Attenuation of boundary-layer instabilities for natural laminar flow design on supersonic highly swept wings

To meet the challenge of drag reduction for next-generation supersonic transport aircraft,increasing attention has been focused on Natural Laminar Flow(NLF)technology.However,the highly swept wings and high-Reynolds-number conditions of such aircraft dramatically amplify Crossflow(CF)instabilities inside boundary layers,making it difficult to maintain a large laminar flow region.To explore novel NLF designs on supersonic wings,this article investigates the mechanisms underlying the attenuation of Tollmien-Schlichting(TS)and CF instabilities by modifying pressure distributions.The evolution of TS and CF instabilities are evaluated under typical pressure distributions with different leading-edge flow acceleration region lengths,pressure coefficient slopes and pressure coefficient deviations.The results show that shortening the leading-edge flow acceleration region and using a flat pressure distribution are favorable for suppressing CF instabilities,and keeping a balance of disturbance growth between positive and negative wave angles is favorable for attenuating TS instabilities.Based on the uncovered mechanisms,a strategy of supersonic NLF design is proposed.Examination of the proposed strategy at a 60°sweep angle and Ma=2 presents potential to exceed the conventional NLF limit and achieve a transition Reynolds number of 17.6million,which can provide guidance for NLF design on supersonic highly swept wings.

Deep learning for inverse design of low-boom supersonic configurations

Mitigating the sonic boom to an acceptable stage is crucial for the next generation of supersonic transports.The primary way to suppress sonic booms is to develop a low sonic boom aerodynamic shape design.This paper proposes an inverse design approach to optimize the near-field signature of an aircraft,making it close to the shaped ideal ground signature after propagation in the atmosphere.By introducing the Deep Neural Network(DNN)model for the first time,a predicted input of Augmented Burgers equation is inversely achieved.By the K-fold cross-validation method,the pre-dicted ground signature closest to the target ground signature is obtained.Then,the corresponding equivalent area distribution is calculated using the classical Whitham’s F-function theory from the optimal near-field signature.The inversion method is vali-dated using the classic example of the C608 vehicle provided by the Third Sonic Boom Prediction Workshop(SBPW-3).The results show that the design ground signature is consistent with the target signature.The equivalent area distribution of the design result is smoother than the baseline distribution,and it shrinks significantly in the rear section.Finally,the robustness of this method is verified through the inverse design of sonic boom for the non-physical ground signature target.

Far-field sonic boom prediction considering atmospheric turbulence effects: An improved approach

Accurate prediction of sonic boom is one of key challenges for the design of a low-boom supersonic aircraft. For most of available far-field prediction methods, the effect of atmospheric turbulence appearing in the planetary boundary layer cannot be considered, which results in remarkable inaccuracy of predicting ground-level sonic boom waveform. Although some efforts have been made to overcome the shortcoming, the turbulence effects are not yet well described so far. This article proposes an improved method by extending the two-dimensional Heterogeneous One-Way Approximation for the Resolution of Diffraction(HOWARD) equation to account for the axial and transverse convections of wind fluctuation as well as the effect of temperature fluctuation. The proposed method is validated by comparing the predictions with the flight-test data of JAXA D-SEND#1 LBM, which shows that the result of the proposed method is in better agreement with the flight-test data than that of the method without considering atmospheric turbulence effects.Then, distortion mechanism of sonic boom waveforms caused by atmospheric turbulence is analyzed by using the proposed method. It is indicated that the effect of turbulent convection makes uniform sonic-boom wavefronts irregular, which creates the condition of diffraction effect to perturb waveforms. Finally, the proposed method is applied to investigate the behavior of two types of waveforms given by the sonic boom minimization theory. Results show that a far-field waveform with a weaker initial shock is more beneficial for low-boom design of a supersonic aircraft.

Effect of longitudinal lift distribution on sonic boom of a canard-wing-stabilator-body configuration

After the last flight of the Concorde in 2003,sonic boom has been one of the obstacles to the return of a supersonic transport aircraft to service.To reduce the sonic boom intensity to an acceptable level,it is of great significance to study the effect of lift distribution on far-field sonic boom,since lift is one of the most important contributors to an intense sonic boom.Existing studies on the longitudinal lift distribution used low-fidelity methods,such as Whitham theory,and in turn,only preliminary conclusions were obtained,such as that extending the lift distribution can reduce sonic boom.This paper uses a newly developed high-fidelity prediction method to quantitatively study the effect of longitudinal lift distribution on the sonic boom of a Canard-Wing-Stabilator-Body(CWSB)configuration.This high-fidelity prediction method combines near-feld CFD simulation with far-field propagation by solving the augmented Burgers equation.A multipole analysis method is employed for the extraction of near-field waveform in order to reduce computational cost.Seven configurations with the same total lift but different distributions are studied,and the quantitative relationship between the longitudinal lift distribution and far-field sonic boom intensity is investigated.It is observed that a small lift generated by the stabilator can prevent aft-stabilator and aft-fuselage shocks from merging,while the balanced lift generated by the canard and wing can effectively keep the corresponding shocks further apart,which is beneficial for reducing both the on-track and off-track sonic boom.In turn,the acoustic level perceived at the ground can be reduced by 5.9 PLdB on-track and 5.4 PLdB off-track,on average.

Modern problems of aircraft aerodynamics

The article represents the discussion of several separate directions of investigations,which are performed by TsAGI flight vehicles aerodynamics specialists at the time.There are some major trends of classical layout of route aircraft and also peculiarities of some prospective flight vehicles.Also there are some hypersonic vehicles aerodynamics questions examined along with problems of creation of civil supersonic transport aircraft.There is a description given for well-known and some newer methods of flow control for drag reduction.