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... the difference between the data is less than predicted by the theory. This is supported by figure 10. This figure shows two slot heights, and hence two slot areas, at the same slot velocity. ...
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... a factor of one octave to allow for the shift in the noise frequencies proportional to a characteristic length. This number is somewhat smaller than the observed difference in the SPL's of the two spectra in figure 10. All of these arguments assume that we can apply the lessons learned from round jets to very high aspect-ratio jets. ...
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... plenums were made to allow the incoming flow to settle and distribute along the entire span before exiting the slot. Figure 11 shows the flow path through the wing. The flow first comes into the inlet plenum and then proceeds through rectangular sharp edged slots to the slot plenum. ...
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... will be verified by the HARN data to make sure that it is not associated with a high aspect ratio jet. Figure 12 (a --0 to 80 kHz, b --0 to 20 kHz) shows the noise spectra for several slot jet velocities at a constant freestream velocity and constant slot height of 0.003 in. There are several things to note. ...
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... conventional wings were tested, one with a 30 degree flap spanning the entire span of the wing ( figure 15), and one with a flap deflected 40 degrees spanning the entire wing except for a cut-out region in center span (figure 16 and photo installed in figure 4). This gap simulates a gap in a flap system on a conventional wing that may be present to prevent engine exhaust impingement when extended or for some structural reason, as seen on the Lockheed L-1011 in figure 17. ...
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... the conventional wing with the 30 degree flap was tested. Figures 18a and 18b show a comparison between the conventional wing with the 30 degree flap and the CCW configuration with lowest noise for the equivalent lift case. In the range between 1 kHz and 10 kHz the CCW has noise levels similar to those of the conventional system for the CCW h ~ 0.012 in. ...
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... a conventional wing with a flap spanning the entire span of the wing is not really seen in practice. Most aircraft have a gap in flaps across the span (again see figure 17). This is often due to structural Appendix B B -26 constraints or to prevent engine exhaust from impinging on an extended flap in the case of wing mounted engines. ...
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... tests were performed on the new configuration similar to the previous tests. Figure 19 shows the spectra for the two conventional wings at similar freestream conditions. Notice that the two configurations have two differences, the flap deflection angle and the gap in the flap. ...
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... the traverse translates linearly, it cannot remain on the same polar arc for each angle, thus it was necessary for comparison purposes to scale the data using the r squared law for farfield noise propagation. Figure 21 shows the data acquired for the conventional wings. There appears to be only small changes in the signal with angle. ...
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... The octave-band normalised similarity spectra shown inFigure 4have been derived from the original narrowband linear frequency resolution formulae included in the Supporting Materials, in a similar manner to that described in ref(40), and have been normalised to yield a total sound level of 0 dB for the frequency range shown. ...
Railway tunnel ventilation systems present particular problems for predictions of sound emissions, including the relatively high volumetric flow rates, and a lack of well-established models and empirical data. An investigation was undertaken to support the acoustical design of tunnel ventilation systems on the UK High Speed Two (HS2) project, in view of the project environmental commitments and noise constraints. This was aimed at developing practical prediction models for the flow-induced sound generated by two types of termination device: (i) mesh grilles, and (ii) air curtains. Existing literature was reviewed to identify potential prediction models or approaches. The information obtained from the review was used to develop practical models, validated using available empirical data, including over a relatively wide range of flow velocities.
It is hoped that the learning legacy of this work includes an understanding of some key aspects of the acoustics involved in flow-generated sound from ducted ventilation system termination devices for railway and industrial applications, together with relatively simple and practical approaches to predicting their sound emissions.
... The initial intention for the development of the CC system was for short landing and take-off capability, especially by the US Navy, looking for ways to improve aircraft operation from carriers [97]. Many tests including a full-scale flight test and design works have been carried out on the A-6 Intruder [98]. ...
... Experimental and computational work seeking for a design using trailing-edge blowing to eliminate the trailing-edge flaps, or use leading-edge blowing to eliminate the need for leading-edge slats have been carried out on a Boeing 737 aircraft [97,100]. A joint project [32,101,102] has been carried out by University of Manchester, Cranfield University and BAE Systems to demonstrate new technologies for flapless control, and a drone has been designed named MAGMA which finished its first flight trial in 2017. ...
... The initial intention for the development of the CC system was for short landing and take-off capability, especially by the US Navy, looking for ways to improve aircraft operation from carriers [97]. Many tests including a full-scale flight test and design works have been carried out on the A-6 Intruder [98]. ...
