Effects of wall temperature on boundary layer stability over a blunt cone at Mach 7.99

Effects of wall temperature on stabilities of hypersonic boundary layer over a 7-degree half-cone-angle blunt cone are studied by using both direct numerical simulation (DNS) and linear stability theory (LST) analysis. Four isothermal wall cases with Tw/T0= 0.5, 0.7, 0.8 and 0.9, as well as an adiabatic wall case are considered. Results of both DNS and LST indicate that wall temperature has significant effects on the growth of disturbance waves. Cooling the surface accelerates unstable Mack II mode waves and decelerates the first mode (Tollmien–Schlichting mode) waves. LST results show that growth rate of the most unstable Mack II mode waves for the cases of cold wall Tw/T0=0.5 and 0.7 are about 45% and 25% larger than that for the adiabatic wall, respectively. Numerical results show that surface cooling modifies the profiles of rdut/dyn and temperature in the boundary layers, and thus changes the stability haracteristic of the boundary layers, and then effects on the growth of unstable waves. The results of DNS indicate that the disturbances with the frequency range from about 119.4 to 179.1 kHz, including the most unstable Mack modes, produce strong mode competition in the downstream region from about 11 to 100 nose radii. And adiabatic wall enhances the amplitudes of disturbance according to the results of DNS, although the LST indicates that the growth rate of the disturbance of cold wall is larger. That because the growth of the disturbance does not only depend on the development of the second unstable mode

分辨率优化的混合WENO格式

为提高有限差分格式的分辨率,利用傅里叶分析对WENO格式进行色散及耗散优化,并给出优化的线性权重.用优化后的WENO格式与保单调格式（MP）进行加权混合,得到新的加权混合WENO格式（H-WENO）.通过一维激波管问题、Shu-Osher问题及二维双Mach反射问题及R-T不稳定性问题对格式进行数值测试.结果显示,新格式具有强健的激波捕捉能力和对小尺度波结构的高分辨率,与原WENO格式相比改进明显

Nonlinear spectral-like schemes for hybrid schemes

In spectral-like resolution-WENO hybrid schemes, if the switch function takes more grid points as discontinuity points, the WENO scheme is often turned on, and the numerical solutions may be too dissipative. Conversely, if the switch function takes less grid points as discontinuity points, the hybrid schemes usually are found to produce oscillatory solutions or just to be unstable. Even if the switch function takes less grid points as discontinuity points, the final hybrid scheme is inclined to be more stable, provided the spectral-like resolution scheme in the hybrid scheme has moderate shock-capturing capability. Following this idea, we propose nonlinear spectral-like schemes named weighted group velocity control (WGVC) schemes. These schemes show not only high-resolution for short waves but also moderate shock capturing capability. Then a new class of hybrid schemes is designed in which the WGVC scheme is used in smooth regions and the WENO scheme is used to capture discontinuities. These hybrid schemes show good resolution for small-scales structures and fine shock-capturing capabilities while the switch function takes less grid points as discontinuity points. The seven-order WGVC-WENO scheme has also been applied successfully to the direct numerical simulation of oblique shock wave-turbulent boundary layer interaction

超/高超声速边界层湍流的马赫数壁温效应

本文利用空间发展的DNS数据,分析了马赫数为2.25,5,6和8的平板湍流边界层的热传导特性,及其对温度速度关系的影响。结果表明,当壁面温度取为近似恢复温度时,来流马赫数的变化对经典雷诺比拟影响不大:当马赫数达到8时,在强冷壁条件(T_w/T_r=0.18)下,边界层内存在较强的热流,经典的雷诺比拟已不再成立,各种改进的雷诺比拟在近壁出现振荡,也不再成立,本文给出了一种新修正的强雷诺比拟关系,较好地克服了上述缺点

高超声速小钝度球锥边界层转捩的攻角效应的直接数值模拟

直接数值模拟小钝度球锥(半锥度5°)在来流马赫数等于6,来流温度等于79 K(壁面温度等于3.72倍来流温度),雷诺数等于10000(以头半径为特征长度),攻角分别等于1°,3°,5°,10°这4种情况时边界层空间演化特征,得到了不同攻角时详细的边界层转捩位置,以及充分发展的湍流数据库,给出了可视化的流动形态,得到了大攻角时边界层对称分离流的数值模拟结果并给出了其变

超/高超声速平板湍流边界层的 DNS 和特征分析

本文给出了马赫数为2.25,5,6 和8 的平板可压缩边界层湍流空间发展的直接数值模拟(DNS)结果，通过分析受马赫数与壁面温度共同作用影响下的可压缩边界层湍流的特征，检验了压缩性效应和Morkovin 假设成立的范围.本文重点讨论了温度－速度关系，分析了强雷诺比拟受马赫数和壁温影响的规律.结果表明，当壁面温度取近似恢复温度时，来流马赫数（最大等于8）的变化对近壁湍流的压缩性效应的影响并不显著，Morkovin 假设依然有效；当马赫数达到8 时，压缩性效应受壁温影响显著，强冷壁条件（Tw/T∞=1.9）会大幅增加压缩性，导致Morkovin 假设不再严格成立

流向细纹平板边界层湍流减阻机理研究

本文针对Mach 2.25 平板边界层湍流，以直接数值模拟(DNS)为手段进行了流向条纹壁减阻研究。计算发现，当流向条纹间距为100 个壁面尺度时，具有最佳减阻效果。而减阻效果随条纹高度增加而加强，当条纹高度达到30 个壁面尺度时减阻效果相当明显。当全平板施加条纹壁时，由于抑制了壁面吹吸扰动的吸收性，流动不发生转捩。在转捩区及充分发展湍流区施加条纹壁虽不能完全抑制转捩，但仍有较好的减阻效果

入射激波-湍流边界层干扰的直接数值模拟

利用加权群速度控制格式(WGVC-M)格式,进行了入射激波-平板边界层湍流干扰的直接数值模拟(DNS)。流动参数为:来流Mach数2.3,入射激波角32°。利用该DNS结果,探讨了激波-边界层干扰及其形成的逆压梯度对湍流结构,统计特征以及湍能生成及分配机制的影响。利用DNS数据,分析了反射激波的展向变形以及流向的高频振荡和低频振荡特征。通过对比强分离情况和弱

自适应的高精度中心-WENO混合格式

为对可压缩流动进行高精度高分辨率的数值模拟,基于模板的光滑度量函数,构造了新型的加权因子,在此基础上将7阶精度的WENO格式与8阶中心格式进行加权组合,构造了一种自适应低耗散的中心-WENO混合格式(H-WENO7-CD8),并采用Fourier方法对离散格式数学特性进行了理论分析。该自适应的高精度中心-WENO混合格式相比于七阶的WENO格式具有更小的耗散误差。通过对激波-密度干扰问题、Rayleigh-Taylor不稳定性问题和双Mach反射问题的数值模拟,并与WENO-JS格式的计算结果对比,结果表明:该格式结合了WENO格式和中心格式的特点,能更好地捕捉激波,对物理脉动也具有较高的分辨率,适合于复杂流体流动的数值模拟

壁温对高超音速钝锥边界层稳定性的影响

高超音速边界层转捩预测是高超音速飞行器气动力及气动热分析的关键因素。作为高速飞行器的典型头部外形,钝锥边界层流动的转捩机理和转捩预测具有重要的实际意义,是目前研究高速飞行器气动力和气动热特征的重要课题。由于人们对影响转捩的物理机理并不是十分清楚,因此,目前对于高超音速边界层的转捩的预测多采用半经验的方法,很多经验参数还依赖实验给定