/* DATA DESCRIPTION: Citation: Zamani Asl, Mohammad Mehdi; Avila, Marc (2026): Dataset of direct numerical simulations of turbulent mixing in a T-shaped mixer for Reynolds number up to 2000, Schmidt number unity and laminar inlets [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.997505 (DOI registration in progress) Abstract: Despite its widespread use as a model configuration for investigating mixing processes in chemical engineering, the turbulent regime of the T-shaped mixer remains relatively unexplored, in contrast to its well-documented transitional behaviour. To address this gap, we performed direct numerical simulations at Reynolds numbers up to Re = 2000 with a Schmidt number of Sc = 1 with spectral-element solver Nek5000. The results reveal a streamwise evolution characterised by two distinct regions before the flow approaches a fully developed duct-flow state. In the vicinity of the junction, the dynamics are dominated by a jet-like structure that displays approximate self-similarity resembling that of transitional planar jets. Downstream of this region, turbulence undergoes a decay process in which turbulent kinetic energy, dissipation, and scalar variance exhibit power-law scaling. Interestingly, the velocity-related decay exponents are characteristic of turbulence confined within bounded domains, whereas scalar variance decays at a rate consistent with unbounded turbulent flows. This difference can be explained by the spatial development of the mixing process: although turbulent fluctuations have spread across the entire channel cross-section by the end of the jet region, scalar homogenisation continues to advance laterally from the channel centre toward the walls within the decay region. In addition, the mean scalar distribution retains an error-function shape in the transverse direction, reminiscent of laminar mixing. The resulting streamwise development of the mean mixing state is described using an effective diffusion coefficient that varies along the channel. This dataset provides all the post-processed data necessary to reproduce the figures in the manuscript (doi:10.1017/jfm.2026.12098). Further, original Nek5000 binary output files (.f) can be used to extract simulation data at arbitrary spatial coordinates within the T-mixer for the averaged TKE quantities and scalar variance. Instantaneous velocity and scalar fields of the simulations are provided that allow to restart all simulations in Nek5000. Keyword(s): turbulence simulation; turbulence theory; turbulent mixing Related to: Zamani Asl, Mohammad Mehdi; Avila, Marc (2026): Stages of turbulence generation and decay in a T-shaped mixer. Journal of Fluid Mechanics, 1044, A17, https://doi.org/10.1017/jfm.2026.12098 Parameter(s): Binary Object (Binary) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated Binary Object (File Size) [Bytes] (Binary (Size)) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated Figure (Fig) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated Title (Title) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated File name (File name) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated File format (File format) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated Description (Description) * PI: Zamani Asl, Mohammad Mehdi (https://orcid.org/0000-0002-1322-6258, mehdi.zamani@zarm.uni-bremen.de) * METHOD/DEVICE: Numerical simulated License: Creative Commons Attribution 4.0 International (CC-BY-4.0) (URI: https://creativecommons.org/licenses/by/4.0/) Status: Curation Level: Enhanced curation (URI: https://wiki.pangaea.de/wiki/Curation_levels) Size: 168 data points Files: All files referred to in data matrix can be downloaded in one go as ZIP or TAR (PANGAEA user account required). To download single files, use the filename from data matrix appended to "https://download.pangaea.de/dataset/997505/files/". */ Binary Binary (Size) [Bytes] Fig Title File name File format Description Fig2.zip 525.5 kBytes 2 Velocity colormap and profile Fig2.zip mat The file contains data of velocity at the inlet. It plots two figure. Figure (a) is colour map of the streamwise velocity at the inlet. Figure (b) is velocity profile at mid-height (z = 0). The dashed green line is from Schikarski et al (2019). Fig3.zip 42.4 kBytes 3 Convergence profiles Fig3.zip mat The file contains the average profile of Reynolds shear stress and r.m.s of velocity fluctuations. The code plots two figures. Figure (a) the average of Reynolds shear stress over successive 100 advective time unit intervals and over the full simulation time of 400 advective time units. Figure (b) relative errors of the Reynolds shear stress and r.m.s. of the velocity fluctuation as function of the averaging time (T). Fig4.zip 3.5 GBytes 4 Time-averaged velocity profiles Fig4.zip Nek5000 binary Binary Nek5000 files of averaged velocity fields of Re=2000 and Re=700 over 300 advectice time units. Python code in the file plots the (a-c) time-averaged streamwise velocity profiles at horizontal and (b–d) vertical mid-lines along the outlet at Re = 2000 and Re =700 over 300 advective time units, respectively. Fig5.zip 25.9 kBytes 5 Cross-sectionally averaged kinetic energy Fig5.zip mat Cross-sectionally averaged turbulent kinetic energy (k) for Re=2000 along the outlet. The code in the file plots the k along the outlet with three regions of the flow in shades of blue. Fig6and11.zip 10.2 MBytes 6 Cross sectional maps of k, P, mean scalar and scalar variance Fig6and11.zip mat Cross-sectional colour maps of kinetic energy, production , mean scalar and scalar variance for Re =2000 at x =2 and x=6. The code in the file plots the quadrant (quadrant averaging due to symmetry) of the four quantities at streamwise locations of x=2 and x=6. Fig7.zip 28.8 kBytes 7 Velocity and production profiles Fig7.zip mat (a) Velocity, (b) normalised velocity, (c) Pk and (d) normalised Pk profiles at Re = 2000 and several positions along the jet region . The dashed line jet profiles in (b)and(d) are from Gutmark & Wygnanski (1976) and Soligo et al. (2025), respectively. Fig8.zip 24.8 kBytes 8 Reynolds shear stress and velocity fluctuations profiles Fig8.zip mat (a) Reynolds shear stress, (b) streamwise, (c) horizontal and (d) vertical velocity fluctuations at Re =2000. The dotted and dashed lines are from Gutmark & Wygnanski (1976)andStanleyet al. (2002), respectively. Fig9.zip 27.9 kBytes 9 Velocity and production profiles Fig9.zip mat (a) Velocity, (b) normalised velocity, (c) Pk and (d) normalised Pk profiles at x = 2.5 and several Re at jet region . The dashed line jet profiles in (b)and(d) are from Gutmark & Wygnanski (1976) and Soligo et al. (2025), respectively. Fig10.zip 145 MBytes 10 Q-criterion Fig10.zip dat Q-criterion at the jet region. Vortex structures defined by iso-surfaces of Q criterion at 95% level in the jet region at Re =2000: The code in the file plots (a) three-dimensional view and (b) top view. The colouring is based on the streamwise direction. Fig12.zip 27 kBytes 12 Cross-sectionally averaged kinetic energy, dissipation and scalar variance Fig12.zip mat Evolution of the cross-sectionally averaged kinetic energy k, (b) dissipation εk and (c) scalar variance along the outlet at various Re. The code in the file plots this four quantities along the outlet. The inset in(a) shows v′ rms/u′ rms (green) and w′ rms/u′ rms (black) along the centreline for Re = 2000. The inset in (b)showscε =ε k−3/2 along the centreline. Fig13.zip 141.4 MBytes 13 Q-criterion Fig13.zip dat Q-criterion at the decay region. Vortex structures defined by iso-surfaces of Q criterion at 95% level in the decay region at Re =2000: The code in the file plots (a) three-dimensional view and (b) top view. The colouring is based on the streamwise direction. Fig14.zip 50.2 kBytes 14 Velocity , velocity fluctuations, production, dissipation and TKE fluxes profiles Fig14.zip mat Streamwise velocity profile (a), r.m.s. velocities (b) and production Pk, εk and sum of TKE fluxes Sk along the wall-normal direction (y = 0andx =18) (c). The dashed line represents the rectangular duct data with aspect ratio of 2 at Re =2000. (d) Cross-sectionally integrated Pk, εk and