泥化夹层强风化砂岩边坡滑坡治理

在大多数工程项目中都存在边坡滑坡现象,龙井至大蒲柴河段高速公路也面临着这样的问题,在泥化夹层强风化砂岩地段存在着严重的边坡滑坡现象,边坡滑坡是一种很难治理的病害,通过对滑坡体现场进行详细的勘察,确定滑坡形成的主要原因,采取合理有效的防治方案,综合治理,并保证对滑坡治理目的的实现。本文分析了泥化夹层强风化砂岩边坡滑坡的主要成因,探讨了边坡滑坡的防治方法。</jats:p

A numerical toolkit for the ignition delay time and ignition probability density predictions based on instantaneous mixing fields in OpenFOAM

The OpenFOAM built-in chemistry solver, chemFoam, is extended as multiMeshChemFoam to simultaneously calculate the zero-dimensional (0D) ignition processes on the entire computational domain of practical simulations. The instantaneous temperature, pressure, and species mass fractions of a mixing field are input for the ignition calculation. A solver termed idtFoam is then developed to extract the Ignition Delay Time (IDT) on all cells from the 0D calculations. Several ignition criterions including the temperature exceeds a threshold value, the peaks in heat release rate (or equivalently, the time derivative of temperature) and species mass fractions are available. Another solver denoted as ipdFoam is finally compiled to construct the Ignition Probability Density (IPD) on the entire domain for a certain period. A time series of transient data from the mixing field are necessitated for the ignition calculation, IDT extraction, and IPD construction on individual cells. The numerical toolkit is verified with chemFoam for the 0D ignitions of ethylene. It is then applied to the mixing fields of an ethylene-fueled model supersonic combustor. It is computationally-efficient to evaluate the ignition performance of practical combustion systems in the design phase. Furthermore, assessment on the ignition properties can be made prior to any detailed and computationally-expensive simulations on the reactive flow, since only mixing field is required for calculating the IDT and IPD

High-order simulation solving Navier-Stokes equations with Spalart–Allmaras turbulence model

The goal of this paper is to implement an accurate and robust solver for compressible Navier-Stokes equations coupled with the Spalart&ndash;Allmaras model, which possesses the capability of shock-capturing and predication of boundary layer and separated flow. In a given stencil width, a WENO-Z scheme equipped with Roe flux difference split method is used to calculate the inviscid flux, and central differencing scheme for the viscous terms are employed. The explicit Runge-Kutta is adopted for the temporal discretization. The simulation results of selected cases are given to verify the validation of the solver.</p

Numerical study on the shock/combustion interaction of oblique detonation waves

To determine the shock/combustion interaction structure of a wedge-induced oblique detonation wave, high-order numerical simulations solving the two-dimensional reactive Euler equations embedded with a two-step chemical kinetic model have been performed. In this study, various dimensionless heat release amounts ranging from 40.0 to 52.5 are selected to investigate the flow configuration. The computational results show that four types of typical shock/combustion interactions, namely, Type VI, I, V and IV (following the classification of shock/shock interaction proposed by Edney), can be observed. The detailed structures and characteristics of the interaction types are presented and shown to be different than the classic shock/shock interaction. Additional insight into the transition principles of different shock/combustion interactions is illustrated through shock polar analysis. (C) 2020 Elsevier Masson SAS. All rights reserved

External-Compression Supersonic Inlet Free from Violent Buzz

To greatly improve the supersonic inlet stability at low cost of structural weight and complexity, a novel buzz suppression strategy based on fixed-geometry air bleed is developed. It is designed to have plenty of narrow flush slots that are widely distributed along the compression surface. Using the natural pressure gradient varying with the terminal shock position, it is capable of creating self-adaptive bypass flow removal upstream of the internal duct. A strong stabilizing effect can be thus automatically produced on the subcritical flowfield by eliminating shock-induced separation and discharging excessively captured airflow. Simultaneously, the undesired air leakage at the critical regime can be naturally restricted to prevent a prohibitive performance penalty during normal operation. To verify the effectiveness, an external-compression inlet model is specially designed and carefully tested at freestream Mach numbers of 2.0 and 2.5 with an almost full exit throttle range considered (0-99.1%). Results indicate that the subcritical stable-flow range is remarkably extended from a throttle threshold of 53.7% to that of 86.4% and 73.7%, respectively, after the usage of the proposed bleed method. Moreover, intense flow instability is totally eliminated, even when the duct exit is almost closed. Further analysis reveals that the bleed flow rate at the near-critical state is not beyond 1% of the inlet flow rate for both freestream conditions. It actually causes no obvious loss of the inlet flow rate. Also, the following total pressure drop and drag increase are below 0.4%. Additionally, the observed unique buzz flow implies that the buzz origin is not necessarily limited to the two known sources, as opposed to the long-established understanding

Numerical investigation of mode transition and hysteresis in a cavity-based dual-mode scramjet combustor

