Angeles Malaspina, Moisés E.

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    Unsteady cavitation prediction for turbulent waterhammer flow
    (2015) Angeles Malaspina, Moisés E.; Silva Araya, Walter; College of Engineering; Rivera Santos, Jorge; Zapata López, Raúl E.; Segarra García, Rafael; Department of Civil Engineering; Rosario, Héctor
    The waterhammer phenomenon is an important factor to consider during the pipe system design in order to avoid pipe failure due to suddenly increased pressure. Many accidents, even with loss of life, are illustrated in literature. These pipe failures also can occur when vapor cavities collapse causing large pressure increases. In the classical cavitating waterhammer flow, the vapor cavity is considered as an internal boundary condition at a fixed pipe location. Several other one‐dimensional models were developed considering vapor bubble effects on the pressure wave propagation, but considering a constant friction term without interaction between the turbulent structure and the vapor bubbles. In this current research, the 𝘕𝘢𝘷𝘪𝘦𝘳‐𝘚𝘵𝘰𝘬𝘦𝘴 and the 𝘙𝘦𝘺𝘯𝘰𝘭𝘥𝘴‐𝘢𝘷𝘦𝘳𝘢𝘨𝘦𝘥 𝘕𝘢𝘷𝘪𝘦𝘳‐𝘚𝘵𝘰𝘬𝘦𝘴 equations are solved for single phase flow. The liquid compressibility is considered by solving the 𝘍𝘢𝘷𝘳𝘦‐𝘢𝘷𝘦𝘳𝘢𝘨𝘦𝘥 𝘕𝘢𝘷𝘪𝘦𝘳‐𝘚𝘵𝘰𝘬𝘦𝘴 equations. The two‐dimensional turbulent flow is solved using the turbulent models of 𝘒‐ ε, 𝘒‐ω and Low Reynolds 𝘒‐ω. Cavitation is modeled as a two‐phase homogeneous mixture flow by using the Shingal model and interconnecting the turbulent kinetic energy with the inside pressure vapor bubble. The proposed model in this research was compared with analytical and experimental data. Pulsatile laminar flow is very well predicted. The model is capable of capturing reverse velocities, and pressure-velocity phase lag for unsteady oscillatory under laminar and turbulent flow. The waterhammer flow conditions with a rapid valve closure for laminar flow and transition to rough pipe in turbulent flow are very well predicted but with some under prediction of the pressure peaks. Numerical simulation for cavitating waterhammer flow predicts very well the pressure wave and is able to define the regions where cavitation is developed.
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    An assessment of future Caribbean climate change using "business as usual" scenario by coupling GCM data & RAMS
    (2005) Angeles Malaspina, Moisés E.; González-Cruz, Jorge E.; College of Engineering; Benítez, Jaime; Pandya, Vikram; Williams, Robin; Department of Mechanical Engineering; Ramírez Beltran, Nazario
    The Caribbean rainfall season has a bimodal nature, which is divided in the Early Rainfall Season (ERS) and Late Rainfall Season (LRS). To carry out the long-term average conditions Caribbean season analysis, the National Center for Environmental Prediction (NCEP) reanalysis data, the Xie-Arkin precipitation and the Reynolds-Smith Sea Surface Temperature (SST) observed data were used. The Parallel Climate Model (PCM) is evaluated to determine its ability to predict the Caribbean climatology. As a result, PCM under predicts the SSTs, which along a cold advection cause a lower rain production than the observed climatology. The future Caribbean climatological condition simulated by PCM shows a future warming of up to ~10 C along with an increase of the rain production during the Caribbean seasons. RAMS was coupled with PCM to assess the dynamical downscale technique. The PCM data used in RAMS as initial conditions has very low SSTs and a stable atmosphere cutting off the vertical convection. To avoid the deviations generated by the PCM output when it is used in RAMS, the 1998 observed data plus the PCM atmospheric variables difference between the years 2048 and 1998 is taken as initial conditions to RAMS. The synoptic scale simulated by RAMS shows a close behavior to the simulated by PCM during the dry season and LRS, while the mesoscale rainfall is strongly influenced by the land dry areas computed in the parent grid.