Defocusing PTV Applied To An Open Wet Clutch – From Macro To Micro

The approach of defocusing particle tracking velocimetry (defocusing PTV) is applied in various levels of magnification to the fluid flow of an open wet clutch with radial grooving. The magnification ranges from M=0.8 up to M=15, whereas corresponding defocusing sensitivities ranges from 67.1 to 9.0 µm/pixel. This specific set-up appears necessary, since a comparative wide field-of-view as well as a detailed consideration inside the groove seems equally important for this particular scenario. It can be shown that all optical configurations can properly depict the occurring fluid flow phenomena that are present in an open wet clutch. The smallest magnification can properly depict the region between the inner and the outer radius and is thus closing the academic gap for open clutch flows, since a groove-to-groove analysis as well as an evaluation along the entire radius becomes possible. The smallest magnification yields the highest accuracy in terms of {x,y} and also in z-direction. The accuracy in z-direction is quantified with the region near to the stator, where the theoretical axial velocity should be zero. The set-up with M=0.8 reaches an uncertainty of the particle-image diameter of 2σ_di=0.24 pixel. The remaining set-ups have higher uncertainties. The smaller defocusing sensitivity cannot outperform the loss in intensity and a less distinct intensity peak at the outer part of the defocused image due to the large magnification and the used Questar lens. These findings are supported by a fluid flow analysis, where the circumferential velocity u_φ in the middle of the groove is used as comparative case. All magnifications were able, to depict the considered velocity properly, while the uncertainty increases for higher-magnification configurations. In summary, the present study demonstrates the feasibility and robustness of the defocusing PTV-approach for such sub-millimeter gap-flow scenarios in technical applications. The flexibility in terms of magnification reached within this experimental investigation makes defocusing PTV a candidating technique for such industry-relevant research scenarios.