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Vortex breakdown in a pump sump is a complex and negative factor for the pump. Different from my previous study that focused mainly on the development process of vortex and its damage to the pump, this paper is from a new perspective that studies the energy dissipation and time–frequency characteristics induced by vortex breakdown. The tested data of pressure and velocity in the process of vortex breakdown were obtained by the model. Considering the gas–liquid two-phase flow of the vortices, a new numerical simulation approach is conducted and verified. The results show that the development rules of vortex breakdown reveal that the breakdown is initiated near the blade. The residual disturbance in the flow field continues to propagate after vortex breakdown, inducing unstable flow inside the runner and causing additional energy dissipation. The time–frequency characteristics induced by vortex breakdown indicated that the runner rotation speed has a significant effect on the vortex breakdown. The frequency of vortex breakdown is relatively small under high-speed rotation. Through discussion, it can be concluded that in order to reduce the harm of vortex breakdown, it can take measures such as controlling the impeller rotation speed, stalling anti-vortex measures, and adjusting operating conditions. [ABSTRACT FROM AUTHOR]

Ericoid mycorrhizal associations are a symbiotic relationship between soil fungi and ericaceous plants. Diversity of fungi associated with hair roots of ericaceous plants may vary as a result of frequent disturbances by human activities. The fungal diversity and communities associated with hair roots of Rhododendron ovatum were investigated along a human disturbance gradient in subtropical forests of China. Nine hundred fungal operational taxonomic units were determined by high-throughput sequencing, including different phyla such as Ascomycota, Basidiomycota, Zygomycota, Chytridiomycota, and Glomeromycota. The dominant phylum in Cunninghamia lanceolata plantations and old-growth forest was Ascomycota, while Basidiomycota was the dominant phylum in secondary forests. The indicator species analyses showed that more pathogenic indicator fungi appeared in the disturbed forests, whereas more putative ericoid mycorrhizal fungi existed in the old-growth forests. Principal component analysis also showed that the fungal communities in the hair roots of R. ovatum were distinct between natural forests and plantations, suggesting that the fungal communities associated with hair roots of R. ovatum after logging were resilient and could recover to predisturbance status. The results of envfit analysis showed that performance of host plants rather than accompanying plant community and soil parameters of plots was the key determinant of the root-associated fungal community of R. ovatum. Key words: Rhododendron ovatum, fungal diversity, human disturbance, subtropical forests, land use. Les associations mycorhiziennes ericoides sont des relations symbiotiques entre des champignons du sol et des plantes ericacees. La diversite des champignons associes aux poils racinaires des ericacees peut varier a la suite de frequentes perturbations causees par l'activite humaine. Les communautes et la diversite des champignons associes aux poils racinaires du Rhododendron ovatum ont ete etudiees le long d'un gradient de perturbation d'origine anthropique dans les forets subtropicales de la Chine. Au total, 900 unites taxonomiques operationnelles fongiques ont ete determinees par sequencage a haut debit, incluant differents phylums tels que: ascomycetes, basidiomycetes, zygomycetes, chytridiomycetes et glomeromycetes. Les ascomycetes etaient le phylum dominant dans les plantations de Cunninghamia lanceola et les vieilles forets tandis que les basidiomycetes dominaient dans les forets de seconde venue. Les analyses d'especes indicatrices ont montre que plus de champignons indicateurs pathogenes etaient presents dans les forets perturbees tandis que plus de champignons mycorhiziens, vraisemblablement ericoides, etaient presents dans les vieilles forets. L'analyse en composantes principales a egalement montre que les communautes fongiques presentes dans les poils racinaires de R. ovatum dans les forets naturelles etaient distinctes de celles rencontrees dans les plantations, indiquant que les communautes fongiques associees aux poils racinaires de R. ovatum apres la coupe etaient resilientes et pouvaient retrouver leur etat originel, avant la perturbation. Les resultats de l'analyse a l'aide de la fonction envfit ont montre que la performance des plantes hotes, plutot que la communaute vegetale compagne et les parametres du sol des parcelles, etait le facteur determinant de la communaute fongique associee aux racines de R. ovatum. [Traduit par la Redaction] Mots-cles: Rhododendron ovatum, diversite fongique, perturbation d'origine anthropique, forets subtropicales, utilisation des terres., Introduction Ericaceae is a large plant family, being distributed widely in heathlands (Toberman et al. 2008; Tejesvi et al. 2010) and most forest ecosystems, such as boreal coniferous forests (Perotto [...]