35 research outputs found
Decoupled CFD-based optimization of efficiency and cavitation performance of a double-suction pump
In this study the impeller geometry of a double-suction pump ensuring the best
performances in terms of hydraulic efficiency and reluctance of cavitation is determined using
an optimization strategy
, which was driven by means of the modeFRONTIER optimization
platform. The different impeller shapes (designs) are modified according to the optimization
parameters and tested with a computational fluid dynamics (CFD) software, namely ANSYS
CFX. The simulations are performed using a decoupled approach, where only the impeller
domain region is numerically investigated for computational convenience. The flow losses in
the volute are estimated on the base of the velocity distribution at the impeller outlet. The best
designs are then validated considering the computationally more expensive full geometry CFD
model. The overall results show that the proposed approach is suitable for quick impeller shape
optimization
Numerical Prediction of Cavitating Vortex Rope in a Draft Tube of a Francis Turbine with Standard and Calibrated Cavitation Model
Transient simulations of flow in a Francis turbine were performed with a goal to
predict pressure pulsation frequencies and amplitudes caused by rotating vortex rope at part
load operating regime. Simulations were done with the SAS SST turbulence model with
curvature correction on basic and refined computational meshes. Without cavitation modelling
too small values of frequency and amplitudes were obtained. With mesh refinement the
calculated amplitudes were a bit closer to the measured values, while the accuracy of predicted
frequency did not improve at all. Agreement between measured and numerical values was
significantly improved when cavitation was included in simulations. In addition, the predicted
value of the dominant frequency was slightly more accurate when, in the Zwart et al. cavitation
model, the default condensation and evaporation model constants were replaced with
previously calibrated ones
Satisfaction with Life Scale among adolescents and young adults in Portugal: extending evidence of construct validity
The paper presents three empirical studies designed to extend the test of the
construct validity of the Satisfaction With Life Scale (SWLS) among Portuguese students.
In the first study, the responses of 461 elementary and secondary education students were
submitted to a principal component analysis. A solution of one single factor was chosen, accounting for 55.7 % of the total variance, with Cronbach alpha coefficient and inter-item correlation above .70 and .20, respectively. The second study used a sample of 317
undergraduate students and registered a similar factor solution for SWLS (/pq = 0.99), which accounted for 65.6 % of the total variance (Cronbach alpha .89 and inter-item correlation above .20). A test–retest analysis registered coefficients of .70 (T2) and .77 (T3) and no significant statistically differences between T2, T3 and T1. The third study used a sample of 107 foster care youths from elementary and secondary education. Confirmatory factor analysis results indicate adequate fit indexes for the one-factor solution (v2/df = 2.70, GFI = .96, CFI = .96), which showed convergent validity, reliability and homogeneity. In conclusion, there is psychometric evidence for the one-factor structure of the SWLS in Portugal.FCTCOMPET