No abstract

The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum.

Three-dimensional (3D)—steady-developing-laminar-isothermal—and gravity-driven thin liquid film flow adjacent to an inclined plane is examined and the effects of film flow rate, surface tension, and surface inclination angle on the film thickness and film width are presented. The film flow was numerically simulated using the volume of fluid model and experimental verification was conducted by measuring film thickness and width using a laser focus displacement instrument. The steady film flow that is considered in this study does not have a leading contact line, however, it has two steady side contact lines with the substrate surface at the outer edge of its width. Results reveal that the film width decreases and the average film thickness increases as the film flows down the inclined plane. The film thickness and width decrease but its streamwise velocity increases as surface inclination angle (as measured from the horizontal plane) increases. A higher film flow rate is associated with a higher film thickness, a higher film width, and a higher average film velocity. Films with higher surface tension are associated with a smaller width and a higher average thickness. A ripple develops near the side contact line, i.e., the spanwise distribution of the film thickness exhibits peaks at the outer edges of the film width and the height of this ripple increases as the surface tension or the film flow rate increases. The width of the film decreases at a faster rate along the streamwise direction if liquid film has higher surface tension. Measurements of the film thickness and the film width compare favorably with the numerically simulated results.

Combustion instability in liquid rocket engines can have severe consequences including degraded performance, accelerated component wear, and potentially catastrophic failure. High-frequency instabilities, which are generally the most harmful in liquid rocket engines, can be driven by interactions between disturbances associated with transverse acoustic resonances and the combustion process. The combustion response to acoustic perturbation is a critical component of the instabililty mechanism, and is in general not well understood. The current paper describes an experimental facility at the Air Force Research Laboratory (AFRL) at Edwards Air Force Base that is intended to investigate the coupling between transverse acoustic resonances and single/multiple liquid rocket engine injector flames.Critical aspects of the facility will be described, including the capability to operate at supercritical pressures that are relevant to high-performance liquid rocket engines, accurately-controlled and cryogenically-conditioned propellants, and optical access to facilitate the use of advanced diagnostics. The transverse acoustic resonance is induced through the use of carefully-controlled piezoelectric sirens, allowing monochromatic excitation across a range of amplitudes at a number of discrete frequencies. The location of the flame within the acoustic resonance mode shape can also be varied through relative phase control of the two acoustic sources. The operating space of the facility, for oxygen and hydrogen operation, will be described. Preliminary nonreacting and reacting data will also be presented to demonstrate the quality of operation of this facility. It is anticipated that future results generated using this facility will provide both fundamental insight into the acoustic-flame interactions as well as provide a database useful for validating combustion instability models. NomenclatureA = area c = speed of sound 2 D 1 = inner injector inner diameter D 2 = inner injector outer diameter D 3 = outer injector inner diameter D 4 = outer injector outer diameter dt = time step f F = acoustic frequency m = waveguide flare constant p c = mean chamber pressure pʹ = acoustic pressure perturbation amplitude t = inner post thickness uʹ = acoustic velocity perturbation amplitude x = streamwise (longitudinal) coordinate axis y = spanwise (transverse) coordinate axis z = depthwise coordinate axis

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.