. We describe in detail the investigation of three angles of attack 20°, 40°, and 65°, at a Reynolds number of 30 000 (based on body diameter) and a Mach number of 0.2. Three distinct configurations are investigated as follows: a fixed body, a free-to-roll body with a weak torsion spring, and a free-to-roll body with a strong torsion spring. For each angle of attack the free-to-roll configuration portrays a distinct and different behavior pattern, including bi-stable limit-cycle oscillations. The bifurcation structure incorporates both large and small amplitude periodic roll oscillations where the latter lose their periodicity with increasing stiffness of the restraining spring culminating with distinct quasiperiodic oscillations. We note that removal of an applied upstream disturbance for a restrained body does not change the magnitude or complexity of the oscillations or of the flow patterns along the body. Depending on structure characteristics and flow conditions even a small rolling moment coefficient at the relatively low angle of attack of 20° may lead to large amplitude resonant roll oscillations.

Main helicopter rotor trimming using computational fluid dynamics method in forward flight

In this paper, a computational fluid dynamics trimming method is proposed and compared with wind tunnel experiment and the blade element method. The NASA’s generic ROBIN helicopter model is adopted for transient simulations to obtain the final main rotor trimming conditions. Totally three steps were applied to the computational fluid dynamics method. The first step is associated with no cyclic pitch motion, the second is regarding pure longitudinal cyclic pitch motion and the last is concerning with pure lateral cyclic pitch motion. At the same time, a simple linear equation system between the roll and pitching moment was established to get the final longitudinal and lateral cyclic pitch angles for the main rotor through the above three steps. An overset grid approach was used where the volume around each blade was modeled in an individual overset grid region. The rotor rotation was resolved with three degrees per time-step. Turbulence was modeled with the well-known SST K-omega model with second-order convection. The helicopter was in straight forward flight with an advance ratio of [Formula: see text]. Three sources of stick angles, which are also called rotor trimming angles, were shown and compared with each other. And the corresponding results were also plotted with a type of history plot in the computational fluid dynamics condition. In the simulations, the results became quasi periodic after about 1.5 rotations and four rotor rotations were simulated for each case. The pitch moment coefficient and roll moment coefficient were all trimmed to about zero by the computational fluid dynamics trimming method while moments were not removed thoroughly in the other two source conditions.

Comparison between steady and moving railway vehicles subjected to crosswind by CFD analysis

CFD simulations are used to investigate the effect of the relative motion between train and infrastructure scenario in order to analyze the differences which occur in wind tunnel experience between static and moving vehicles. After an initial validation against experimental data, the numerical model is then used to study the effects of the relative motion between train and infrastructure model (Single Track with Ballast and Rail, i.e. STBR). The variation, in terms of aerodynamic coefficients obtained with moving and still model simulations, is analyzed: the lateral force and the rolling moment coefficients are lower with the stationary model of about 5% and the differences are of about 12% for the vertical force coefficient. The corresponding variation in terms of Characteristic Wind Curves, representing the limiting conditions for train overturning is in the order of 1.5% for wind perpendicular to the train direction. In conclusion, even if static tests are not conservative, the differences in terms of CWC are significantly low in the STBR scenario and these results support adoption of still model tests on STBR scenario as representative of train aerodynamics.

Study on Rolling Characteristics of the Projectile with Wide-Angle Oblique Empennages

Due to requests on high rotary velocity of novel smart empennage-stable projectiles, the rolling characteristics under wide-angle oblique angles are studied. Since the wind tunnel tests performed verify numerical simulation, so that the latter method can be applied to study the rolling characteristics widely combining theoretical models. In the theoretical part, the rolling dynamics equations are established considering the span, taper ratio and oblique angle of the empennages, and are further solved combing ballistic equations. For the simulation, the rolling moment coefficients under various rotary velocities are solved based on rotating coordinate system methods, so that the balance rotary velocity can be obtained using interpolation. The results indicate that shorter span, higher taper ratio and especially larger oblique angle can bring higher projectile rotary velocity; the balance rotary velocity is approximately linear to the oblique angle in a certain range.

Effect of sideslip angle on the aerodynamic characteristics of a following aircraft in close formation flight

The effect of sideslip angle on the aerodynamic characteristics of a following aircraft in formation flight is investigated by experiment. Measured data from subsonic wind-tunnel testing are obtained by changing the magnitude of the sideslip angle and the relative distances between the two-5% scaled small sized jet aircraft models. The variations of aerodynamic forces and moments of a following aircraft model are measured at 49 locations on the cross-section area behind a leading aircraft. Results show the considerable changes of the aerodynamic forces and moments of the following aircraft compared to those of a single aircraft alone. The effect of the sideslip on the aircraft in formation flight is a very complex function of relative distances between two aircraft, and has a significant effect on the lateral/ directional stability of the following aircraft. Among the changes of the aerodynamic coefficients, the changes of the rolling moment coefficients are the largest. It is believed that the formation flight itself can be a very dangerous to the safety flight of the aircraft.

Windbreaks for railway lines: Wind tunnel experimental tests

A number of tests were carried out in the Politecnico di Milano wind tunnel to study the properties of different windbreak barriers for high-speed railway lines. A possible problem with the wind tunnel testing of these devices is the need to create wide scenarios (long barriers) and achieve high Reynolds number values in order to avoid scaling problems. In this study, two experimental campaigns were performed. In the first stage, the Reynolds number sensitivity was checked through specific tests in a high-speed test section (Remax = 7 × 105): it was found that, in the presence of barriers, the rolling moment coefficient is independent of the Reynolds number. A second experimental campaign was then carried out in a low-speed test section (Remax = 1.3 × 105) where a very long scenario was reproduced (150 m at real scale): barriers of different types, heights and porosities were tested. To compare them, forces and pressures on the vehicle model as well as forces on the barrier were measured.

Aerodynamic control of NACA 0021 airfoil model with spark discharge plasma synthetic jets

Spark discharge plasma synthetic jets (SPJs) have been used for the active flow control study on an NACA 0021 straight-wing model in a wind tunnel. The model forces and moments were measured using a six-component sting balance at a 20 m/s wind speed. The aim was to explore the SPJ’s effect on airfoil aerodynamic by examining SPJ generators’ position along the chordwise and the jet flow direction about the chord. Near the wing leading edge, two SPJ generators raised the stall angle by 2° and increased the maximum lift coefficient by 9%. The drag coefficient was decreased by 33.1%, and the lift-drag ratio was increased by 104.2% at an angle of attack above 16°. The rolling-moment coefficient was modified by 0.002, and the yawing-moment coefficient was changed by 0.0007 at angles of attack in the range of 0°–16°. The results showed that SPJs can control wing aerodynamic forces at a high angle of attack and moments at a low angle of attack.

Crosswind effects on the stability of a model passenger train—A comparison of static and moving experiments

This paper explores the results obtained from an innovative physical model study which examined wind induced forces and pressures on a 1:25 scale model of a Class 390 Pendolino at a 30° yaw angle. For the first time, the work considers in detail the differences between moving model experiments and static experiments. Differences between the static and moving experiments are observed in the pressure distribution on the nose region of the train, however over the rest of the train the differences between the two sets of experiments are within the experimental uncertainty. The overall side, lift and rolling moment coefficients acting on the train are also shown to agree. This paper provides the scientific underpinning embedded within the current industrial guidelines and once and for all, demonstrates that in terms of the overall mean aerodynamic side and lift forces and rolling moment coefficients, static experiments are sufficient.