Search

An experimental investigation of the parameters controlling the whistling frequency and amplitude of an orifice in a confined turbulent flow is undertaken. A circular single hole orifice with sharp edges, a hole diameter equal to 0.015 m and a thickness equal to 0.005 m, is arranged in an air test rig with an inner diameter equal to 0.03 m. The Mach number ranges around 0.02 and the Reynolds number around 10(4). Variable reflecting boundary conditions are arranged upstream and downstream, and several flow velocities are tested. It is found that the Bode-Nyquist criterion accurately predicts the conditions of self-sustained oscillation and the value of the whistling frequency. Furthermore, it is found that the acoustic velocity in whistling regime varies from 1% to 15% of the steady flow velocity, and that it depends on the overall acoustic reflection of the surrounding pipe and on the Strouhal number.

Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number, the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced.Copyright © 2011 by ASME

Whistling phenomena in pipe power plants have been observed in the past years. It occurs at pressure drop devices where vortex shedding is established. It generates high noise levels and excessive vibrations. Auregan and Starobinsky [1] have developed an experimental criterion to predict whistling frequencies of pressure drop devices submitted to plane propagating pressure waves. This criterion estimates the net acoustic power, an acoustic exergy generation indicating that the device behaves as an acoustic amplifier. The corresponding frequencies are potential whistling frequencies. The application of the criterion only requires the determination of the scattering matrix of the device. In previous works, this criterion was applied to different single hole orifices. The purpose of the present study is to apply the criterion to two orifices in series and to verify that the behavior of this system can be predicted from the scattering matrix of each individual orifice and of the straight pipe in-between. Measurements are done on an air test rig with an inner diameter of 3 cm, a Mach number of 2.6 × 10−2 and a Reynolds number of 104 . Different distances between orifices are characterized. The study of the influence of the second orifice on the whistling criterion shows an enhancement of the whistling potential and a shift of the main potential whistling frequency. A fair agreement is found between experimental and predicted results. Characterization of orifices in series is then possible from the coefficients of the scattering matrix of one orifice and an appropriate condition on the distance between the orifices.Copyright © 2009 by ASME

Strong tonal noise can be found on the main steam lines of power plants. The source of noise was identified to be located at the gate valves present on the steam lines. Analysis of on-site measurements showed that the source of noise was due to the cavity that forms the valve seat at the bottom of the valve body. The valve in its open position is then composed of this bottom cavity over which an unstable shear layer develops but also of the top cavity where the gate is stored in open position. The valve is of course also connected to the pipe. All these elements are good candidates for flow-acoustic phenomena. The development of the shear layer over the cavity gives rise to self-sustained flow oscillations and noise radiation. The vortices convected in the shear layer which develops from the upstream corner of the cavity interact with the downstream corner of the cavity. A pressure disturbance is then generated and acts as a feedback loop on the separation point at the upstream corner. Due to the phase relationship between the generation of the disturbance downstream and its influence upstream, this pressure feedback selection amplifies the shear layer and preferred modes of oscillation are then produced. It is also well known that at low Mach number these pressure oscillations in the cavity remain weak. However, in ducted configurations, powerful tones can be generated even at low Mach number when pressure oscillations in the shear layer couple with the acoustical response of the duct. In order to study these phenomena in configurations close to the industrial ones, both numerical and experimental approaches are carried out. A high-order numerical code has been developed in order to capture aeroacoustic interactions in turbulent flows. An experimental test rig has been built in order to study aeroacoustic phenomena in small scale models of control flow devices present on steam pipes of power plants. A vacuum pump is used instead of a ventilator for creating the flow through the test rig in order to study high pressure loss devices. The present paper aims at handling the flow-acoustic phenomena in the case of a fully 3D geometry of the gate valve. Both numerical and experimental investigation methods are used. In the second section of the paper, industrial problem and previous study are recalled. In the third section, the small scale model that is used for both numerical and experimental investigations is presented. In the fourth section, the numerical methods used in this paper are presented. In the fifth section, the experimental device and the measurements techniques are presented. In the sixth section, results of the acoustic modal analysis of the valve are analysed. In the seventh section, results of the flow-acoustic analysis of phenomena in the valve are analysed.