Transonic Blade Design: Quo Vadis?

Abstract The design of efficient transonic fan and compressor airfoils is still a major challenge. Efficiency in this context means the lowest possible losses and a wide, stable operating range. The challenge is mainly due to the presence of shock waves, their complex structures and highly unsteady behavior. The aim of this research is to provide appropriate technical solutions to this design challenge. To this end, this paper provides a brief status report and deduces what research activities will be important and necessary in the future. As a first step, it focuses on the description of the three main flow aspects that influence the loss generation and the operating range of transonic cascades. These are the leading edge flow, the pre-shock suction side flow region and the shock boundary interaction. The existing challenges for these three flow aspects and a possible solution approach are identified and discussed in the next step. The shock boundary layer interaction leads to significant shock oscillation, which reduces the operating range and also causes increased losses. This behavior and its effects have already been described in detail by the authors in previous publications, so for the sake of completeness they will only be touched upon briefly in this paper. Based on own studies as well as publications, the high improvement potential of flow control methods or a customized local design of the suction side shape is also briefly mentioned in the paper. The main focus of the work was on the influence of the leading edge shape and the pre-shock Mach number on the shock losses. For this purpose, individual optimizations were performed using the in-house optimizer AutoOpti coupled with the in-house flow solver TRACE at the aerodynamic design point of the DLR TCTA cascade. The optimizations were carried out only at one operating point and with limited release of the geometric parameters in order to be able to clearly distinguish the possible effects from each other. The results show that despite the use of a modern optimized transonic cascade as the initial geometry, further improvements can be achieved. Thus, the goal of quantifying the design potential is achieved with this first simple approach. A final theoretical evaluation of the improvement is made using the example of the transonic front stage of the DLR Rig 250 axial compressor.