Cruise Lift Coefficient Research Articles

DPW-7: Steady and Unsteady Computations of the Common Research Model at Different Reynolds Numbers

This article presents the numerical computations performed at ONERA for the Seventh AIAA Drag Prediction Workshop. By introducing Reynolds numbers up to 30 million closer to the flight conditions, greater lift levels beyond the design point, and time-accurate simulations, this new session has allowed the previous studies to be extended. The Common Research Model aircraft configuration has been considered in its academic wing-body version and calculated in this work with point-matched structured grids. The ONERA Cassiopee software as well as the elsA solver and the FFDπ far-field drag code have been used. The grid convergence study has shown larger pressure drag variations than what was obtained at the cruise lift coefficient, but increasing the Reynolds number seems to reduce this trend. Then, the angle-of-attack sweep study with the lift, drag, and moment polars has given the opportunity to assess different numerical settings such as the Spalart–Allmaras and shear stress transport turbulence models with the quadratic constitutive relation approach (QCR-2000) and to discuss the comparison between computational fluid dynamics results and wind-tunnel data. Concerning the Reynolds number increase, it has appeared that the main part of drag reduction comes from the friction () and viscous pressure drag () components. The prediction of pitching moment increments due to Reynolds number variations still needs to be significantly improved. Finally, for an angle of attack above 4.00 deg, by the use of unsteady Reynolds-averaged Navier–Stokes computations, an unsteady buffet phenomenon has been observed and analyzed.

Low-Reynolds-number airfoil design optimization using deep-learning-based tailored airfoil modes

Low-Reynolds-number high-lift airfoil design is critical to the performance of unmanned aerial vehicles (UAV). However, since laminar-to-turbulent transition dominates the aerodynamic performance of low-Reynolds-number airfoils and the transition position may exhibit an abrupt change even with a small geometric deformation, aerodynamic coefficient functions become discontinuous in this regime, which brings significant difficulties to the application of conventional aerodynamic design optimization methods. To efficiently perform low-Reynolds-number airfoil design, we present a tailored airfoil modal parameterization method, which reasonably defines the desired design space using deep-learning techniques. Coupled with surrogate-based optimization, the proposed method has shown to be effective and efficient in low-Reynolds-number high-lift airfoil design. It is found that it is necessary to consider laminar-to-turbulent transition and to perform multi-point optimization in practical low-Reynolds-number airfoil design. The maximal lift coefficient is an active constraint influencing the selection of the optimal cruise lift coefficient. The results show the complexity of low-Reynolds-number high-lift airfoil design and highlight the significance of the proposed method in the improvement of optimization efficiency.

Numerical analysis of propeller effects on wing aerodynamic: tip mounted and distributed propulsion

Abstract The purpose of this investigation is determinate the effects of propeller on wing aerodynamic, both for a propeller mounted in the middle of the wing, and for tip mounted propeller. Especially, it is investigated how a tip-mounted propeller can decrease wing induced drag, and how distributed propulsion can increase the high-lift aerodynamic. Analyses are carried out using a Virtual Disk Model on CFD software, showing a good agreement comparing numerical results with experimental data obtained by previous works. Wing tip engine with propeller, has been employed on a general aviation aircraft wing with an installed thrust to accomplish with cruise performance, reducing the induced drag. Distributed propeller engines on the wing allows improving of low speed performance, increasing the aircraft lift coefficient. Induced drag can be reduced of about 2-3% a low cruise lift coefficient, until 8-10% at relative high cruise lift coefficient. Maximum achievable lift coefficient could be increased of about 20-30% in clean configuration, and more than 50% in flapped configuration.

Instability analysis and drag coefficient prediction on a swept RAE2822 wing with constant lift coefficient

Swept wing is widely used in civil aircraft, whose airfoil is chosen, designed and optimized to increase the cruise speed and decrease the drag coefficient. The parameters of swept wing, such as sweep angle and angle of attack, are determined according to the cruise lift coefficient requirement, and the drag coefficient is expected to be predicted accurately, which involves the instability characteristics and transition position of the flow. The pressure coefficient of the RAE2822 wing with given constant lift coefficient is obtained by solving the three-dimensional Navier-Stokes equation numerically, and then the mean flow is calculated by solving the boundary layer (BL) equation with spectral method. The cross-flow instability characteristic of boundary layer of swept wing in the windward and leeward is analyzed by linear stability theory (LST), and the transition position is predicted by eN method. The drag coefficient is numerically predicted by introducing a laminar/turbulent indicator. A simple approach to calculate the lift coefficient of swept wing is proposed. It is found that there is a quantitative relationship between the angle of attack and sweep angle when the lift coefficient keeps constant; when the angle of attack is small, the flow on the leeward of the wing is stable. when the angle of attack is larger than 3°, the flow becomes unstable quickly; with the increase of sweep angle or angle of attack the disturbance on the windward becomes more unstable, leading to the moving forward of the transition position to the leading edge of the wing; the drag coefficient has two significant jumping growth due to the successive occurrence of transition in the windward and the leeward; the optimal range of sweep angle for civil aircraft is suggested.

