TY - GEN A1 - Barzantny, Marcel A1 - Hamede, Mohammed Hussein A1 - Majchrzyk, Michał A1 - Merbold, Sebastian A1 - Egbers, Christoph A1 - Kostowski, Wojciech T1 - Experimental investigation of the flow characteristics driving the Ranque–Hilsch phenomenon T2 - International journal of heat and mass transfer N2 - The Ranque–Hilsch vortex tube (RHVT) is a device that separates a pressurized inlet stream into two decompressed streams of different temperature, flowing to the so-called hot and cold outlets. In this study, the flow structures within the vortex tube were examined qualitatively. The examination considered both compressible and incompressible fluids, using pressurized air and water as working fluids. A parametric study was conducted, in which the fluid inlet pressure and the vortex tube length were varied. Three tubes, with the same diameter but differing lengths (100, 180, and 240 mm) were utilized. The flow inside the tube was investigated using a flow visualization technique, which was employed in a variety of configurations and setups contingent on the specific fluid conditions under examination. The visualization process required the use of aerosol injection in the case of air, and kalliroscope particles in the case of water investigation. The research enabled the visualization of the flow structure within the vortex tube, thereby significantly advancing the comprehension of the underlying physical processes. The findings of the experimental research demonstrated the existence of phenomena of considerable scientific value. The internal vortex and its spatial and temporal structure observed in the RHVT were consistent with literature data. This was achieved despite the so-far established consensus that this type of research is challenging and not entirely reliable. In the course of water-based investigation, the cavitation phenomenon was observed in the vicinity of the internal vortex. This discovery is likely to be the first of its kind and may contribute significantly to the advancement of research on the Ranque–Hilsch phenomenon. KW - Ranque–Hilsch phenomenon KW - Vortex tube KW - Flow visualization KW - Cavitation Y1 - 2025 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2025.127543 SN - 0017-9310 VL - 253 SP - 1 EP - 14 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Zanoun, El-Sayed A1 - Bauer, Christian A1 - Wagner, Claus A1 - Durst, Franz A1 - Egbers, Christoph A1 - Bellani, Gabriele A1 - Talamelli, Alessandro T1 - Cross-validation of numerical and experimental data in turbulent pipe flow with new scaling correlations T2 - Journal of turbulence N2 - The dependence of turbulence statistics and wall friction on Reynolds number in fully developed turbulent pipe flow remains a fundamental subject in fluid mechanics. This paper cross-validates experimental and numerical results, focusing on the scaling of turbulence statistics at the pipe centerline and across the inner-outer flow region. Pipe flow experiments were reviewed for friction Reynolds numbers 810≤Re𝜏≤55×103, where Re𝜏=𝑢𝜏⁢𝑅/𝜈, 𝑢𝜏 is the wall friction velocity, 𝑅 the pipe radius, and 𝜈 the kinematic viscosity. Complementary DNS data for 180≤Re𝜏≤2880 provide detailed insight into near-wall turbulence. A novel friction correlation, Re𝜏=0.048Re0.923 c is introduced, predicting pipe-wall friction across a wide range of Re𝑐 with accuracy better than ±2.06%, where Re𝑐 is the Reynolds number based on the centerline streamwise mean velocity component 𝑈zc. This correlation enables reliable friction estimates from centerline single-point measurements or DNS data without requiring near-wall or streamwise pressure-gradient information and is validated by consistent agreement with both experiments and DNS. The monotonic decrease in centerline turbulence intensity ⟨𝑢′𝑧2⟩1/2/𝑈zc with increasing Re𝑐 is explained using the streamwise mean momentum equation. Finally, azimuthal spatial filtering of DNS data highlights the limitations of hot-wire resolution near the wall. For Re𝜏≥2880, higher-order experimental statistics agree well with DNS for 𝑦+≥30 and into the logarithmic region, with both datasets equally well described by logarithmic or power-law correlations, while near-wall discrepancies remain due to resolution limits. KW - Pipe flow KW - Turbulence statistics KW - DNS KW - Experiments Y1 - 2025 U6 - https://doi.org/10.1080/14685248.2025.2560314 SP - 1 EP - 22 PB - Taylor & Francis CY - London ER - TY - GEN A1 - Hamede, Mohammed Hussein A1 - Sliavin, Yaraslau A1 - Motuz, Vasyl A1 - Egbers, Christoph T1 - The effect of flow initial conditions and geometry on the saturation of the thermo-electrohydrodynamic instability within microgravity conditions T2 - Physics of fluids N2 - The present study investigates the thermo-electrohydrodynamic-induced convection in a dielectric fluid confined between two concentric differentially heated cylinders under microgravity conditions through experimental means. The experiments were conducted during parabolic flight campaigns. In the present study, our primary focus was on the saturation of perturbations induced by thermo-electrohydrodynamic instability. The effect of initial flow conditions on perturbation growth rates is examined when entering the microgravity phase. Furthermore, a series of experimental setups with varied lengths and aspect ratios were considered to investigate the impact of geometry on flow behavior. The present study quantitatively investigated the flow using particle image velocimetry in the meridional and radial–azimuthal planes. Furthermore, direct measurements were taken of the global response of the flow, in this case heat transfer, using a heat flux sensor attached to the outer cylinder wall. KW - Heat transfer KW - Electrostatics KW - Microgravity KW - Dielectric materials KW - Fluid instabilities KW - Fluid dynamics KW - Flow instabilities KW - Flow visualization Y1 - 2025 U6 - https://doi.org/10.1063/5.0287547 VL - 37 IS - 9 SP - 1 EP - 10 PB - AIP Publishing CY - College Park, Maryland ER -