1,720,966 research outputs found
Generation of upper trailing counter-rotating vortices of a sonic jet in a supersonic crossflow: Generation of upper trailing CRVs of transverse sonic jet in a supersonic crossflow at Ma=2.7
No full textDirect numerical simulations were conducted to investigate physical structures of a transverse sonic air jet injected into a supersonic air crossflow at a Mach number of 2.7. Simulations were run for two different jet-to-crossflow momentum flux ratios (J) of 1.85 and 5.5. The main averaged flow features around the transverse jet, such as major counter rotating vortices (CRVs) and trailing CRVs (TCRVs) were captured. The major CRVs form in the lateral portion of the jet plume and absorb other induced trailing vortices downstream of the jet plume. Upper trailing CRVs form above the major CRVs downstream of the jet barrel shock. The streamline analysis indicates that the upper trailing CRVs are related to the Mach disk. As the streamlines penetrate the lateral side of Mach disk where a strong shear condition exists, the baroclinic torque induces upper vorticities in the opposite rotating direction against the major CRVs. Downstream of the Mach disk, the baroclinic vorticity production along the streamlines tends to approach zero, which means no more torque is pumped into the farfield and the upper TCRVs are merged into the major CRVs by their suction
Data for "Formation of surface trailing counter-rotating vortex pairs downstream of a sonic jet in a supersonic crossflow"
No full textData set for Paper "Formation of surface trailing counter-rotating vortex pairs downstream of a sonic jet in a supersonic crossflow" published in Journal of Fluid Mechanics.
The files are named by the figure numbers, e.g. figure3a.lpk, together with figure3a.dat, contain all data for Figure 3(a) in the paper, and can be opened by Tecplot. </span
Dataset for 'Turbulence structures and statistics of a supersonic turbulent boundary layer subjected to concave surface curvature'
No full textThis dataset contains data files for the paper
"Turbulence structures and statistics of a supersonic turbulent boundary layer subjected to concave surface curvature" by Sun, Mingbo; Sandham, Neil; Hu, Zhiwei published by Journal of Fluid Mechanics.
They can be opened in Tecplot</span
Recovery of a supersonic turbulent boundary layer after an expansion corner
No full textSupersonic turbulent flows at Mach 2.7 over expansion corners with deflection angles of 0° (flat plate), 2° and 4° have been studied using direct numerical simulation. Distribution of the skin friction, pressure, velocity and the boundary layer growth show that the turbulent boundary layer experiences a recovery from a non-equilibrium to an equilibrium state downstream of the expansion corner. Analysis of velocity profiles indicates that the streamwise velocity undergoes a reduction in the near-wall region even though the velocity in the core part of the boundary layer is accelerated after the expansion corner. Growth of the boundary layer was evaluated and a higher shape factor was found in the expansion cases. Turbulence was found to be suppressed downstream of the corner, and throughout the recovery region, even though turbulence is regenerated in the near-wall region. The expansion ramp increases the near wall streak spacing compared to a flat plate and turbulent kinetic energy profiles and budgets exhibit a characteristic two-layer structure. Near-wall turbulence recovers to the equilibrium more quickly in the inner layer than in the outer layer due to a balance between the local production and dissipation. The two-layer structure is due to the history effect of the turbulence decay in the outer part of the boundary layer in the vicinity downstream of the expansion corner, which blocks the momentum and energy exchange between the inner layer and the main stream
Dataset for Recovery of a supersonic turbulent boundary layer after an expansion corner
No full textData set for Physics of Fluids paper "Recovery of a supersonic turbulent boundary layer after an expansion corner"</span
Mixing in nearwall regions downstream of a sonic jet in a supersonic crossflow at Mach 2.7
No full textThe mixing status downstream of a transverse sonic jet in a supersonic crossflow at a Mach number of 2.7 was studied. Direct numerical simulations were performed to investigate the transport of a passive scalar of jet fluid for jet-to-cross-flow momentum flux ratios (denoted as J) of 1.85 and 5.5. Results showed that a counter-rotating vortex pair (CVP) with two branches generates in the jet nearfield, grows, and breaks into small eddies in the farfield, which enhances the local mixing. A nearwall region in the jet lee between the CVP branches is identified to have a low mass fraction of the jet fluid and this region expands as J increases. Analysis of the streamlines originating from the jet orifice and the crossflow suggests that the jet fluid in the downstream nearwall region is entrained by the lateral crossflow upstream of the jet, which travels around the jet and mixes with the injectants downstream of the jet. Higher J leads to a lower mass fraction of the jet fluid in the nearwall region of the jet nearfield, but produces a higher mass fraction in the nearwall region of the farfield. A three-dimensional schematic of the jet wakes is presented and explains the formation of the nearwall low mass fraction zone in the jet nearfield.</p
The amplification of large-scale motion in a supersonic concave turbulent boundary layer and its impact on the mean and statistical properties
No full textDirect numerical simulation is conducted to uncover the response of a supersonic turbulent boundary layer to streamwise concave curvature and the related physical mechanisms at a Mach number of 2.95. Streamwise variations of mean flow properties, turbulence statistics and turbulent structures are analysed. A method to define the boundary layer thickness based on the principal strain rate is proposed, which is applicable for boundary layers subjected to wall-normal pressure and velocity gradients. While the wall friction grows with the wall turning, the friction velocity decreases. A logarithmic region with constant slope exists in the concave boundary layer. However, with smaller slope, it is located lower than that of the flat boundary layer. Streamwise varying trends of the velocity and the principal strain rate within different wall-normal regions are different. The turbulence level is promoted by the concave curvature. Due to the increased turbulence generation in the outer layer, secondary bumps are noted in the profiles of streamwise and spanwise turbulence intensity. Peak positions in profiles of wall-normal turbulence intensity and Reynolds shear stress are pushed outward because of the same reason. Attributed to the Görtler instability, the streamwise extended vortices within the hairpin packets are intensified and more vortices are generated. Through accumulations of these vortices with a similar sense of rotation, large-scale streamwise roll cells are formed. Originated from the very large-scale motions and by promoting the ejection, sweep and spanwise events, the formation of large-scale streamwise roll cells is the physical cause of the alterations of the mean properties and turbulence statistics. The roll cells further give rise to the vortex generation. The large number of hairpin vortices formed in the near-wall region lead to the improved wall-normal correlation of turbulence in the concave boundary layer
Detonation stabilization in supersonic flow: effects of suction boundaries
No full textIn the present work, detonation stabilization in the supersonic flow is numerically investigated in the straight channel with suction boundaries. The two-dimensional reactive Navier–Stokes equations, together with a one-step reaction model, are solved using a second-order-accurate finite volume method solver based on the Structured Adaptive Mesh Refinement framework. The results show that, compared with one jet initiation, detonation initiation can be achieved in a shorter distance using two hot jets subject to the equal total width of the jets. When the suction slots are turned on, the overdriven detonation undergoes a gradual attenuation along with the weakening of the transverse waves, hence leading to dynamic detonation stabilization in the supersonic flow. When the suction slots are closer to the detonation front, the forward propagation of the detonation in the supersonic flow can be more effectively prohibited, implying that the suction slots should be distributed as close as possible to the detonation front in order to realize the maximal suction effect using the minimal suction slots
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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