Abstract
Experimental research of the turbulent swirl flow in the pipe behind the axial fan impeller is presented in this paper. Axial fan is inbuilt without guide vanes in the installation with a free inlet and ducted outlet, like it is widely used in the ventilation systems. One-component laser Doppler anemometry and stereo particle image velocimetry (SPIV) are used in two measuring sections on the fan pressure side and for three fan rotation numbers. Non-dimensional axial velocity profile is not significantly transformed downstream, while the circumferential is, although it preserves its character. Turbulence level is the highest in the vortex core in both measuring sections for all velocities. It increases downstream in the vortex core zone and decreases in the main flow region. Determined skewness and flatness factors point out the intermittent character of the generated turbulent swirl flow, as well as the existence of the organized coherent structure. Correlation curves indicate various dynamics of fluctuating circumferential velocity fields in measuring points. The Rankine vortex structure of the turbulent swirl flow is also revealed by the SPIV measurements. Analysis shows more dominant vortex core dynamics in the downstream section. Studied flow is characterized by extensive mass, momentum and energy transfer.
Highlights
This paper presents a study of the turbulent swirl flow on the axial fan pressure side by the use of the laserbased, measuring techniques such as particle image velocimetry (PIV) and laser Doppler anemometry (LDA) in the ventilation ducts
The turbulent vortex core is formed, known as the forced vortex region, with the solid body distribution of circumferential velocity, where W ∝ r. This domain, with a shear layer characterized by W ≈ Wmax, is connected to the sound flow region or free vortex, where U ≈ const, and circumferential velocity has the distribution of the potential swirl W ∝ 1/r
Designed axial fan impeller was used without guide vanes to generate the turbulent swirl flow in the pipe
Summary
This paper presents a study of the turbulent swirl flow on the axial fan pressure side by the use of the laserbased, measuring techniques such as particle image velocimetry (PIV) and laser Doppler anemometry (LDA) in the ventilation ducts. The paper’s focus is on the turbulent swirl flow generated by the axial fan in a straight pipe It is inbuilt without guide vanes in the installation with a free inlet and ducted outlet categorized as B installation type in ISO 5801. The turbulent swirl flow with the Rankine vortex structure, generated by the specially designed axial fan, survived till the downstream measuring section, which is almost at the test rig outlet. Flow at the inlet is fully developed with a symmetrical air velocity profile and it is free of swirl This is checked by use of the smoke visualization technique. Measurements were performed on the characteristic axial fan impeller rotation number n = 1000, 1500 and 2000 rpm, which generated the extensively turbulent swirl flow
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