Experimental investigation of liquid film cooling in hypersonic flow

Abstract

ARTICLES YOU MAY BE INTERESTED INHigh-enthalpy models for boundary-layer stability and transition Physics of Fluids 31, 044101 (2019); https://doi.org/10.1063/1.5084235Numerical study of the shear-thinning effect on the interaction between a normal shock wave and a cylindrical liquid column Physics of Fluids 31, 043101 (2019); https://doi. ABSTRACTFilm cooling is generally considered as a promising active cooling technology for developing thermal protection systems of hypersonic vehicles; however, most of experimental and numerical studies of film cooling mainly concentrated on gaseous film cooling. Since the phase change of liquid coolants can absorb a large amount of latent heat, liquid film cooling should have more potential advantages, especially for severe environments accompanied by hypersonic flight. To address this issue, the film cooling using water as a coolant was experimentally investigated in hypersonic flow. Experiments were carried out in a detonation tunnel, at a hypersonic Mach number of 6 using a 25 ○ apex-angle wedge. Characteristic physical quantities, such as surface temperature rise, shock wave structure, film thickness, and cover area, are measured by thermocouples, schlieren, and a specially devised liquid film measurement system. The experimental results verify that the liquid film cooling is feasible in hypersonic flow and also indicate that it is featured with maintaining aerodynamic performances due to the weak effect on the main flow caused by coolant injection. Inspired by these results, liquid film flow characteristics and its influencing factors including mass flow rate, dynamic pressure, coolant injection direction, and surface tension are investigated to guide the design of a thermal protection system. Published under license by AIP Publishing. https://doi.Published under license by AIP Publishing FIG. 15. Effects of the coolant injection direction on the liquid film thickness and coverage area width. (a) θ = 0 ○ , (b) θ = 30 ○ , (c) θ = 60 ○ , and (d) cover area width.

Evaporation of Three-Dimensional Wavy Liquid Film Entrained by Turbulent Gas Flow

“…Since the cusp is the origin of a ligament producing droplets downstream, the cusp volume approximately coincides with total droplet volume detaching from the cusp. We derive < as discussed later, thus, the cross-sectional area of the conical cusp corresponds to 2…”

“…of a thin liquid film extending on a wall exposed to a fast gas flow is a general thermo-fluid issue in many practical situations, such as film-cooling technology [1][2][3], icing on aircraft wings [4][5][6], and drying of paints and cleaning solutions [7]. Past and recent studies including quantitative measurements [5,[8][9][10][11][12][13][14][15] provide a scenario that the turbulent gas flows over the initially smooth film, soon drives the film with complex wavy structures by Kelvin-Helmholtz (KH) instability as a roll wave, accelerates the wave crests producing transverse wave by Rayleigh-Taylor (RT) instability as a ripple wave, stretches ligaments, and eventually entrains droplets disintegrated by Plateau-Rayleigh instability, all in a sequential fashion.…”

“…For a liquid rocket engine combustion chamber employing the film cooling technique [1,2,7,19,20], minimizing the coolant flow rate is desired to improve the performance of characteristic velocity and specific impulse [3,19,21] with achieving the sufficient heat resistance. Liquid fuel jets are often ejected on the inner surface of the combustion chamber in a bipropellant thruster below the critical pressure of propellants, followed by the propagating liquid film covering the wall.…”