Journal of Aerospace Engineering

Many studies have focused on the application and mechanism of coflow jet (CFJ) flow control technique in incompressible flow. However, the influence of CFJ parameters in subsonic flow is still uncertain. Five major CFJ airfoil parameters are investigated for their influence and mechanism on lift enhancement, flow separation control, and aerodynamic efficiency at Mach numbers 0.3 and 0.5 in this study. Two optimized CFJ airfoils are then designed to achieve better overall performance, and are compared with a baseline CFJ airfoil. An improved computational model using an actuator disk boundary is applied to simplify the iteration process in numerical simulation. The results show that the interaction between the jet flow and supersonic region on the upper surface is the prominent factor for CFJ airfoils in subsonic flow, and the proper injection location should be downstream of the normal shock wave to prevent interaction, increase maximum lift, and delay stall. Moderate injection orifice size and proper jet momentum coefficient are recommended to balance the energy consumption and aerodynamic performance at high angles of attack. A control strategy that varies the jet momentum coefficient for different angles may achieve high aerodynamic efficiency as much as possible. A relatively front suction location can suppress flow separation more efficiently, and larger suction orifice is better for reducing energy consumption. The optimized CFJ airfoils have much better overall performance than the baseline CFJ airfoil. The enhancement of maximum lift increases to more than 30% and the stall is delayed by 3° with high jet momentum coefficient. The energy consumption is largely reduced, and the maximum corrected lift-to-drag ratio increases by 61% and 28% at Mach numbers 0.3 and 0.5, respectively. Also, the optimized CFJ airfoils can provide higher lift than the baseline airfoil with the same aerodynamic efficiency.

The mobile lunar lander (MLL), a novel lander configuration endowed with both landing and moving capabilities, promises to serve as a mobile habitat for future lunar research station construction. This paper studies the landing–moving integrated gear (LMIG) of the MLL that includes 10 design parameters, establishes the dynamic landing model, designs the performance evaluation indexes, analyzes the relationship between the design parameters and performance indexes, and proposes a multiparameter stepwise optimization approach based on capability priority grouping. The results indicate that the established dynamic landing model agrees well with the simulation results, with a maximum error of 3.07% for the descent distance. The parameters that significantly affect the performance indexes include the angle between the landing leg and the horizontal ground, the length of the primary strut, and the stroke of the buffer. The optimization approach prioritizes the different capabilities by determining the work sequence of MLL and optimizes the design parameters by grouping them based on the sensitivity of design parameters to performance indexes using the nondominated sorting genetic algorithm. This approach reduces the dimension of the multiparameter optimization issue and yields the optimal configuration of the LMIG. Additionally, the optimization results show that all performance indexes have been improved, with the obstacle crossing index reaching the greatest performance improvement of 12.45%, and the proposed analysis and optimization approach can also benefit other mechanisms with multiple capabilities and parameters.

This paper presents an in-depth investigation into the near-field pressure and far-field acoustic characteristics of a National Advisory Committee for Aeronautics (NACA) 16-506 airfoil across the prestall, stall, and poststall flow regimes at a Reynolds number of 270,000. The paper specifically focuses on examining the effect of the airfoil’s stalling behavior on its self-noise. The NACA 16-506 airfoil was tested in the aeroacoustic wind tunnel facility at the University of Bristol. Remote sensors were employed to record static pressure and unsteady pressure fluctuation data on the airfoil surface. Additionally, a 78-microphone beamforming array was used to measure the far-field sound, and acoustic spectra subsequently were extracted using a delay-and-sum beamforming technique. The NACA 16-506 airfoil was found to stall by the well-established thin-airfoil mechanism, characterized by the development and growth of a leading-edge separation bubble over a range of angles of attack before bursting and leading to full-chord separation. It was observed that the near-field unsteady pressure field began to change significantly at the onset of the leading-edge separation bubble, whereas the near-field steady pressure field, and consequently the aerodynamic performance, only showed significant changes when the separation bubble burst at a higher angle of attack. It was found that the far-field acoustics changed in concert with the near-field unsteady pressure field, rather than with the aerodynamic performance of the airfoil. In essence, the airfoil self-noise was found to increase in the manner typically associated with stall at an angle of attack significantly earlier than the aerodynamic stall angle. A comparison of the measured acoustic spectra and the trailing-edge noise model of Amiet with two forms of the Brooks, Pope, and Marcolini (BPM) noise model revealed that better noise prediction was achieved when the stall switch within the model was set to the angle of attack corresponding to the onset of the leading-edge separation bubble, rather than to the later aerodynamic stall angle. This simple modification to the BPM model is useful for any airfoil known to stall via a thin-airfoil mechanism.

