Experimental study of the flows in a non-axisymmetric ellipsoid under precession

Precession driven flows are of great interest for both, industrial and geophysical applications. While cylindrical, spherical and spheroidal geometries have been investigated in great detail, the numerically and theoretically more challenging case of a non-axisymmetric cavity has received less attention. We report experimental results on the flows in a precessing triaxial ellipsoid, with a focus on the base flow of uniform vorticity, which we show to be in good agreement with existing theoretical models. As predicted, the uniform vorticity component exhibits two branches of solutions leading to a hysteresis cycle as a function of the Poincaré number. The first branch is observed at low forcing and characterized by large amplitude of the total fluid rotation and a moderate tilt angle of the fluid rotation axis. In contrast, the second branch displays only a moderate fluid rotation and a large tilt angle of the fluid rotation axis, which tends to align with the precession axis. In addition, we observe the occurrence of parametric instabilities early in the first branch, which saturate in the second branch, where we observe the same order of the kinetic energy in the base flow and instabilities.

Nonlinear oscillations of the interface of two liquids at the angular oscillations of the tank

The development of rocket and space technology in recent years has led to the widespread use of various cryogenic liquids. To increase the shelf life of cryo-products on board spacecraft or in tankers of future space filling stations, it is proposed to create a certain stock of cryo-product, which is simultaneously in a two-phase or three-phase state and forms layers of liquid. The paper considers the problem in a nonlinear formulation about the oscillations of the interface of a two-layer liquid in an arbitrary axisymmetric cavity of a solid body performing angular oscillations around a horizontal axis. For the considered class of cavities with an arbitrary bottom and a lid, the nonlinear problem is reduced to the sequential solution of linear boundary value problems. Nonlinear differential equations describing the oscillations of the interface between two liquids in the vicinity of the main resonance are obtained. In the case of a circular cylindrical cavity with flat bottoms, solutions of boundary value problems in the form of cylindrical functions were used to calculate linear and nonlinear hydrodynamic coefficients depending on the depth and density of the upper liquid.

Anisotropic Borehole Response from Pressuremeter Testing in Deep Clay Shale Formations

This paper presents the result of five pressuremeter tests conducted in deep three clay shale formations at a thermal operation site. Pressuremeter loading was imposed parallel to the bedding plane under an approximately undrained condition and test data were analyzed using the axisymmetric cavity expansion theory. In parallel with triaxial test results, the analyses revealed several constitutive characteristics of the Westgate clay shale, in particular, the limited nonlinearity and the stress/strain-path dependency of shear modulus. A procedure is proposed to correct the data including multi-azimuth radial displacement measurements in the caliper plane and the anisotropic response of the borehole can be studied. Two aspects of azimuthal anisotropy are assessed - 1) in-plane anisotropy of borehole stiffness and 2) the anisotropy in expansion after borehole plastic yielding. The latter provides the implication of anisotropic in-situ horizontal stresses, demonstrated by both experimental and numerical evidence. The influence of the radial and azimuthal variations of the elastic stiffness around borehole on the interpreted orientation of in-situ horizontal stresses is discussed. An agreement is shown between the interpreted azimuth of major/minor in-situ horizontal stress and the reported crustal stress orientation for the test least affected by such the stiffness variation.

Flow characteristics of Axisymmetric Cavity Rear Wall Divergence Angle in a Scramjet Combustor

Non-reacting experimental study was performed on a rear wall angled cavity actuated supersonic flow of Mach 1.5 from a convergent divergent nozzle using a blowdown wind tunnel test setup. Ten different model combinations of double angled rear wall cavities is preferred for the study of improvements in the geometrical design of the combustor. Flow field properties of various cavity geometries were analyzed based on the key parameters like, wall static pressures, stagnation pressure loss to the flow and qualitative mixing of flow using momentum flux distribution. The static pressure is found to decrease inside the combustor with a decrease in the secondary dual rear wall angle below 90 degrees whereas value increases at the rear wall OWING to oscillation and recompression of shear layers inside the cavity region. In addition, the decrement in primary rear wall angle, an enhancement in mixing profile and a reduction in stagnation pressure loss are also observed.

Measurement of the Excitation Source of an Axisymmetric Shallow Cavity Shear Layer

The interaction of a cavity shear layer with the sound field of an acoustic mode can generate an aeroacoustic source which is capable of initiating and sustaining acoustic resonances in the duct housing the cavity. This aeroacoustic source is determined experimentally for an internal axisymmetric cavity exposed to high Reynolds number, fully developed turbulent pipe flow without the need to resolve the details of neither the unsteady flow field nor the flow-sound interaction process at the cavity. The experimental technique, referred to here as the standing wave method (SWM), employs six microphones distributed upstream and downstream of the cavity to evaluate the fluctuating pressure difference generated by the oscillating cavity shear layer in the presence of an externally imposed sound wave. The results of the aeroacoustic source are in good agreement with the concepts of free shear layer instability and the fluid-resonant oscillation behavior. The accuracy of the measurement technique is evaluated by means of sensitivity tests. In addition, the measured source is used to predict the self-excited acoustic resonance of a shallow cavity in a pipeline. Comparison of the predicted and measured results shows excellent prediction of the self-excited acoustic resonance, including the resonance frequency, the lock-in velocity range, and the amplitude of the self-generated acoustic resonance.

Effect of Axisymmetric Aft Wall Angle Cavity in Supersonic Flow Field

Cavity plays a significant role in scramjet combustors to enhance mixing and flame holding of supersonic streams. In this study, the characteristics of axisymmetric cavity with varying aft wall angles in a non-reacting supersonic flow field are experimentally investigated. The experiments are conducted in a blow-down type supersonic flow facility. The facility consists of a supersonic nozzle followed by a circular cross sectional duct. The axisymmetric cavity is incorporated inside the duct. Cavity aft wall is inclined with two consecutive angles. The performance of the aft wall cavities are compared with rectangular cavity. Decreasing aft wall angle reduces the cavity drag due to the stable flow field which is vital for flame holding in supersonic combustor. Uniform mixing and gradual decrease in stagnation pressure loss can be achieved by decreasing the cavity aft wall angle.