Valdis Kibens

Active flow control using integrated powered resonance tube actuators

This paper reports on a high frequency actuator technology development program for Active Flow Control (AFC). The innovation of using Powered Resonance Tube Bank (PRTB) actuators for the suppression of jet impingement tones is described. The actuator itself consists of a modified Hartmann resonator that is comprised of a jet aimed at the open end of a tube closed at the other end. When suitably designed and integrated, the technique produces high amplitude excitation over a range of frequencies. The resonance tube idea was then developed further into a Boeing/IIT powered resonance tube actuator bank. The actuator bank consists of an array of seven resonance tubes. Two generations of PRTBs were developed. The first (Gen.-I) was successfully applied for cavity noise suppression at DERA, UK (Stanek et al. 2000, 2001). The second (Gen.-II) actuator and its application to jet impingement noise suppression is described in this paper. The Gen.-II actuator is capable of various mass flow injection rates without changing the air pressure supplied to the actuator. Tests conducted at Boeing Saint Louis indicate that Associate Professor, Associate Fellow AIAA + Associate Technical Fellow, Associate Fellow AIAA Copyright

High-Frequency Excitation Active Flow Control for High-Speed Weapon Release (HIFEX)

Traditional weapon release from bays uses a spoiler for modifying the bay shear layer to reduce acoustic levels within the bay and to enhance the characteristics of weapon separation. However, for high-speed weapon release (free stream Mach numbers between 2 and 4), passive devices such as spoilers do not provide a robust means of achieving safe weapon dispense. To address this problem The Boeing Company, under funding from the DARPA Micro Adaptive Flow Control Program, has developed an active flow control approach for high-speed weapon dispense from a bay. Boeing is currently working on preparation for the full-scale demonstration of the concept at the Holloman AFB High-Speed Test Track. This paper reviews the various elements of the HIFEX program performed over the past two years using wind tunnel testing at Mach 2.5 and concludes with plans for the full-scale flow control evaluation in 2005.

Development of Powered Resonance-Tube Actuators for Aircraft Flow Control Applications

The present paper addresses both active-flow-control actuator technology development and the demonstration of the effectiveness of actuators that could be easily integrated into practical aircraft applications. The actuator used is an adaptation of the Hartmann oscillator. Demonstration experiments that illustrate the effectiveness of this actuator include cavity tone suppression at transonic speeds and the reduction of jet-impingement tones. The actuator concept is based on a high-speed jet aimed at the mouth of a cylindrical tube closed at the other end. The result is a high-amplitude self-sustaining fluctuating field accompanied by an intense narrowband tone, all in the region between the supply jet and the resonance tube. Using unsteady pressure sensors and flow visualization, we explored the effect of varying actuator parameters such as the spacing between the power jet and the resonance tube, supply pressure, resonance-tube depth, diameter, shape, and lateral spacing. By varying the depth of the tube, the frequency could be varied from about 1.6 kHz to over 10 kHz and amplitudes as high as 156 dB (microphone location dependent) were obtained in the vicinity of actuation. To integrate this concept into practical aircraft applications, two generations of a more complex version of this device known as the powered resonance-tube bank (PRTB) were developed and demonstrated. Results indicate that by using high-frequency excitation at 5-kHz suppression levels in excess of 20 dB were consistently obtained over a range of operating conditions in both cavity and impingement flow situations. Based on our results, we have grounds to believe that a properly designed PRTB has significant advantages over conventional actuators such as acoustic, piezo, and oscillatory microstructures.

Characterization of High-Frequency Excitation of a Wake by Simulation

Insights into the effects of high-frequency forcing on free shear layer evolution are gained through analysis of several direct numerical simulations. High-frequency forcing of a fully turbulent plane wake results in only a weak transient effect. On the other hand, significant changes in the developed turbulent state may result when high-frequency forcing is applied to a transitional wake. The impacts of varying the characteristics of the high-frequency forcing are examined, particularly, the streamwise wavenumber band in which forcing is applied and the initial amplitude of the forcing. The high-frequency excitation is found to increase the dissipation rate of turbulent kinetic energy, to reduce the turbulent kinetic energy production rate, and to reduce the turbulent kinetic energy suppression increases with forcing amplitude once a threshold level has been reached. For a given initial forcing energy, the largest reduction in turbulent kinetic energy density was achieved by forcing wavenumbers that are about two to three times the neutral wavenumber determined from linear stability theory.

Linear arrays of powered resonance tube actuators for aeroacoustic control

Experiments were conducted to characterize the performance of a linear array of powered resonance tube actuators developed jointly by Boeing and IIT. The actuator is an adaptation of the Hartmann whistle and devices of this type have been shown to be effective in suppressing flow generated acoustic tones that commonly occur in aircraft applications, such as impingement tones and cavity resonances (Raman et al., AIAA Paper 2000‐1930; Stanek et al., AIAA Paper 2000‐1905). The goal of this characterization is to provide a database that can be used to compare the performance of these actuators with other actuator designs (such as piezoelectric actuators) and to optimize the design of these actuators. Optimization involves modifying the geometric parameters of the actuator in order to get the maximum acoustic control with minimum input mass flow rate. In order to accomplish these tasks, detailed measurements of the fluctuating velocity and pressure were made at numerous locations in the flowfield at the actuat...