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The flow across the blade tip clearance in turbomachinery is simplified as pressure-driven tip leakage flow (TLF) by isolating it from the mainstream. Based on schlieren visualization and numerical simulations, several common features of TLF are achieved. Consequently, a diffusion model is proposed to evaluate the mean flow and shock motions within the clearance. It takes into consideration the effects of relative wall motion by superposing a fully developed Couette flow. In addition, the over-tip shock waves are treated as repeated sawtooth wave to model the propagation. This approach enables quick and accurate evaluations of the meanflow and shock motions under configurations of stationery and moving casing wall. Given the flow variables at boundaries of the shock region, the meanflow and the evolution of the over-tip shock waves can be achieved instantly with an error less than 2%. Another advantage of this model is it can be non-intrusive. Hence, the challenges, arising from spatial constraints in direct measuring of TLF within the clearance, are surmounted. This is beneficial for locating the tip flow loss and the shock-induced heat load. Two flow mechanisms are unveiled from the predictions: (1) The strongest shock–boundary interaction accompanied by strong momentum exchange occurs above the separation bubble. (2) The oscillation of over-tip shock waves is self-sustained by a feedback loop formed by the pressure-side vortex shedding, shock generation, and shock–boundary interactions. [ABSTRACT FROM AUTHOR]

Aiming at the key scientific problems of strengthening cooling and heat dissipation of turbine blades, a new type of corrugated channel cooling structure was proposed in this work. Refined numerical simulation was carried out in six different corrugated channels, and the physical mechanism of flow and heat transfer was analyzed in detail. The results show that the corrugated channel has smaller flow resistance than the ribbed channel. Among the corrugated channels, the heat transfer effects of sinusoidal, triangular, and sawtooth2 corrugated channels are stronger than rib corrugated channel at the high Reynolds number, and these effects are distributed evenly. Within the six kinds of corrugated channels, the sinusoidal corrugated channel has the best comprehensive heat transfer effect. The blades with sinusoidal corrugated channels have better cooling effect due to the significant increase in heat transfer coefficient on the inner channel surface, and the channel contraction area plays a decisive role in the enhancement of the cooling effect. The heat transfer capacity of the sinusoidal corrugated channel is closely related to the shape of the corrugation, and the heat transfer effect reaches for the best near the waveform H/L = 0.115. The physical mechanism of heat transfer enhancement of the corrugated channel is revealed in this paper, which can provide a reference for the design of the cooling structure of aeroengine blades in the future. [ABSTRACT FROM AUTHOR]

Generation of noise caused by the flow around a cylinder and its control are important in various engineering applications. Based on computational fluid dynamics with acoustic analogy and the vortex dynamics theory analysis, this study aims at investigating the ability of the wavy cylinder in improving aerodynamic performance and reducing aerodynamic noise. Noise control mechanisms with different Reynolds numbers are analyzed. The results show that the wavy cylinder is helpful for the reduction of the average drag coefficient and is efficient in suppressing fluctuation of the lift coefficient; consequently, the overall noise of the wavy cylinder is reduced. Specifically, the tonal noise is significantly suppressed or even eliminated under proper configurations. To explore the underlying noise suppression mechanisms, the process of vorticity generation around the wavy cylinder surface is examined in detail. The vorticity distribution on the surface of the wavy cylinder is profoundly improved, and the distribution of the boundary vorticity flux and boundary enstrophy flux is also remarkably weakened. As a result, the generation of vorticity near the wavy cylinder wall is diminished. These directly lead to a significant contraction of the vortex structure distribution in the wavy cylinder wake, especially for some large-scale vortex structures. Moreover, periodic vortex shedding is significantly suppressed in the case with high Reynolds numbers, which might be the main reasons for noise reduction. The interaction area of the positive and negative Lamb vector divergence, which is closely related to the noise generation, is decreased. This contributes to drag reduction and noise attenuation. This indicates that drag reduction and noise suppression are closely bounded in the wavy cylinder. [ABSTRACT FROM AUTHOR]

