The last 20 years has seen the development of reliable, user-friendly, RANS CFD codes which can model the steady state features of complex flows. This coupled with the diminishing cost of computing power has made the solution of large problems economical. As result of this there has been a significant reduction in the amount of testing activity undertaken. Nevertheless, high quality experiments remain essential, and the real need is to effectively exploit the strengths of the two approaches. Whilst improvements in theoretical aerodynamic methods may be leading to a decline in test activity as a whole, paradoxically, it also means that when tests are carried out there is a need for the data to be of an ever increasing quality and quantity. There are two key commercial drivers acting on test activities which are: to achieve reductions in overall test costs and to reduce the test cycle time as a part of the broader goal of reducing time to market. The paper discusses the strengths and weaknesses of experimental and numerical methods, with reference to the limitations on resolution and intrusive effect of instrumentation, and the limitations of the physical models within numerical methods. From this conclusions are drawn regarding how the two approaches complement each other. The levels of accuracy and repeatability now required in turbomachinery testing are discussed with reference to work carried out at Cranfield University. The need for a continuous improvement in both capabilities and cost effectiveness of test facilities is identified.

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