Effect of lip-thickness on the acoustic characteristics of Hartmann resonator
07 Jun 2010-
TL;DR: In this paper, the effect of lip-thickness on the various acoustic characteristics of a Hartmann resonator placed axisymmetrically in the flow field of a supersonic jet is studied.
Abstract: This paper studies the effect of lip-thickness on the various acoustic characteristics of a Hartmann resonator placed axisymmetrically in the flow field of a supersonic jet. Hartmann resonator is a device wherein supersonic jet impinges at the open end of a cylindrical cavity, which is closed at the other end. Such cavities have numerous applications such as flow control, atomization, ignition initiation etc. The various acoustic parameters such frequency, over all sound pressure level, acoustic slice power etc is determined for a cavity with constant lip-thickness and are compared without lip-thickness. The parameters being considered are the nozzle pressure ratio, stand-off distance (S) between nozzle exit and the cavity inlet, cavity length (L). The jet diameter and the cavity inlet diameter are kept constant (7 mm) for both the cavities. Acoustic pressure is measured in the far field region at emission angles varying from 37 to 135, measured from the jet flow direction. It is observed from spectra that the fundamental frequencies of cavities without and with lip are observed to decrease with increase in cavity length. The effect of lip is observed to have negligible effect on the resonance frequency. The maximum OASPL at a nozzle pressure ratio (NPR) of 4 is observed at an emission angle of 60 – 90 for a cavity without lip where as it is almost at 37 for a cavity with lip. The increase of OASPL to a higher value is more pronounced at a higher nozzle pressure ratio thus illustrating that the effect of lip-thickness. The slice power directivity also shifts to a higher value without lip.
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TL;DR: In this article, an in-depth investigation of the Hartmann tube (HT) was carried out to gain a better understanding of and the effects of various parameters on its output flow characteristics.
Abstract: An in-depth investigation of the Hartmann tube (HT) was carried out to gain a better understanding of and the effects of various parameters on its output flow characteristics. The HT used in this work consisted of an underexpanded jet directed into a close-ended cylindrical tube of the same diameter. The effects of tube depth, separation distance between the tube and the nozzle, and the jet Mach number were explored. Experiments were also performed on an HT fluidic actuator (HTFA). The HTFA operates under the same principles as the HT, except a major portion of the area between the nozzle and tube is shielded off, so that it can be used as a pulsating injector for flow control. Dynamic pressure measurements in the near field and microphone measurements in the far field provided temporal and spectral data. Instantaneous and phase-averaged images of the flow were obtained to explore the nature of turbulence structures within the flow. Limited hot-wire measurements were performed to characterize the velocity fluctuations at the exit of the HTFA
92 citations
TL;DR: A detailed and systematic investigation of the unsteady complex shock structure in this part of the flow region has led to a better understanding of the fundamental mechanisms associated with the gas heating in a resonance tube.
Abstract: Experiments have been performed to determine the basic mechanism of heating in resonance tubes of square section with constant area excited by underexpanded jet flows. The jet flow between the nozzle exit and the tube inlet plays a key role in the performance of a resonance tube. A detailed and systematic investigation of the unsteady complex shock structure in this part of the flow region has led to a better understanding of the fundamental mechanisms associated with the gas heating in such tubes. A study of the effects of tube location in relation to free-jet shock location (without the presence of the resonance tube) has shed further light on the underlying mechanism of sustained oscillations of the flow in a resonance tube.
78 citations
"Effect of lip-thickness on the acou..." refers background in this paper
...[4] studied experimentally the effect of end wall pressure, side wall pressure, end wall temperature and wave velocity along with flow visualization within the resonance tube for wide range of cavity lengths and nozzle pressure ratio....
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TL;DR: In this paper, a high bandwidth powered resonance tube (PRT) actuator potentially useful for noise and flow control applications was developed, and detailed experiments aimed at understanding the PRT phenomenon are complemented by an improved analytical model and direct numerical simulations.