Angiogenesis plays an important role in tumor growth and expansion, which makes it one of the most critical subjects in oncologic research. Angiogenesis can be imaged with photoacoustic microscopy (PAM), however the lateral resolution deteriorates significantly out of focus. Virtual-point-detector-based synthetic aperture focusing technique (SAFT) combined with the coherence weighting factor (CF) can alleviate the blurring, at a cost of anisotropy of resolution. In this study, a two-dimensional SAFT with CF was investigated to improve resolution and yield lateral resolution isotropy simultaneously. In a phantom study, two carbon fibers with a diameter of 6 μm fixed perpendicularly to each other were imaged with PAM developed in our laboratory. In the depth range of 0.6 mm near the focal spot, the best resolution processed with one-dimensional (1D) SAFT is 40 μm better than that processed with two-dimensional (2D) SAFT. However, the maximum difference in lateral resolution between the z-x and z-y planes is about 15 μm processed with 2D SAFT, while it is 145 μm processed with 1D SAFT. Furthermore, the 2D SAFT increased the signal-to-noise ratio (SNR) by up to 8 dB higher than 1D SAFT at an imaging depth of 700 μm below the focal spot. Finally, in vivo imaging of the dorsal subcutaneous microvasculature of a mouse was used to validate the improved performance of 2D SAFT. [ABSTRACT FROM AUTHOR]

A cell-centered spatiotemporal coupled method is developed to solve the compressible Euler equations. The spatial discretization is performed using an improved weighted essentially non-oscillation scheme, where the Harten–Lax–van Leer–contact approximate Riemann solver is used for computing the numerical fluxes. A two-stage fourth-order scheme is adopted to carry out time advancement for unsteady problems. The proposed method is featured by spatiotemporal coupling time-stepping that can be generalized without using the case-dependent generalized Riemann problem solver. A number of one- and two-dimensional test cases are presented to demonstrate the performance of the proposed method for solving the compressible Euler equations on structured grids. The numerical results indicate that the novel method can achieve relatively large Courant–Friedrichs–Lewy (CFL) number compared to other studies that implement the two-stage fourth-order scheme, and that it is more capable of capturing small-scale flow structures than the Runge–Kutta (RK) method. [ABSTRACT FROM AUTHOR]

Efficient prediction and evaluation of noise performance are crucial to the design and the optimization of landing gear noise. A systematic method is developed to predict and evaluate landing gear noise in the present study, termed as noise spectrum deep learning model (NSDL). In this algorithm, the encoder and decoder are designed to extract noise features and reconstruct noise data. Specifically, a loss function that takes the identification of both broadband noise and tone noise into account is utilized to guide the training direction of the model, aiming to improve the training efficiency and prediction results of the model. Afterward, the mapping relationship between landing gear experimental parameters and noise features is established by multi-layer perceptron. In this study, the detail of the algorithm is analyzed and discussed based on the results of wind tunnel noise experiment and numerical simulation. The results show that the proposed model can effectively and precisely predict landing gear noise under various conditions, including different flow speeds, angles of attack, number of wheels, and heights of the main strut. For the inflow velocity range of 34–75 m/s, the average error of the overall sound pressure level is restricted below 0.83% (0.6 dB). In case only the angle of attack is changed, the average error is reduced to be less than 0.36% (0.3 dB). The prediction results show that the landing gear noise is mainly broadband noise and tone noise mainly appears in the low frequency and intermediate frequency. With the increase in the inflow speed, the broadband noise increases gradually, and the frequency of tone noise gradually shifts to the high frequency band. Additionally, it is found that, for landing gear with four or six wheels, noise is very sensitive to angles of attack and wheel angles of attack. Consequently, the NSDL method shows significant potential in predicting the sound pressure level of landing gears and is expected to improve the efficiency of evaluation and optimization design for noise reduction of landing gear. [ABSTRACT FROM AUTHOR]