The effect of ethylene fuel equivalence ratio (ER) variation directions on combustion states in a dual-mode scramjet combustor was numerically investigated. The combustor employed transverse wall fuel injectors and downstream cavity flameholders without pilot fuel, which are fundamental components in many practical combustors. The isolator inflow Mach number was 3.1, and static pressure, stagnation pressure and stagnation temperature were 53 kPa, 2622 kPa and 1656 K, respectively. The ER was regulated abruptly in a piecewise constant manner, from 0.10 to 1.02, and then back to 0.10. A 3-D URANS method with a recognized two-step kinetics model was adopted. Results exhibited two combustion hysteresis loops, which indicated that different types of combustion mode transitions could result in hysteresis. The first was a hysteretic phenomenon between separated and shock-free scramjet modes based on steady quasi-one-dimensional combustor flow assumptions, and the second was between two different patterns of separated scramjet modes. Hysteresis mechanisms are elucidated from the viewpoint of combustion flow structures. The first hysteresis was attributed to flame stabilization mode transitions between the cavity shear-layer stabilized mode and the jet-wake stabilized mode, along with the transition hysteresis of a pre-combustion shock train's establishment and vanishment. The flame stabilization locations were greatly influenced by the flow separation states ahead of the fuel injectors, and the flow separations were in return determined by the flame distributions. The second hysteresis was attributed to transitions between weak-oscillation mode and intensive-oscillation mode with the transition hysteresis of shock reflection amount increase and decrease of the pre-combustion shock train structure, which were both in the jet-wake stabilized location. Flame in the low-speed region beside the separation bubbles ahead of the fuel injectors provided heat and hot radicals for downstream flame stabilization, and the pre-injector flame intensity greatly influenced the combustion oscillation states. (C) 2019 Elsevier Masson SAS. All rights reserved

一种进气道定堵塞度自起动试验装置

本发明公开了一种进气道定堵塞度自起动试验装置，包括:进气道，出口端设有延伸段：延伸段的内部设有堵块，两侧设有用于测量堵块位置的位移传感器，下端设有电磁铁；堵块与电磁铁通过堵块连接件连接，堵块连接件的一端与电磁铁的下端相接触，另一端与所述堵块固定连接；位移传感器包括传感器主体和滑动拉杆，滑动拉杆与堵块连接件固定连接；延时信号发生器，内部设有电磁铁电源；本发明进气道定堵塞度的自起动试验装置在获得了完整不起动振荡周期的同时，还在风洞有效运行时间范围内对其自起动过程进行了考察，且借助位移传感器对该过程进行了定量记录，保证了自起动试验的有效性和可重复性

内压缩波系对高超声速进气道自起动性能影响研究

为了探究进气道肩部膨胀扇以及不同压缩方式对进气道自起动性能的影响,结合具体的进气道构型,针对不同的压缩角、边界层厚度开展了马赫数4.0级的风洞试验研究。结果表明:在不起动分离区同侧的膨胀扇会对当地气流加速,降低局部压强,进而对压缩激波较强时的进气道自起动过程有明显改善。而唇罩分级压缩对二元进气道的自起动能力也有提高效果。此外,对比侧压模型与顶压模型的试验结果发现,边界层厚度对侧压模型自起动性能的影响趋势与顶压式存在明显的差异。与此同时,当自起动受限于几何喉道的进气道构型,压缩方式对进气道自起动性能的影响不明显,但是对于由压缩激波-边界层干扰诱导分离区形成的气动喉道决定能否起动的进气道,侧压方式有利于提高进气道的自起动性能

Hysteresis of Shock Train Movement in the Isolator with a Ramp

Inside the dual-mode scramjet engine, the shock train will move to a new location when the backpressure changes. Few works focus on the response of the shock train position to the backpressure cyclic variation. This work aims to investigate the behavior of the shock train under such backpressure conditions. Experiments were carried out in a Mach 3 direct-connect facility. The isolator is equipped with a ramp that is used to improve the isolator performance. The static pressures along the wall centerlines were measured. The schlieren imaging was used to provide flow visualization. The results show that a significant hysteresis occurs in the shock train position during the backpressure cyclic variation process. It is found that a large-scale subsonic wake flow region forms behind the rampwhen the shock train reaches the ramp trailing edge. The capability of the ramp to retain the existence of the wake flow determines the occurrence of the hysteresis. The effects of the ramp height and width on the hysteresis were examined. Based on the experimental data, the oscillation characteristics were discussed by using wavelet analysis and cross-spectrum analysis. The coupled oscillation between the shock train oscillation and the backpressure oscillation was observed

Simple shape model for normal shock trains in straight channels

Normal shock trains are a flow phenomenon of significance to ramjet engines, but it remains unclear what its structure is decided by and how it evolves with the incoming Mach number. To seek a theoretical explanation, the minimum entropy production principle is generalized to the quasi-steady behavior of normal shock trains in two-dimensional straight channels with uniform incoming flow. Numerical simulations are also performed to validate the model together with the data collected from public literature. The analysis suggests that the flow parameters of a normal shock train depend on the inviscid shock-shock interactions rather than the local boundary-layer separations, though the angles of two incident shocks should still be equal as similar to the case that complies with the free-interaction theory. The shock feet's positions, meanwhile, are allowed to be coincident or not, free from the entropy restriction. This freedom of position explains why both symmetric and partially asymmetric normal shock trains could be found previously. Further theoretical calculations reveal the inclinations of two incident shocks increase first and then decrease with the incoming Mach number, peaking at 48.570 degrees when the Mach number reaches 1.753. It is also indicated that the Mach number range allowing for a normal shock train is 1.652 to 2.254, giving evidence for past observations