Experimental and scale resolving numerical investigations of the physical performance of circumferential grooves in subsonic axial compressor stages

轴流压缩机用于燃气涡轮机装置和过程工程中，在经济上非常重要，对效率、压比和使用灵活性的要求不断提高。运行范围和效率在很大程度上取决于旋转和静止部件之间的径向间隙，该间隙随运行条件而变化。这些间隙不能以与叶片相同的方式缩放，使得压缩机设计中的当前趋势导致较大的相对间隙宽度。在转子上方的壳体中的周向凹槽可以减轻径向间隙的负面影响，但是特别是对于大间隙，只有不足的实验数据可用。为了对带周向槽的机匣处理进行数值设计，需要可靠的模拟工具。然而，现有技术的RANS方法在这方面存在缺陷。在这里，必须采用非定常连续性求解方法来确定效率和稳定性极限。然而，这些方法仍然需要改进，以利用可用的计算资源可靠地捕获高度复杂的物理机制。该项目将通过详细的调查来解决与周向槽的功能有关的未决问题。它将特别解决槽对效率的影响和稳定性极限附近的流动修改，以及不同阶段之间的相互作用。为了实现其目标，该项目将低速压缩机中的实验与连续性解决模拟相结合。由于所产生的数据具有互补性，这种方法产生了大量的附加值。这些实验提供了广泛条件下的全球数据，并采用更多涉及的技术，在选定的飞机上提供可靠的信息。昂贵的非定常模拟提供了对整个流动中各种效应相互作用的详细了解，例如在凹槽内部，并且可以通过实验进行验证。然而，这些模拟方法目前对于要解决的复杂流动来说还不够可靠。如果通过采用更粗的网格或更强的建模假设来减少大量的计算负担，则结果的质量可能会恶化，甚至低于标准方法的质量。因此，在该提案中，两个申请人联合起来为这里研究的情况创建实际适用的混合LES/RANS过程。这将通过推进现有办法以及通过深入的比较研究和制定最佳做法准则来实现。

Axial compressors, used in gas turbine installations and process engineering are highly important economically, with constantly increasing demands for efficiency, pressure ratio and flexibility of use. Operation range and efficiency heavily depend on the radial gaps between rotating and stationary parts, which vary with operation conditions. These gaps cannot be scaled in the same way as the blades, so that the current trends in the design of compressors lead to larger relative gap widths. Circumferential grooves in the casing above the rotors can alleviate the negative impact of the radial gaps, but in particular for large gaps only insufficient experimental data are available. To numerically design casing treatments with circumferential grooves requires reliable simulation tools. State of the art, however, are RANS methods which are deficient in this respect. Here, it is mandatory to employ unsteady turbulence-resolving approaches to determine efficiency and stability limit. These approaches, however, still require improvement to reliably capture the highly complex physical mechanisms with the available computational resources. The project will address the open questions related to the functioning of circumferential grooves by detailed investigations. It will particularly address the impact of the grooves on efficiency and flow modification near the stability limit, as well as the interaction between different stages. To reach its goals, the project combines experiments in a low-speed compressor with turbulence-resolving simulations. This approach generates substantial added value due to the complementary of the data being generated. The experiments provide global data over a wide range of conditions and, with more involved techniques, reliable information in selected planes. The costly unsteady simulations deliver detailed insight into the interaction of the various effects all over the flow, e.g. also inside the grooves, and can be validated with the experiments. These simulation methods, however, are presently not sufficiently reliable for the complex flows to be addressed. If the large computational burden is reduced by employing a coarser grid or by stronger modelling assumptions the quality of the results can deteriorate and even go below the quality of standard methods. Hence, in this proposal both applicants join forces to create a practically applicable hybrid LES/RANS procedure for the situations investigated here. This will be done by advancing present approaches as well as by intense comparative studies and formulation of best practice guidelines.