中央空气流体动力学研究院

Direct numerical simulation (DNS) databases of developed turbulent channel flows are used for a priori and a posteriori testing of various formulations of wall-modeled large eddy simulation (WMLES). Average wall friction values and their root-mean-square deviations are compared with the exact data of the filtered DNS field; in addition, correlation coefficients between the exact friction field and that obtained using the wall function method are calculated. The equilibrium wall functions of Spalding, Werner and Wengle, Li et al. are considered, as well as various options for taking into account nonequilibrium effects in the approach of Li et al.: the contribution of the mean pressure gradient, the contribution of the total pressure gradient; additional inclusion of convective terms in the momentum equation are also considered. Conclusions are drawn on the applicability of wall functions when using instantaneous and time-averaged input data in LES simulations of wall-bounded flows.

The influence of preliminary cyclic deformation on the strength properties and the fracture kinetics of a unidirectional carbon fiber reinforced polymer composite material is studied. The effect of the preliminary cyclic loading amplitude on damage (investigated by X-ray computed tomography), acoustic emission parameters, and the characteristics of local deformed state (estimated by digital image correlation) is analyzed. Preliminary cyclic loading is found to cause an increase in the ultimate tensile strength and the fracture energy. A strain field investigation shows that the fracture of the specimen is accompanied by the formation of multiple defective regions characterized by a high local strain. Preliminary cyclic loading is found to bring about the nucleation of defects in the specimen volume, and they cause premature matrix cracking and the development of delamination at the fiber–matrix interface. This behavior is confirmed by the results of frequency–energy analysis of AE signals at various stages of fracture.

Aim . Solution of the Clausing equation describing rarefied gas flow in a circular pipe. Methodology . An approximate analytical solution of this equation is proposed, based on the method of self-similar interpolation. Results . The passage probabilities obtained in the study are compared with the results of known numerical solutions. Research implications . Calculating gas flow through channels of various geometries in vacuum systems is one of the most important problems in rarefied gas dynamics.

In-depth knowledge of the aerodynamic noise characteristics and the effectiveness of different noise reduction concepts for the high-lift device of a supersonic civil aircraft are very important for evaluating and reducing the noise of such aircraft. However, current experimental investigation in this field is particularly scarce and the aim of this paper is to remedy this knowledge gap. Detailed aeroacoustic measurements for a 37%-scale, semi-span supersonic wing model with high-lift devices were performed in the 5.5 m & times; 4 m aeroacoustic wind tunnel. Using a transverse microphone array in the flyover direction and a longitudinal microphone array in the sideline direction, an extensive set of acoustic data under different flow speeds (corresponding to Mach numbers of Ma = 0.09 to Ma = 0.22), geometric angles of attack (alpha = - 4 degrees to alpha = 25 degrees) and flap deflection angles (up to 30 degrees) was obtained. Moreover, two noise reduction concepts, i.e., structured porous flap edges and flap side-edge fences with different design parameters, were used to reduce the flap noise of the supersonic wing. Concurrently, a sixcomponent external balance was devoted to documenting the aerodynamic characteristics of the wing model and monitoring the aerodynamic efficiency of the two noise reduction concepts. Measured acoustic spectra showed that although the wind tunnel background noise is high and contaminates most of the spectra above 2 kHz, it still has enough signal-to-noise ratio (SNR) in the low to middle frequency bands so as not to affect the analysis of aerodynamic noise characteristics and conclusions of the noise reduction concepts. Moreover, the noise of the supersonic wing model generally increases in a wide frequency band with the increase of angle of attack and flap deflection angle, and Ma6 velocity scaling with frequency scaling produced good spectral collapse for the far-field noise. Noise directivity was not affected by the change of flow speed but was sensitive to both angle of attack and flap deflection angle. The tested structured porous flap edges have almost no noise reduction ability while the flap side-edge fences decrease the sound pressure level by up to 4 dB. Simultaneous aerodynamic force measurements indicated that the tested flap side-edge fences have a negligible impact on the aerodynamic performance of the supersonic wing model.

The results of measurements of the skin-friction coefficient, velocity profile, and wall static pressure fluctuations in an incompressible equilibrium turbulent boundary layer with zero pressure gradient, formed on the wall of a transonic wind tunnel at very high Reynolds numbers, are presented. The Reynolds number based on the momentum thickness ranged from 1.43× 10^4 to 2.51× 10^5 . The unsteady friction force was measured using a high-precision floating element, with an uncertainty of 1-1.3% . The boundary-layer velocity profile was obtained using a rake of total pressure probes. Wall static pressure fluctuations were measured using Kulite sensors. The mean skin-friction coefficient values are consistent with available experimental data in the literature, semi-empirical correlations, and DNS results. The study allowed refinement of the Kármán constant to k=0.391 , as well as adjustment of coefficients in known empirical and semi-empirical relationships relating the skin-friction coefficient to Reθ . In addition to the mean values, fluctuations of the skin-friction coefficient, spatially averaged over the floating-element surface, were obtained in the frequency range up to 250 Hz . A correlation was identified between fluctuations of the skin-friction coefficient and wall static pressure associated with large-scale turbulent structures in the boundary layer. The results may be used for validation of turbulence models and DNS data, as well as for estimating drag of trains, large aircraft, and ships.