... Experimental and computational work seeking for a design using trailing-edge blowing to eliminate the trailing-edge flaps, or use leading-edge blowing to eliminate the need for leading-edge slats have been carried out on a Boeing 737 aircraft [97,100]. A joint project [32,101,102] has been carried out by University of Manchester, Cranfield University and BAE Systems to demonstrate new technologies for flapless control, and a drone has been designed named MAGMA which finished its first flight trial in 2017. ...
Featured Application
Gust load control, aircraft weight reduction, aircraft drag reduction.
Abstract
Effective control of aerodynamic loads, such as maneuvering load and gust load, allows for reduced structural weight and therefore greater aerodynamic efficiency. After a basic introduction in the types of gusts and the current gust load control strategies for aircraft, we outline the conventional gust load alleviation techniques using trailing-edge flaps and spoilers. As these devices also function as high-lift devices or inflight speed brakes, they are often too heavy for high-frequency activations such as control surfaces. Non-conventional active control devices via fluidic actuators have attracted some attention recently from researchers to explore more effective gust load alleviation techniques against traditional flaps for future aircraft design. Research progress of flow control using fluidic actuators, including surface jet blowing and circulation control (CC) for gust load alleviation, is reviewed in detail here. Their load control capabilities in terms of lift force modulations are outlined and compared. Also reviewed are the flow control performances of these fluidic actuators under gust conditions. Experiments and numerical efforts indicated that both CC and surface jet blowing demonstrate fast response characteristics, capable for timely adaptive gust load controls.
... 8 It was shown that this method gives good results considering round jets. 13 Furthermore, Ahuja et al. 14 showed, that the Tam and Auriault model is also applicable to high aspect ratio jets that are to be considered in the case of circulation control airfoils. Hence it is assumed that the time-domain formulation of the Tam and Auriault model is also valid for the present case. ...
With the advances in reduction of propulsion related noise from aircraft, airframe noise gets more and more into focus. During approach and landing, the high-lift system of the wings becomes one major acoustic source region contributing to the overall emitted noise. One promising approach to reduce this airframe noise is to change the complete high-lift system from a classic three element slat-wing-flap configuration to a slot-less system with active blowing and droop nose. Preceding experimental investigations have shown, that such a configuration may provide a noise reduction above 2 kHz on the model scale. In the present paper both numerical and experimental investigations concerning the acoustics of a high-lift wing with droop nose and active blowing are presented. Thereby, an insight into the acoustic source mechanisms for different aerodynamic setups is provided that in the future will serve as a basis for the design of a low-noise high-lift configuration. It was found, that in principle three source mechanisms are to be considered. In the low to mid frequency domain, mostly turbulence-geometry interaction noise such as trailing edge noise, jet-nozzle interaction noise and curvature noise from the flow being bent around the flap are supposed to be the driving mechanisms. Moreover, the high frequency domain is found to be dominated by mixing noise from the high speed jet.
... The exponent of the jet height and width were derived through a linear regression and were allowed to take any value without constraints. Figure 13 shows the effect of applying the current jet noise scaling laws to the overall sound pressure level (OASPL) extracted from figure 11 in appendix C of reference [17]. Figure 13(a) shows the OASPL normalised using Munro and Ahuja's scaling laws whereas fig. ...
... Comparison of the jet noise scaling laws applied to the data from reference[17] for three different nozzle widths of 6.5, 14.75 and 30 inches (165.1, 374.65 and 762 mm). ...
Noise measurements have been performed on rectangular jets of aspect ratios ranging from 49 to 987 with the aim of determining the appropriate velocity and length scaling to be used in an empirical noise prediction model. The results have shown that the velocity exponent is a function of the nozzle aspect ratio, decreasing with increasing nozzle aspect ratio. In an effort to establish a general prediction model, the velocity exponent of 7 was chosen as the best compromise to represent all the measured data. The analysis of the noise measurements from high aspect ratio nozzles of varying jet height and width has shown that, for the range of aspect ratios considered, the jet sound power level scales with the nozzle height to the power of 3 and the nozzle width to the power of 1. The derived jet noise scaling has been validated with independent experimental data and shows good agreement.
... For high Mach numbers a clear rise in amplitude can be seen at θ ≈ 40 • -this matches with the idea of superdirectivity studied previously by Cavalieri et al. 28 and the results presented by Munro and Ahuja. 8 A smaller peak at θ ≈ 80 • can also be seen at lower velocities. Wavepackets are believed to be a promising model for understanding jet noise. ...