Lift Distributions for Minimum Induced Drag with Generalized Bending Moment Constraints

The previous works of Prandtl, Jones, and Klein and Viswanathan addressed the problem of determining the lift distribution that minimizes induced drag for a given lift and specified bending moment. In these formulations, bending moment is considered to be a surrogate for wing weight. These classical methods require the bending constraints to be imposed at the same lift coefficient at which drag is minimized. In practice, however, it is commonly desired to minimize drag at a representative cruise lift coefficient while imposing the bending constraints at a limiting structural load condition, such as a maneuver lift coefficient. This paper presents an approach to extend the classical methods by allowing the bending constraints to be imposed at different lift coefficients than that at which induced drag is minimized. An example for a wing planform similar to that of a Boeing 737 shows that the penalty for optimizing induced drag at the maneuver lift coefficient as implied in the classical methods results in between a 1–10% increase in drag at cruise compared to the results from this new approach. It is expected that the new approach will enable the classical methods to be extended to practical applications in multidisciplinary wing design.

Optimization of planform and cruise conditions of a transport flying wing

The flying wing is a promising concept for the mid long-term commercial aviation. After the previously published conceptual design of a 300-seat class flying wing, the present article carries out a parametric analysis to optimize its planform and analyse the suitable cruise conditions to achieve the highest efficiency of such configuration. The figures of merit chosen for the optimization are the direct operating cost and the maximum take-off weight per passenger, for a specified constant range of 10 000 km. The design has to respect five relevant constraints: wingspan (limited to 80 m), cabin width, wing tip chord, number of passengers, and cruise lift coefficient. The optimum aircraft fulfilling all constraints cruises at 45 000–47 000 ft and M = 0.82, has an aspect ratio of 6.3 and taper ratio of 0.10, and carries about 280 passengers in three-class seating. This aircraft is about 20 per cent more efficient than conventional wide bodies of similar size, in terms of trip fuel.

Multidisciplinary Considerations in the Design of Wings and Wing Tip Devices

Conceptual wing design analysis methods are combined with numerical optimization to find minimum-drag wings subject to constraints on lift, weight, pitching moment, and stall speed. Tip extensions and winglets designed for minimum drag achieve similar performance, with the optimal solution depending on the ratio of the maneuver lift coefficient to the cruise lift coefficient. The results highlight the importance of accounting for the depth of the wing structural box in the weight model and including constraints on stall speed. For tailless aircraft, C-wings show a slight performance advantage over wings with winglets when longitudinal trim and stability constraints are considered. This performance advantage is more significant for span-constrained or low-sweep designs. Finally, to demonstrate other possible applications of the method, planar wings with active load alleviation are optimized, showing drag savings on the order of 15%.

Two-Dimensional Shape Optimization of Hypersonic Vehicles Considering Transonic Aerodynamic Performance

For the success of hypersonic vehicles, their shape must be optimized to achieve a high lift-to-drag ratio as well as a low aerodynamic heating rate in the hypersonic regime. In addition, the transonic lift-to-drag ratio must also be optimized to realize quick acceleration to the hypersonic cruise speed. The three-dimensional lift-to-drag ratio can be improved even by the two-dimensional section shape (i.e., airfoil) optimization in the region where the sweep back angle is small. Here, prior to three-dimensional shape optimization, a study is done to optimize airfoils of hypersonic vehicles based on these three parameters. At optimization, the hypersonic lift-to-drag ratio is maximized while the transonic lift-to-drag ratio and the aerodynamic heating rate are constrained. The optimum lift coefficient for hypersonic cruise at the maximum lift-to-drag ratio is investigated. The relation between the leading edge radius, which determines the aerodynamic heating rate, and the hypersonic lift-to-drag ratio is also investigated. Results show that to improve the hypersonic lift-to-drag ratio, the airfoil thickness around the leading edge should be small as long as an appropriate compromise with the transonic lift-to-drag ratio is achieved. Results also show that the optimum lift coefficient for hypersonic cruise is much lower than that for typical supersonic vehicles. Small cruise lift coefficient suggests that the wing loading of a hypersonic vehicle should be small. The leading edge radius should be determined by a compromise between the hypersonic lift-to-drag ratio and leading edge heating. Airfoil optimization can provide an appropriate initial guess of the three-dimensional optimum shape. By using an appropriate initial guess, the computation time of the three-dimensional shape optimization is expected to be reduced.