Abstract: A high bandwidth powered resonance tube (PRT) actuator potentially useful for noise and flow control applications was developed. High bandwidth allows use of the same actuator at various locations on an aircraft and over a range of flight speeds. The actuator selected for bandwidth enhancement was the PRT actuator, which is an adaptation of the Hartmann whistle. The device is capable of producing high-frequency and high-amplitude pressure and velocity perturbations for active flow control applications. Our detailed experiments aimed at understanding the PRT phenomenon are complemented by an improved analytical model and direct numerical simulations. We provide a detailed characterization of the unsteady pressures in the nearfield of the actuator using phase averaged pressure measurements. The measurements revealed that propagating fluctuations at 9 kHz were biased towards the upstream direction (relative to the supply jet). A complementary computational study validated by our experiments was useful in simulating the details in the region between the supply jet and the resonance tube where it was difficult to gather experimental data. High bandwidth was obtained by varying the depth of the resonance tube that determines the frequency produced by the device. Our actuator could produce frequencies ranging from 1600 to 15,000 Hz at amplitudes as high as 160 dB near the source. The frequency variation with depth is predicted well by the quarter wavelength formula for deep tubes but the formula becomes increasingly inaccurate as the tube depth is decreased. An improved analytical model was developed, in which the compliance and mass of the fluid in the integration slot is incorporated into the prediction of resonance frequencies of the system. Finally a feedback controller that varied both the resonance tube depth and spacing to converge on a desired frequency was developed and demonstrated. We are optimistic that numerous potential applications exist for such high bandwidth high dynamic range actuators.
52 citations
"Effect of lip-thickness on the acou..." refers background in this paper
...[1] provided the detailed characterization of the unsteady pressures in the near field....
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TL;DR: In this article, the effect of different parameters on the frequency and amplitude of acoustic fluctuations excited when the H-S underexpanded jet impinges on an in-line cavity was studied.
Abstract: Experiments were conducted with a Hartmann–Sprenger tube (H–S) to study the effect of different parameters on the frequency and amplitude of acoustic fluctuations excited when the H–S underexpanded jet impinges on an in-line cavity. Time averaged shadowgraphs were acquired to study the flow field between the underexpanded jet and the cavity for varying parameters of the H–S tube. It was observed that the H–S tube primarily excited two different modes. The first mode corresponds to the jet regurgitant mode (JRG) where the frequency of oscillations scales as a function of the cavity depth. The other mode is screech where an oscillating shock is formed in front of the cavity. The screech mode excites a higher acoustic frequency than the JRG and it is observed to be a strong function of the pressure ratio R, and distance between the jet and the cavity X. At a fixed cavity length, varying standoff distance X could excite either the JRG or screech. At very low standoff distances (X/Dj 1 was found to sustain JRG over a wide range of X. Diameter ratios Dc/Dj<1 sustained high frequency screech modes in a wide range of H–S tube parameters.
40 citations
"Effect of lip-thickness on the acou..." refers background in this paper
...[5] found that there is a mode switch from screech to jet regurgitant at very low spacing (S < 5....
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TL;DR: In this paper, the authors examined the resonance characteristics of the powered resonance tube (PRT) actuator as a function of the operating parameters such as jet-to-tube spacing, tube depth, and nozzle pressure ratio.
Abstract: The powered resonance tube (PRT) actuator and its variants are new developments in active flow control (AFC) technology The PRT is attractive because it has no moving parts and can produce acoustic tones that have amplitudes greater than 150 dB over a large frequency bandwidth The first part of this paper deals with the resonance characteristics of the PRT as a function of the operating parameters such as jet-to-tube spacing (Sp), tube depth (d), and nozzle pressure ratio (NPR) It was found that: (1) at low NPR (333), the PRT resonates at discrete combinations of spacing and depth (2) Using theoretical estimates for predicting shock cell lengths, one could observe a correlation between the theoretical prediction for shock cell length and the spacing at which the PRT resonates (3) At high NPR (429), for a fixed depth, the PRT resonates at virtually all spacings (4) The frequency at which the PRT resonates remains approximately constant, regardless of spacing The second part of the study focused on examining the directivity of the acoustic radiation from the PRT—significant for developing orientation strategies of the PRT with respect to the target flow in the end application The directivity of the fundamental PRT tone and that of its harmonics were studied for a variety of resonance frequencies, both separately as well as cumulatively It was found that the fundamental part of the actuation signal radiated predominantly in the downstream direction of the jet for low resonance frequencies As the resonance frequency was increased from 3 to 12 kHz, the directivity changed from downstream of the jet to vertically upward, and finally upstream of the jet at the higher frequencies
24 citations
"Effect of lip-thickness on the acou..." refers background in this paper
...[6] studied the resonance characteristics of the Hartmann whistle for various parameters (S, L, and NPR) and found that at a low value of NPR = 3....
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