We present results for the near-field velocities and far-field acoustics of a rectangular jet. The results show a clear split in behaviour between roughly incompressible Mach numbers and higher Mach numbers. For the incompressible region we find that the peak frequency of fluctuations in the near-field matches that in the far-field acoustics and that the relevant lengthscale for this behaviour is the momentum thickness of the exit boundary layer. The peak frequency being governed by StΘ = 8.5 × 10−3. Flow fluctuations in this region are visualised using high-speed Schlieren imaging. For higher Mach numbers the far-field acoustics is best described by a constant Helmholtz number behaviour peaking at kh = 0.1.
From the far-field acoustics we can determine that there are no spanwise modes present in the jet and that there is strong evidence for the presence of wavepackets. The results also show a change in the directivity pattern with increasing Mach number; the low speed region exhibiting a slight figure-of-eight pattern becoming almost omnidirectional at higher Mach numbers.
Poröse Materialien wurden in Messungen bereits erfolgreich zur Reduktion des an der Hinterkante eines turbulent umströmten Flügelprofils entstehenden Schalles eingesetzt. Ihre akustische Wirkung beruht auf einer gewissen Durchlässigkeit für turbulente Wirbel. Die numerische Betrachtung erlaubt eine detaillierte Analyse der Schallerzeugung an der porösen Hinterkante und damit die Suche nach aeroakustisch maßgeschneiderten Materialien.
This thesis was conducted as a contributing report to an ongoing NASA Research Announcement (NRA,#NNL07AA55C). The NRA investigates potential advanced commercial transport designs that could be utilized in the N+2 time frame (about 2025). The basis of the advanced design revolves around a heavily researched technology called Circulation Control that will be investigated through computational and wind tunnel methods for its feasibility in commercial aviation. The work of this thesis evaluates two potential meshing topologies when conducting CFD; Unstructured and Structured Meshing. Greatest challenges faced was handling the complexity of the computational model and capturing the correct physics that consisted of highly complex, 3-D, ow interactions. The complicated physics include mixing of subsonic/transonic uid, engine jet entrainment, and extreme lift from the circulation control jet ow. Results from this thesis showed that the Unstructured Meshing method applied introduced non-physical ow phenomenon not exhibited when applying Structured Meshing. The latter approach showed to be the superior method in its ability to capture the complicated physics of a circulation control aircraft. As promising the results were, it still remains inconclusive at this time. Further investigation is still required to completely evaluate the accuracy of the two meshing methodologies employed. At the time of this thesis, wind tunnel data was not available, thus remains a variable when evaluating the two different meshing topologies. In addition, this thesis was constrained by limited computational resources and software tools. Thus, the tribulations faced with Unstructured Meshing could have potentially resulted from these two external factors. Further investigation into alternative software tools that allow more user control should be considered next, in addition to having access to more computational resources. Although Unstructured Meshing showed to be inferior in this thesis, these remaining factors need to be eliminated before concluding Unstructured Meshing as not feasible for studying circulation control applications. Numerous studies[1, 2, 3] for 2-D circulation control applications have shown that Unstructured Meshing can be accurate, but the verdict is still out for 3-D models. This thesis yielded encouraging results and helps to aid further research in addressing this critical component for accurate numerical simulation.
Abstract—Circulation Control, which was discovered accidentally
by Henry Coanda in 1935, is proven to be an efficient lift
augmentation method at low Mach numbers. The objective
of this research is to design and develop a Circulation Control
Wing (CCW) that will provide increased lift to a fixedwing
Unmanned Aerial Vehicle (UAV). The configuration (the
curvature of the trailing edge on a Clark-Y airfoil) that gives
high lift augmentation ratios for reasonably low blowing rates
is investigated. Wind tunnel tests are conducted on 11:7% thick
circulation control airfoil with upper surface blowing capability.
Different trailing edges (Coanda surfaces) have been tested at
moment coefficients from 0:0 to 0.04. Test data are collected
at Mach numbers of 0.021; 0.024; 0.029 and 0.030 at Reynolds
numbers of 1x 10^5 to 1.5x10^5. It is found that the smaller
Coanda surface configuration is more effective. At M = 0:021
and � = 13^o, the (2:1) Coanda surface gave the maximum
�CL = 0.42 at a C� = 0.04. The maximum lift enhancement
(up to 155%) at zero angle-of-attack, is achieved by using the
same Coanda surface(2:1) at C�μ = 0.04 and M = 0.03.
