Investigation of Stabilization Effects in Hartmann-Sprenger Tubes

Abstract

An experimental investigation has been conducted in order to evaluate whether it is possible to reduce the sensitivity of the heating effect observed in Hartmann-Sprenger Tubes by applying swirl to the nozzle flow. A reference configuration derived from literature is compared against modified cavities incorporating stems of various lengths and a setup utilizing swirl. A stem of ≈50% cavity length has been found to have a moderate effect on operating mode stability and heating effects. Subjecting a cylindrical resonator to swirling flow has demonstrated to considerably increase the amplitude of the flow oscillations, leading to detrimental effects on heating rate due to increased mass transfer from cavity to environment. The swirl configuration therefore shows potential for improving resonators used for active flow control and Hartmann-Sprenger tubes designed for larger pressure amplitudes.

Hartmann–Sprenger Energy Separation Effect for the Quasi-Isothermal Pressure Reduction of Natural Gas: Feasibility Analysis and Numerical Simulation

“…The mass transfer between the cavity of the resonator and the surrounding flow is reduced, which makes it possible to reach the highest temperatures inside the resonator precisely in this operating mode. The highest efficiency is observed for relatively short resonators [69,74].…”

“…At subsonic speeds, an increase in efficiency can be achieved by crossing the exit section of the nozzle with a thin wire (the Mach number is 0.73) [89] or using elements [90] that reduce the stability of the jet near its surface. For all modes of operation of the nozzle-resonator pair, various pins can be used, which are installed either along the axis of the resonator [34,74] or along the axis of the nozzle [41,91]. Installing a pin with a length of about half (56%) of the effective length of the internal cavity of the resonator increases the heating rate by focusing the compression shocks in the resonator by narrowing its effective cross-section area and increasing the amplitude of oscillations inside the resonator [74].…”

“…For all modes of operation of the nozzle-resonator pair, various pins can be used, which are installed either along the axis of the resonator [34,74] or along the axis of the nozzle [41,91]. Installing a pin with a length of about half (56%) of the effective length of the internal cavity of the resonator increases the heating rate by focusing the compression shocks in the resonator by narrowing its effective cross-section area and increasing the amplitude of oscillations inside the resonator [74]. However, it should be kept in mind that such a pin allows the resonator to function in regurgitant mode in a wider pressure range.…”

“…When using the Hartmann-Sprenger effect, the question of the influence of acoustic impact and vibrations on the surrounding systems and structures is important. The noise pressure level at a certain resonant frequency can reach 100 db and higher [67,74,95]. The noise level is reduced when the resonant tube is operated at higher frequencies [88].…”

“…The noise level is reduced when the resonant tube is operated at higher frequencies [88]. In this case, the peaks in the sound spectrum will refer either to the natural oscillation frequency of the resonator (lower frequencies), or to the regurgitant mode, screech mode, or their intermediate mode [74]. Since sound is mechanical oscillations, its presence cannot but be accompanied by vibrations, which can be significant depending on the field of application [40,45].…”