Abstract
The scope of this article is focused on general analysis of errors and uncertainties possibly arising from CFD-to-schlieren pictures matching. Analysis is based on classic analytical equations. These are firstly evaluated with the presumption of constant density gradient along the ray course. In other words, the deflection of light-ray caused by density gradient is negligible in compare to the cross size of constant gradient area. It is the aim of this work to determine, whether this presumption is applicable in case of supersonic air-to-air ejector. The colour and black and white schlieren pictures are carried out and compared to CFD results. Simulations had covered various eddy viscosities. Computed pressure gradients are transformed into deflection angles and further to ray displacement. Resulting computed light- ray deflection is matched to experimental results
Highlights
The basic idea of the Schlieren or knife-edge method for indicating small optical disturbances was described by Topler some eighty years ago, and thirty years later Rayleigh investigated the optical principles involved
It is the aim of this work to determine, whether this presumption is applicable in case of supersonic air-to-air ejector
Position of shear layer between primary and secondary streams was observed and its position is matched to those numerically predicted by various eddy viscosity models
Summary
The basic idea of the Schlieren or knife-edge method for indicating small optical disturbances was described by Topler some eighty years ago, and thirty years later Rayleigh investigated the optical principles involved. Nowadays the Schlieren method has become a standard tool for engineers in high-speed aerodynamics. It involves some uncertainty which requires an analysis. This analysis is usually being overcome or neglected. Once the experiment is completed, schlieren pictures can be used for flow analysis itself or for validation of numerically computed flow field. Schlieren pictures provide relatively cheap information about flow field and so the CFD does. The matching of its results is than the logical step in applied research when moving from experimental field into CFD base. The validation of CFD is usually done in conjunction with other experiments which allows some level of quantification
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