Visualization of Coolant Liquid Film Dynamics in Hypergolic Bipropellant Thruster

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

“…For rocket engines in general, it is known that ∝ and ∝ . Reliability of the experimental data is previously confirmed [3].…”

“…Now let us solve the heat transfer problem in a pipe. Inside a combustion chamber, a liquid film temperature on a wall promptly becomes the saturation temperature as convinced by Fujii et al [3] The wall temperature within the area covered by the liquid film is approximately equal to [39]. We treat the wall as adiabatic condition and consider a heat source of convective heat transfer from the turbulent hot gas.…”

“…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.…”

“…Experimental studies inside rocket engine combustion chambers have been conducted [23,24], as well as analytical/numerical investigations [25][26][27][28] for the prediction of liquid film length, corresponding to the axial length of liquid film until it completes evaporation at dryout point as an important thermal parameter to determine the film cooling rate and to design the injectors for the film coolant. Recently, Fujii et al [3] succeeded in high-speed imaging for the unsteady wavy film dynamics inside a practical 10N-class bipropellant thruster under a combustion condition, quantifying the film velocity of 1m/s and thickness of 10 m. A recent review article by Shine and Nidhi [1] emphasizes that current prediction models for the liquid film length lack the effect of entrainment in particular and still contain many empirical correlations, resulting in the limited applicability. Moreover, the wavy film structure is three-dimensional (3D) in nature, while 3D analyses for the evaporating thin liquid film can be rarely found.…”