Sk along the outlet. Fig15.zip 4.6 MBytes 15 Cross sectional mean velocity magnitude and mean streamwise vorticity Fig15.zip mat Cross-sectional mean velocity magnitude and mean streamwise vorticity at x=18 for Re=2000. The code in the file plots the colormaps of these two quantities. Fig16and17.zip 4.1 MBytes 16 mean scalar, scalar profile, scalar integral mixing width, mixing thickness and effective diffusivity Fig16and17.zip mat (a) Spanwise colour map of mean scalar averaged in vertical direction (z) for Re=2000. (b) Scalar profiles at various streamwise locations of x=1.5, 3, 6, 9, 12 and 15 , with the corresponding error-function fits shown as solid lines. (c) Computed scalar integral mixing width for various Re. (d) Mixing thickness computed for various Re.(e) Computed Deff along the outlet. Figure (17) Scaling of the maximum effective diffusion coefficient with respect to Pe. Re700.zip 860.6 MBytes - Raw DNS output files (Nek5000) for Re700 Re700.zip Nek5000 binary Binary file of instantaneous fields of Re=700 case which can be used to restart the simulations in Nek5000. It contains the velocity, pressure and scalar field at t=75. Re1000.zip 1.1 GBytes - Raw DNS output files (Nek5000) for Re1000 Re1000.zip Nek5000 binary Binary file of instantaneous fields of Re=1000 case which can be used to restart the simulations in Nek5000. It contains the velocity, pressure and scalar field at t=97. Re1500.zip 1.4 GBytes - Raw DNS output files (Nek5000) for Re1500 Re1500.zip Nek5000 binary Binary file of instantaneous fields of Re=1500 case which can be used to restart the simulations in Nek5000. It contains the velocity, pressure and scalar field at t=69. Re2000.zip 2.8 GBytes - Raw DNS output files (Nek5000) for Re2000 Re2000.zip Nek5000 binary Binary file of instantaneous fields of Re=2000 case which can be used to restart the simulations in Nek5000. It contains the velocity, pressure and scalar field at t=22. conv.zip 3 GBytes - Raw DNS output files (Nek5000) of convection conv.zip Nek5000 binary Binary file containing the convection term of TKE in the whole T-mixer at Re=2000 averaged over 300 advective time units. eps.zip 2.7 GBytes - Raw DNS output files (Nek5000) of dissipation eps.zip Nek5000 binary Binary file containing the dissipation term of TKE in the whole T-mixer at Re=2000 averaged over 300 advective time units. pro.zip 3.1 GBytes - Raw DNS output files (Nek5000) of production pro.zip Nek5000 binary Binary file containing the production term of TKE in the whole T-mixer at Re=2000 averaged over 300 advective time units. prt.zip 3 GBytes - Raw DNS output files (Nek5000) of pressure transport prt.zip Nek5000 binary Binary file containing the pressure transport term of TKE in the whole T-mixer at Re=2000 averaged over 300 advective time units. ttt.zip 2.9 GBytes - Raw DNS output files (Nek5000) of turbulent transport ttt.zip Nek5000 binary Binary file containing the turbulent transport term of TKE in the whole T-mixer at Re=2000 averaged over 300 advective time units. vis.zip 3.1 GBytes - Raw DNS output files (Nek5000) of viscous diffusion vis.zip Nek5000 binary Binary file containing the viscous diffusion term of TKE in the whole T-mixer at Re=2000 averaged over 300 advective time units. scl.zip 2.7 GBytes - Raw DNS output files (Nek5000) of scalar variance scl.zip Nek5000 binary Binary file containing the scalar variance in the whole T-mixer at Re=2000 averaged over 300 advective time units. tau.zip 2.8 GBytes - Raw DNS output files (Nek5000) of Reynolds stress tau.zip Nek5000 binary Binary file containing the Reynolds shear stress in the whole T-mixer at Re=2000 averaged over 300 advective time units. rms.zip 2.6 GBytes - Raw DNS output files (Nek5000) of velocity fluctuations rms.zip Nek5000 binary Binary file containing the velocity r.m.s in the whole T-mixer at Re=2000 averaged over 300 advective time units. tke.zip 2.7 GBytes - Raw DNS output files (Nek5000) of kinetic energy tke.zip Nek5000 binary Binary file containing the Turbulent kinetic energy in the whole T-mixer at Re=2000 averaged over 300 advective time units.