On the impact of the aspect ratio on the formation of large-Scale structures in turbulent mixed convection in a cuboidal sample. - In: International journal of heat and fluid flow, ISSN 1879-2278, Bd. 76 (2019), S. 231-241
https://doi.org/10.1016/j.ijheatfluidflow.2019.01.004
Buoyancy-induced effects on large-scale motions in differentially heated vertical channel flows studied in direct numerical simulations. - In: International journal of heat and fluid flow, ISSN 1879-2278, Bd. 75 (2019), S. 14-26
Direct numerical simulations of turbulent convection in a differentially heated vertical channel flow with Prandtl number Pr = 0.71 are conducted with a fourth-order accurate finite volume method for a bulk Reynolds number Reb = 4328 and three Grashof numbers Gr [Element] {0, 6.4 &hahog; 105, 9.5 &hahog; 105}. The discussion of instantaneous flow field snapshots, first- and second-order moments, budget equations, power density spectra and quadrant analyses shows that the turbulent velocity fluctuations are attenuated in the aiding flow and enhanced in the opposing flow. In contrast, temperature fluctuations are attenuated in the opposing flow and enhanced in the aiding flow. The analyses further reveal that the low-momentum flow structures in the aiding flow are warmer than the highmomentum flow structures and vice versa in the opposing flow. Due to their different temperatures, buoyancy accelerates and decelerates the flow structures differently, which leads to reduced and increased pressure and shear fluctuations in the aiding and opposing flow. Thus, the redistribution of turbulent velocity fluctuations is lower in the aiding flow and higher in the opposing flow. The Reynolds shear stresses are consequently decreased in the former and increased in the latter, influencing the production of streamwise velocity fluctuations accordingly. In summary, the discussed physical mechanisms underline the indirect effect of buoyancy on the turbulent velocity fluctuations.
https://doi.org/10.1016/j.ijheatfluidflow.2018.09.005
Temperature dependence of heat and mass transfer in a forced convective duct flow with and without condensation on one wall. - In: 5th International Conference on Experimental Fluid Mechanics, (2018), S. 39-44
https://doi.org/10.18726/2018_2
New results in numerical and experimental fluid mechanics XI : contributions to the 20th STAB/DGLR Symposium Braunschweig, Germany, 2016. - Cham : Springer, 2018. - Online-Ressource (xv, 767 Seiten). - (Notes on numerical fluid mechanics and multidisciplinary design ; 136) ISBN 978-3-319-64519-3
https://doi.org/10.1007/978-3-319-64519-3
Numerical simulation of the sound generation and the sound propagation from air intakes in an aircraft cabin. - In: New results in numerical and experimental fluid mechanics XI, (2018), S. 623-633
https://doi.org/10.1007/978-3-319-64519-3_56
Direct numerical simulation of convective channel flow with temperature and concentration gradients. - In: New results in numerical and experimental fluid mechanics XI, (2018), S. 445-453
https://doi.org/10.1007/978-3-319-64519-3_40
Simulating pass-by noise of vehicles - comparison of a ray tracing model using simplified geometrical building models with measurement. - In: Taming noise and moving quiet, (2018), S. 135-145
Temperature profiles measurements in turbulent Rayleigh-Bénard convection by optical fibre system at the Barrel of IImenau. - In: EFM17 - Experimental Fluid Mechanics 2017, (2018), 02020, S. 1-6
https://doi.org/10.1051/epjconf/201818002020
Experimental study of the global flow-state transformation in a rectangular Rayleigh-Bénard sample. - In: International journal of heat and mass transfer, ISSN 1879-2189, Bd. 126 (2018), Part A (Nov.), Seite 1333-1346
Large-scale flow structures were measured in a rectangular Rayleigh-Bénard sample of equal length and height of 10 cm and a depth of 2.5 cm. The working fluid was water at a Prandtl number of Pr = 6.9. Aiming to capture flow structures to their full extent and throughout the entire sample, the threedimensional (3D) Lagrangian measurement technique 3D-Particle Tracking Velocimetry (3D-PTV) was employed. The study provided direct confirmation that the global mean flow field changes significantly in dependence of the Rayleigh number Ra within the investigated range of 2.1 &hahog; 10^6 ≤ Ra ≤ 4.5 &hahog; 10^8. Several distinguishable flow states were observed in the laminar-turbulent transition regime complementing the well-known mean wind. A two-dimensional (2D)-mode decomposition revealed a breakdown of the mean wind during the transition phase and its new formation in the turbulent regime. Further, the global distribution of magnitudes of the instantaneous velocity fields was used to extract characteristic velocities in the flow field. It was shown, that the Reynolds-number-dependent scaling law Re ˜ Ra^y can be unambiguously determined by means of directly measured Lagrangian velocities, since the same scaling behavior holds true for all chosen reference velocities. In this context, using the product of a polynomial and an exponential function, the global velocity distribution was described analytically in dependence of Ra and four independent fit parameters in the sub-range 2.8 &hahog; 10^7 ≤ Ra ≤ 4.5 &hahog; 10^8.
https://doi.org/10.1016/j.ijheatmasstransfer.2018.05.097
Assessment of the mesh refinement influence on the computed flow-fields about a model train in comparison with wind tunnel measurements. - In: Journal of wind engineering and industrial aerodynamics, Bd. 179 (2018), S. 102-117
A consistent mesh refinement study, relating to the prediction of aerodynamic forces about an experimentally validated reference train geometry, is presented in this paper. The flow about a high-speed train has a multi-scale character which poses challenges for the design of computationally effective meshes. The purpose of this study is to assist in the development of guidelines for effective drag prediction of high-speed trains using numerical simulation. These guidelines should assist CFD practitioners by identifying the regions of the mesh that are critical for the correct estimation of drag as well as providing information on appropriate mesh characteristics, such as volume and surface element length scales. Numerical assessments are validated against an experimental drag measurement program and the extent to which RANS is sufficiently predictive for industrial design is discussed. The results obtained in the work suggest that the mesh about the train nose is essential for the proper assessment of the aerodynamic drag acting on the vehicle.
https://doi.org/10.1016/j.jweia.2018.05.005