哥伦比亚VS-6、VS-8井固井问题分析及其对策

哥伦比亚Vigia Sur油田VS-6、VS-8两口井固井质量不合格导致无法生产,USIT成像测井测得环空窜槽严重,通过分析水泥浆的流变性、注替参数、前置液用量、居中度、施工过程等因素,找出顶替效率低的主要原因,提出改进措施并应用于VS-7、VS-9两口井,取得了良好效果,固井质量达到了全井优质,为今后该地区固井提供了成功经验。

高速自然层流翼型高效气动稳健优化设计方法

先进高速高升力自然层流(NLF)翼型的设计已经成为提高新一代高空长航时(HALE)无人机(UAV)性能的重要手段。然而这类翼型表面极易出现分离泡和激波等,尤其对于马赫数、飞行攻角等状态波动气动特性非常敏感,这导致传统的层流翼型设计方法设计的外形在面向工程应用中出现稳健性差,难以被工程使用。气动稳健设计(RADO)方法虽然是一种有希望的解决途径,但它遭遇了巨大计算花费的难题。为了解决这些问题,通过对影响气动稳健优化设计效率的关键技术进行研究,发展了基于自适应前向-后向选择(AFBS)的稀疏多项式混沌重构方法,极大改善了不确定分析(UQ)和稳健优化效率。同时,也发展了考虑多参数不确定的高效气动稳健优化设计方法,有效解决了传统翼型设计方法难以满足高速高升力自然层流翼型设计要求兼顾高升力设计、自然层流设计以及超临界设计的难题。最后使用发展的方法成功设计了一类具有典型特点的跨空域稳健自然层流翼型。结果表明设计的翼型相对于经典的全球鹰无人机翼型气动性能全面提升,同时低阻范围更大,气动性能更加稳健,从而验证了稳健优化方法的有效性和相对于确定性设计的优势。

NONPARALLEL BOUNDARY LAYER STABILITY IN HIGH SPEED FLOWS

The parabolized stability equations （PSEs） for high speed flows, especially supersonic and hypersonic flows, are derived and used to analyze the nonparallel boundary layer stability. The proposed numerical techniques for solving PSE include the following contents： introducing the efficiently normal transformation of the boundary layer, improving the computational accuracy by using a high-order differential scheme near the wall, employing the predictor-corrector and iterative approach to satisfy the important normalization condition, and implementing the stable spatial marching. Since the second mode dominates the growth of the disturbance in high Mach number flows, it is used in the computation. The evolution and characteristics of the boundary layer stability in the high speed flow are demonstrated in the examples. The effects of the nonparallelizm, the compressibility and the cooling wall on the stability are analyzed. And computational results are in good agreement with the relevant data.

The properties of dilute debris flow and hyper-concentrated flow in different flow regimes in open channels

Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow(k/K<0.1); transitional flow(0.1< k/K<1); and turbulent flow(k/K>1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyperconcentrated flow.

Turbulent Energy Budgets of a Ground Vortex Flow

Turbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane of symmetry by quadratic interpolation of the LDV （Laser Doppler Velocimetry） measurements, for a wall jet-to-boundary layer velocity ratio of 2. The results, which have relevance to flows encountered in powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow. The analysis of turbulent energy equation terms using the measured data revealed that production by normal and shear stresses are both very important to the turbulent structure of the impact zone of the ground vortex. This is an indication that the modeling of turbulence of a ground vortex requires a good representation of the production by normal stresses which is most important in the collision zone.

Hypersonic flow control of shock wave/turbulent boundary layer interactions using magnetohydrodynamic plasma actuators

The effect of magnetohydrodynamic(MHD)plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low magnetic Reynolds number approximation.A Mach 5 oblique shock/turbulent boundary layer interaction was adopted as the basic configuration in this numerical study in order to assess the effects of flow control using different combinations of magnetic field and plasma.Results show that just the thermal effect of plasma under experimental actuator parameters has no significant impact on the flow field and can therefore be neglected.On the basis of the relative position of control area and separation point,MHD control can be divided into four types and so effects and mechanisms might be different.Amongst these,D-type control leads to the largest reduction in separation length using magnetically-accelerated plasma inside an isobaric dead-air region.A novel parameter for predicting the shock wave/turbulent boundary layer interaction control based on Lorentz force acceleration is then proposed and the controllability of MHD plasma actuators under different MHD interaction parameters is studied.The results of this study will be insightful for the further design of MHD control in hypersonic vehicle inlets.

Towards an entropy-based detached-eddy simulation

A concept of entropy increment ratio （ s- ） is introduced for compressible turbulence simulation through a series of direct nu- merical simulations （DNS）. s- represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f, to describe the boundary layer region and propose an entropy-based detached-eddy simulation method （SDES）. This approach follows the spirit of delayed de- tached-eddy simulation （DDES） proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performanc- es are compared in the following flows, namely, pure attached flow with thick boundary layer （a supersonic fiat-plate flow with high Reynolds number）, fully separated flow （the supersonic base flow）, and separated-reattached flow （the supersonic cavity-ramp flow）. The Reynolds-averaged Navier-Stokes （RANS） resolved region is reliably preserved and the modeled stress depletion （MSD） phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions.

Problems of the conventional BL model as applied to super/hypersonic turbulent boundary layers and its improvements

Turbulence modeling has played important roles in solving engineering problems. However, with the development of aero-space technology, turbulence modeling faces new challenges. How to further improve turbulence modeling for su-per/hypersonic flows is an urgent problem. Through analyzing a set of data resulting from DNS and experiments, it is foundthat some most popular models suffer from essential flaws, and can be hardly improved following the traditional mode ofthinking. On the contrary, the BL model, which is one of the simplest and widely-used models, can be further improved. In thispaper, through analyzing results from DNS data, the main cause of the inaccuracy in applying the BL model to supersonic andhypersonic turbulent boundary layers is found to have resulted from the mismatch between the location of the matching pointof the inner and outer layers of the BL model determined by the conventional way and those given by DNS. Improvement onthis point, as well as other improvements is proposed. Its effectiveness is verified through the comparison with DNS results.

A three-equation turbulence model for high-speed flows

Adding a new equation to the two-equation K-turbulence model framework,this paper proposed a three-equation turbulence model to determine the density variance for high-speed aero-optics and high-speed compressible turbulent flows.Simulations were performed with the new model for supersonic and hypersonic flat-plate turbulent boundary layer and hypersonic ramp flows.The results showed that the prediction with the present model agrees well with the experimental data and is significantly better than the Lutz's model in predicting the density variance for the flat-plate flows.Furthermore,the present model can produce more accurate skin pressure and skin heat flux distributions than the original K-model in simulating hypersonic compression ramp flows with separation and reattachment and shock/boundary layer interactions.Without introducing a variety of ad hoc wall damping and wall-reflection terms,the proposed three-equation turbulence model is applicable to highspeed aero-optics and turbulent flows of real vehicles of complex configuration.