In the field of aerodynamic noise, quick and correct source localization is of interest. The recent developing machine learning–based source localization methods are known for high-resolution and high calculation speed. However, the assumption of several point sources hinders machine learning methods in practical aeroacoustics experiments, in which a large number of sound sources are commonly distributed. In this paper, a coarse grid–based convolutional neural network (CG-CNN) method is proposed to predict the source strength at any position within the region of the scanning grid in a grid-independent way, which is effective for handling distributed sources in a fine grid. Instead of learning and predicting samples of point sources in a grid-free way or on the same fine grid in a grid-based way, the proposed method trains the model with point sources on a coarse grid and predicts the strength of these sources at any position. In the training process, the convolutional neural network model with a source cross-power matrix as inputs learns samples of sources on a coarse grid with low computational cost. In the predicting process, given that the source could be located at any position on the translated coarse grid, the CG-CNN method predicts the source strength on a translated grid point by directly changing the input of model according to the location of the grid. Simulation results prove that the method localizes point sources and line sources better than traditional beamforming methods in terms of accuracy and dynamic ranges. The CG-CNN method was applied in a wind tunnel experiment with a high-lift device with a serrated slat, and the distinct locations of sources are identified correctly. In general, the proposed method has high efficiency in learning from sources on a coarse grid and predicting sources at any position, which is helpful for distributed sources in aerodynamic noise investigations.

Space debris brings severe threats to the safety of spacecraft in low orbit. As a typical satellite system with high accuracy in low Earth orbit, the impact of space debris on TianQin-2 (TQ-2) is likely to result in the divergence of the control system, which will affect the scientific exploration mission. In this paper, the robustness of long-term missions for TQ-2 in a debris environment in low orbit is studied. Firstly, the models of the attitude and orbit control system for the double satellite formation and test mass of TQ-2 are established. Secondly, probability and momentum models of space debris that impact the TQ-2 is established, and the distribution of space debris and the probability density of time for two independent collisions are obtained according to the relevant conditions. Finally, through Monte Carlo simulation and statistics, the critical linear and angular momentum that causes the control system to diverge are analyzed and calculated. The changes in orbit and attitude for the control system in the critical state are simulated. During the 3-year mission period, the probability of the TQ-2’s control system exiting science mode or diverging due to debris impact was studied, which provides a reference for the normal manner and management of the TQ-2 in orbit.

This article presents an efficient frequency fusion method by virtual acquisition of multifrequency guided wave velocity data for robust and accurate localization of multiple damages in plate-like structures. Lamb waves are actuated by applying voltage excitation to piezoelectric patch transducers affixed on the plate, and the velocity response is measured using the noncontact scanning laser Doppler vibrometer (SLDV). The results show that the usual root mean square (RMS) and weighted RMS maps of the velocity field measured using a single narrowband pulse excitation of a given central frequency may not accurately localize multiple damages. To overcome this challenge, we propose a fusion method in the form of the product of normalized reciprocal root mean square ($r\mathrm{RMS}$) maps at multiple narrowband excitation frequencies for combining the measurement data from the different excitation frequencies. However, SLDV measurements at multiple narrowband frequencies would be tedious, time-consuming, and expensive. This difficulty is eliminated by virtually computing the velocity fields at various narrowband frequencies from a single physical measurement using broadband excitation. The efficacy of the proposed method is verified through the experimental investigation on an aluminum plate with multiple damages of different shapes and orientations for two different damage scenarios. The method could identify all damages accurately and clearly through sharp peaks in the $r\mathrm{RMS}$ amplitude at the damage locations without any accompanying ripples near them. On the other hand, the RMS and weighted RMS maps do not perform as well even after applying fusion of multiple frequencies.