湍流转捩是流体从层流稳定状态到湍流混沌状态的过渡，是自然界和工程应用中广泛存在的现象，是流体力学中的前沿问题。层流向湍流的转捩伴随着壁摩擦和热交换，对精细化捕捉流场特征、准确预测气动数据至关重要。大分离流动是流体流动的常见现象，广泛存在于航空航天等领域。大分离流动会造成非定常涡脱落，引起非定常气动力、气动噪声和结构疲劳。准确预测转捩和大分离流动对提高飞行器、叶轮机等装置的性能和效率具有重要意义。 为了准确预测不同因素诱导的转捩、捕捉大分离流动特征，本文主要完成了以下工作： （1）采用模块化编程思想，搭建了基于块结构网格的，单元中心型有限体积法的，并行Navier-Stocks方程求解器架构。程序从前处理到迭代计算再到后处理完全并行化，其模块包括前处理、时间推进、空间重构、空间离散、湍流模型、加速手段等。 （2）对Menter和Langtry提出的湍流转捩模型进行修正。在保证不影响原始模型预测能力的前提下，采用湍动能输运方程添加源项的方式，进行自由湍流度衰减修正、弯曲和流线曲率修正；采用动量厚度雷诺数输运方程添加源项的方式，进行横流转捩修正。 （3）将修正后的转捩模型进行推广。分别利用延迟脱落涡模拟(DDES)和混合模型（Hybrid RANS/LES）的思想，在近壁面附近采用修正后的湍流转捩模型，在其他区域采用亚格子模型求解流场，推广得到基于转捩模型的混合模型。

Turbulent transition is the transition from the steady state of the laminar flow to the turbulent flow, which is a commonly observed phenomenon in nature and engineering applications and a research field on the most advancing front of fluid mechanics. The transitions from laminar to turbulent flow are accompanied by wall friction and heat exchange, which is very important for capturing the flow characteristics exactly and correctly predicting the aerodynamic performances. Massively separation flows are a commonly observed phenomenon in aeronautics, astronautics and so on. The massive separation flow may cause to unsteady vortex shedding, which coupled with unsteady force, acoustics generation, vibrations of solid frame. The precise prediction of transition is of great significance for improving the performance and efficiency of aircraft and turbomachinery. In order to predict the transition induced by different factors accurately, and capture the characteristics of massively separation flows, the specific main works of the thesis are the following aspects: (1) Adopt modular programming ideas, cell-centered finite volume parallel Navier-Stocks solver was bulit based on the framework of multiblocks. All the processes from preprocessing to iterative solution to post processing are parallelizable, which include preprocessing, time marching, spacial construction, spacial discretization, turbulent modeling and acceleration techniques. (2) Modified the turbulent transition modeling proposed by Menter and Langtry. On the promise of keeping original simulation ability, the transition modeling considering turbulence intensity decay and curvature correction was developed by adding a source term to turbulent energy transition equation, and the cross flow induced by transition was corrected by adding a source term to the momentum thickness Reynolds number transport equation. (3) Using the delayed detached eddy simulation (DDES) and Hybrid RANS/LES coupling with the modified transition modeling to simulate the flow field, in which the modified turbulent transition model is only used in the near wall surface regions and the subgrid turbulent model is used in other regions.