Design of a High-Lift, Thick Airfoil for Unmanned Aerial Vehicle Applications

The aerodynamic design of high-altitude unmanned aerial vehicles is driven by the rapidly decreasing air density at the upper boundaries of the atmosphere. A corresponding increase in wing area cannot provide a simple solution because of the additional weight and flexibility of the high-aspect-ratio wings. The excessive spanwise flexibility can be addressed by developing thicker airfoil sections that will increase the wing bending stiffness. Additional reduction in the expected wing size could be achieved by increasing the design cruise lift coefficient. Consequently, the objective of this study was to develop a 24% thick, two-element airfoil section capable of lift coefficients approaching two. Expected operational Reynolds number was estimated within the range of 0.5 to 1.0 x 10 6 . A secondary objective of this study was to experiment with the airfoil design-optimization procedure, which later could be automated.

Optimum cruise lift coefficient in initial design of jet aircraft

shows the average lift during the ramp-down motion is the dominant factor in the decline of the total average lift at high amax. In the analysis in Ref. 1 a dynamic lift augmentation of AL = 1.5 was assumed, and this resulted in an ALV with a near 20% improvement in straight-and-level range over the conventional baseline vehicle. In Fig. 3c, an augmentation of AL = 1.5 was achieved at the highest pitch rate of K = 0.2 and a0 = 0 deg and for both cases of K = 0.05 and 0.1 for starting angles of aQ = 10 deg. The asssumption of Ref. 1 concerning the existence of augmentation parameters near 1.5 and above would appear then to have some justification. Any benefits that might be gained from augmented lift must be weighed against the penalty levied by the increase in dynamic drag loading. Figure 4 shows the total time-average drag coefficients for each test motion. Figure 4 clearly shows that decreasing amax is advantageous from the standpoint of average drag reduction. From Fig. 3c at the pitch rates of K = 0.05 and 0.1 and starting angles of 10 deg, a value of amax = 35 deg results in nearly optimum lift augmentation with respective AL values of 1.5 and 1.63. The corresponding average drag coefficient is seen in Fig. 4 to be near 0.7, which by some standards is large. Notice, however, that the average drag decreases rapidly with decreasing amax, and for amax = 25 deg and pitch rates of K = 0.05 and 0.1, the average drag coefficient has dropped to 0.3 and 0.24, respectively. At the same time, the lift augmentation remains well above unity and, from Fig. 3c, has values of 1.38 and 1.34, respectively. Thus for the rate of K = 0.1, decreasing amax from 35 to 25 deg results in a drop in the average lift of 18% (though still maintaining significant lift augmentation), whereas the average drag decreases over 60%. In the present study the pitch rate for the ramp-up and ramp-down motions was the same. For a stopping angle of amax = 25 deg the data of Fig. 3a indicate that the average lift during ramp up generally increases with pitch rate, whereas in Fig. 3b the average lift during ramp down decreases with pitch rate. There may then be some advantage in ramping up at a high rate followed by ramping down at a lower rate. In the motions studied in Ref. 1 the rate during pull-up was lower than that for pitch-down. Maintaining acceptable drag loading may be a limiting condition for defining airfoil motions for the purpose of utilizing augmented lift.

Euler analysis of a High-Speed Civil Transport concept at Mach 3

A marching Euler solver, GEM3D, was used to predict the Mach 3 flowfield for the wing and body of a Highspeed Civil Transport (HSCT) concept. The analysis focused on a typical cruise lift coefficient of 0.1 at a = 3 deg. The Euler solution indicated that embedded shocks formed on the upper surface of the inboard wing panel and at the leading edge of the outboard wing panel caused by its supersonic leading-edge condition. According to a simple static-pressure criterion, the embedded wing upper-surface shocks were sufficiently strong to separate a turbulent boundary layer. Comparison of aerodynamic coefficients from the Euler solver with those from linear theory showed that the linear theory estimates of lift and drag were optimistic, which would lead to optimistic estimates of cruise range.