Yue Wang

The effect of slit injection of a surfactant solution on the flow characteristics of the boundary layer on a flat plate in low Reynolds number (Re<20 000) flows is studied experimentally. The velocity distribution at 10 and 20 times the injection slit width (Lc) away from the slit was measured by particle image velocimetry (PIV). The effects of the concentration and the injection flow rate of the polymeric solution on the flow characteristics of the boundary layer at low Reynolds numbers were discussed, through the comparison of the local velocity and velocity fluctuation at different surfactant concentrations and the injection velocity at the slit. Results show that within the studied concentration and injection velocity range, the drag reduction is greatest at a polymer concentration of 50 ppm. As the concentration increases, the drag reduction effect gradually decreases. Furthermore, the injection of the polymer solution has a certain suppressive effect on the turbulent kinetic energy of the boundary layer, especially the velocity fluctuations perpendicular to the wall. Appropriate injection concentrations can also suppress local Reynolds shear stresses in the boundary layer.

The Rayleigh–Bénard convection (RBC) with viscoelastic fluids has captured wide attention in the past decades, caused by its ubiquitous uses in the heat transfer process. However, the numerical technique for simulating the viscoelastic fluid flows developed slowly until recent years because of the numerical instability raised by the hyperbolic characteristics of the viscoelastic constitutive equation. In the present work, a novel numerical scheme was developed to simulate the three-dimension (3D) RBC with viscoelastic fluids, where the quasi-linear treatment was applied to the hyperbolic terms of the momentum equation and the viscoelastic constitutive equation. The in-house solver was also optimized in the aspect of time cost. The results show that the critical value of convection onset in 3D is near to that in the two-dimension (2D); however, the flow pattern displays the wave characteristics in the horizontal direction. The viscoelastic kinetic energy budget of oscillating convection in 3D still conforms to the energy transport law of that in 2D [Zheng et al., Phys. Rev. Fluids 8, 023303 (2023)].

To improve the performance of a high-pressure refueling liquid oxy-kerosene engine, the influence of drag-reducing additive on the heat transfer characteristics in the supercritical flow of kerosene in a microchannel for regenerative cooling is explored. The finite-volume CFD numerical simulation method is applied using the RNG k-ε turbulence model and enhanced wall function. The current work faithfully represents the effect of the drag-reducing additive in kerosene through numerical calculations by combining a 10-component model for the physical properties of the kerosene and the Carreau non-Newtonian fluid constitutive model from rheological measurements. Results suggest that the 10-component kerosene surrogate can describe the supercritical physical properties of kerosene. The inlet temperature, inlet velocity, and the heat flux on the channel wall are driving factors for the supercritical kerosene flow and heat transfer characteristics. The pressure influence on the heat transfer is negligible. With polymer additives, the loss in pressure drop and heat transfer performance of supercritical kerosene flow decrease 46.8% and 37.5% respectively. The enhancement of engine thrust caused by reduction in pressure drop is an attractive improvement of concern.