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Pump impellers have to be designed from two separate points of view. From a hydraulic aspect the impeller has to fulfill the specified operating conditions for flow rate, head at the speed of rotation. Additionally, from the structural point of view, the impeller must be capable to resist mechanical loads. To fulfill nowadays requirements of flexible operating conditions, the mechanical design becomes more crucial, because of increased loads at part-load operation. Consequently, trustworthy information about deformation and stress are mandatory.
The present paper deals with the comparison of mechanical deformation of a pump impeller at design and off-design operation. The full loading on the impeller caused by fluid pressure and centrifugal forces is considered in experimental and numerical investigations. Therefore, an experimental model pump, representing a repeating stage of a multistage boiler feed pump has been developed. Besides performance values, transient pressure and strain measurements at the back side of the impeller rear shroud are evaluated. For the strain measurements, strain gauges are used in Wheatstone bridges to evaluate transient data. For numerical simulations a one-way coupled Fluid Structure Interaction (FSI) model has been used. Transient Computational Fluid Dynamics (CFD) simulations have been performed for the complete model pump. For the turbulence modeling Menter’s SST model was used. In subsequent quasi-stationary Finite Elements (FE) simulations, the pressure loading on the impeller is taken from the CFD simulations for one impeller revolution.
Over the last few decades, several grid coupling techniques for hierarchically refined Cartesian grids have been developed to provide the possibility of varying mesh resolution in lattice Boltzmann methods. The proposed schemes can be roughly categorized based on the individual grid transition interface layout they are adapted to, namely cell-vertex or cell-centered approaches, as well as a combination of both. It stands to reason that the specific properties of each of these grid-coupling algorithms influence the stability and accuracy of the numerical scheme. Consequently, this naturally leads to a curiosity regarding the extent to which this is the case. The present study compares three established grid-coupling techniques regarding their stability ranges by conducting a series of numerical experiments for a square duct flow, including various collision models. Furthermore the hybrid-recursive regularized collision model, originally introduced for cell-vertex algorithms with co-located coarse and fine grid nodes, has been adapted to cell-centered and combined methods.
Die direkte Simulation aeroakustischer Phänomene ist bis heute eine der großen Herausforderungen in der numerischen Aeroakustik (CAA). In diesem Zusammenhang erweisen sich moderne Lattice-Boltzmann Verfahren als äußerst effizient, insbesondere im Hinblick auf Rechenzeit, Stabilität und Genauigkeit. Die geringe numerische Dissipation und Dispersion dieser Methoden sind dabei von zentraler Bedeutung.Im vorliegenden Beitrag diskutieren wir die Anwendung einer modernen Lattice-Boltzmann Methode auf aeroakustische Problemstellungen. Nach einem kurzen Überblick zu den mathematischen Grundlagen der Methode präsentieren wir erste Simulationsergebnisse für industrielle Anwendungen.
The natural polymer chitin is an abundant source for valuable N-acetylchitooligosaccharides and N-acetylglucosamine applicable in several industries. The endochitinase Chit36-TA from Trichoderma asperellum was recombinantly expressed in Komagataella phaffii for the enzymatic degradation of chitin from unused insect exuviae into N-acetylchitooligosaccharides. Chit36-TA was purified by Ni–NTA affinity chromatography and subsequently biochemically characterized. After deglycosylation, the endochitinase had a molecular weight of 36 kDa. The optimum pH for Chit36-TA was 4.5. The temperature maximum of Chit36-TA was determined to be 50 °C, while it maintained > 93% activity up to 60 °C. The chitinase was thermostable up to 45 °C and exhibited ~ 50% activity after a 15 min incubation at 57 °C. Chit36-TA had a maximum specific enzyme activity of 50 nkat/mg with a Km value of 289 µM with 4-methylumbelliferyl-N,N′,N″-triacetyl-β-chitotrioside as substrate. Most tested cations, organic solvents and reagents were well-tolerated by the endochitinase, except for SDS (1 mM), Cu2+ (10 mM) and Mn2+ (10 mM), which had stronger inhibitory effects with residual activities of 3, 41 and 28%, respectively. With a degree of hydrolysis of 32% applying colloidal shrimp chitin (1% (w/v)) and 12% on insect larvae (1% (w/v)) after 24 h, the endochitinase was found to be suitable for the conversion of colloidal chitin as well as chitin from black soldier fly larvae into water-soluble N-acetylchitooligosaccharides. To prove scalability, a bioreactor process was developed in which a 55-fold higher enzyme activity of 49 µkat/l and a tenfold higher protein expression of 1258 mg/l were achieved.