Hydroacoustic noise from different geometries

Turbulent flow around bluff bodies generates pressure fluctuations which propagate as acoustic waves. Differences in the shape of a body can affect frequencies and amplitudes of the propagating pressure signals. In the present work three elementary geometries (sphere, cube and prolate spheroid), immersed in a uniform water flow, are examined in order to analyze the differences of the resulting hydroacoustic fields. The turbulent flow at ReA = 4430 (based on the cross-sectional area of the bodies) is reproduced through wall-resolving Large-Eddy Simulation and the hydroacoustic far-field is analyzed by adopting the Ffowcs Williams and Hawkings analogy. The quadrupole term of the acoustic equation is first reformulated in the convective form and then solved through direct computation of the volume integrals. This procedure is found possible in hydrodynamics where the speed of sound is very large and the flow velocities are small. In spite of the fact that the frontal section of the bodies has the same area, the analysis shows that a streamlined body is able to produce a pressure signal one order of magnitude lower than that generated by a bluff geometry. The separate analysis of the loading noise and of the quadrupole one has shown that the former is larger than the latter in case of 3D-shaped bluff body (sphere and cube), whereas the opposite is true in case of a streamlined body. A preliminary analysis between the case of an elongated square cylinder and a cube, shows that the persistence of a two-dimensionally shaped wake when compared to a three-dimensional one contributes to increase the quadrupole part of the radiated noise

Detection of SF3B1 p.Lys700Glu Mutation by PNA-PCR Clamping in Myelodysplastic Syndromes and Myeloproliferative Neoplasms

Mutations in SF3B1 are found in 20% of myelodysplastic syndromes and 5–10% of myeloproliferative neoplasms, where they are considered important for diagnosis and therapy decisions. Sanger sequencing and NGS are the currently available methods to identify SF3B1 mutations, but both are time-consuming and expensive techniques that are not practicable in most small-/medium-sized laboratories. To identify the most frequent SF3B1 mutation, p.Lys700Glu, we developed a novel fast and cheap assay based on PNA-PCR clamping. After setting the optimal PCR conditions, the limit of detection of PNA-PCR clamping was evaluated, and the method allowed up to 0.1% of mutated SF3B1 to be identified. Successively, PNA-PCR clamping and Sanger sequencing were used to blind test 90 DNA from patients affected by myelodysplastic syndromes and myeloproliferative neoplasms for the SF3B1 p.Lys700Glu mutation. PNA-PCR clamping and Sanger sequencing congruently identified 75 negative and 13 positive patients. Two patients identified as positive by PNA-PCR clamping were missed by Sanger analysis. The discordant samples were analyzed by NGS, which confirmed the PNA-PCR clamping result, indicating that these samples contained the SF3B1 p.Lys700Glu mutation. This approach could easily increase the characterization of myelodysplastic syndromes and myeloproliferative neoplasms in small-/medium-sized laboratories, and guide patients towards more appropriate therapy

Direct Numerical Simulation of Turbulent Heat Transfer Modulation in Micro-Dispersed Channel Flow

The object of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano- particles. We run Direct Numerical Simulation (DNS) for hydrodynamically fully-developed, thermally-developing turbulent channel flow at shear Reynolds number Re=150 and Prandtl number Pr=3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined.Comment: Pages: 305-32

Assessment of methodologies for the solution of the Ffowcs Williams and Hawkings equation using LES of incompressible single-phase flow around a finite-size square cylinder

The acoustic analogy represents a powerful tool for the prediction of noise generated by the interaction between the flow and a moving body. It is based on decoupling the acoustic problem from the fluid dynamic one: the velocity and pressure fields, obtained through a separate numerical simulation, are used as source terms in an inhomogeneous wave equation whose solution reconstructs the noise in the far field. When the method is based on the fundamental Ffowcs Williams and Hawkings (FW-H) equation, different solving methodologies may be adopted. The present work considers the original FW-H equation and gives the advective formulation of the volume integral terms. The results are compared with those obtained with the Curle and porous formulations. To account for volume integrals, the assumption of compact noise source is needed. This assumption is common in literature, however, in the present work, a dimensional analysis is proposed, in order to indicate in a rigorous way the cases in which the compressibility delays can be avoided. The dimensional analysis is tested in the case of an acoustic monopole field. Successively, the FW-H porous formulation is compared with the original FW-H equation in the case of an irrotational advected vortex. This example puts in evidence the different response of the two methods in the case of a vortex crossing the acoustic domain. Then, different solution strategies of the FW-H are evaluated using a fluid dynamic dataset obtained through large eddy simulation of a turbulent flow around a finite-length cylinder with square section. The analysis allows to point out the strengths and drawback of the different techniques and to achieve, through the comparison of the different solutions, an accurate understanding of the noise source mechanisms taking place in the flow. Finally, a mixed procedure, merging the advantages of the porous formulation with the direct evaluation of the volume integral terms is proposed. It may be used in presence of significant time delays. Overall, the present study is oriented to the analysis of very low Mach number flows, although the complete porous method might be applicable in a more general framework. This aspect will require additional research in the future

Assessment of solution algorithms for LES of turbulent flows using OpenFoam

We validate and test two algorithms for the time integration of the Boussinesq form of the Navier\u2014Stokes equations within the Large Eddy Simulation (LES) methodology for turbulent flows. The algorithms are implemented in the OpenFOAM framework. From one side, we have implemented an energy-conserving incremental-pressure Runge\u2013Kutta (RK4) projection method for the solution of the Navier\u2013Stokes equations together with a dynamic Lagrangian mixed model for momentum and scalar subgrid-scale (SGS) fluxes; from the other side we revisit the PISO algorithm present in OpenFOAM (pisoFoam) in conjunction with the dynamic eddy-viscosity model for SGS momentum fluxes and a Reynolds Analogy for the scalar SGS fluxes, and used for the study of turbulent channel flows and buoyancy-driven flows. In both cases the validity of the anisotropic filter function, suited for non-homogeneous hexahedral meshes, has been studied and proven to be useful for industrial LES. Preliminary tests on energy-conservation properties of the algorithms studied (without the inclusion of the subgrid-scale models) show the superiority of RK4 over pisoFoam, which exhibits dissipative features. We carried out additional tests for wall-bounded channel flow and for Rayleigh\u2013B\ue8nard convection in the turbulent regime, by running LES using both algorithms. Results show the RK4 algorithm together with the dynamic Lagrangian mixed model gives better results in the cases analyzed for both first- and second-order statistics. On the other hand, the dissipative features of pisoFoam detected in the previous tests reflect in a less accurate evaluation of the statistics of the turbulent field, although the presence of the subgrid-scale model improves the quality of the results compared to a correspondent coarse direct numerical simulation. In case of Rayleigh\u2013B\ue9nard convection, the results of pisoFoam improve with increasing values of Rayleigh number, and this may be attributed to the Reynolds Analogy used for the subgrid-scale temperature fluxes. Finally, we point out that the present analysis holds for hexahedral meshes. More research is need for extension of the methods proposed to general unstructured grids