Petr Eret

A parametric study of installed counter rotating open rotors

This paper reports on the results of a series of aeroacoustic measurements of a counter rotating open rotor (CROR) installed on a 1/7 scale model of an advanced regional aircraft design. The tests were conducted in a large low speed wind tunnel for a wide range of aircraft configurations. The paper reports the results for the aircraft model in a pusher configuration at take off settings. In total there were 16 aircraft configurations tested consisting of 9 pusher and 7 tractor configurations in both take off and approach settings. The aircraft model consisted of a modular design featuring interchangeable tail pieces, variable fuselage length, engine pylon rotation and elongation and was controllable for angle of attack. Far field measurements were acquired for each configuration using three beamforming microphone arrays and a linear far field microphone array centered on the front blade plane. Near field measurements were made using a traversing arm on 7 planes centered on the front blade plane. This paper will present the results of a parametric study of the CROR noise emission including far field noise maps, CROR source spectra and directivity and the influence of the model geometry on interaction tones. The results reported here are limited to three model configurations designed to investigate the influence of the model tail on far field noise levels. This work has been conducted as part of the European Clean Sky funded WENEMOR project which will be completed in August 2013, the testing phase of which was completed in May 2013.

The application of advanced beamforming techniques for the noise characterization of installed counter rotating open rotors

This paper reports on the results of a series of aeroacoustic measurements of a counter rotating open rotor (CROR) installed on a 1/7 scale model of an advanced regional aircraft design. The tests were conducted in a large low speed wind tunnel for a variety of aircraft geometries, angles of attack and flow speeds. Data were acquired on three far field beamforming arrays. The study attempts to characterize the installed CROR noise source through the application of several beamforming techniques applied to each individual array and to a global array of the three arrays in combination. Although some results have been achieved in this preliminary study, there are also drawbacks and limitations of the beamforming processes for the case of model with CRORs, therefore a deeper investigation will be necessary. This work has been conducted as part of the European Clean Sky funded WENEMOR project which will be completed in August 2013, the testing phase of which was completed in May 2013.

Microphone Arrays as a Leakage Detection Tool in Industrial Compressed Air Systems

Compressed air energy is expensive, but common in industrial manufacturing plant. However, a significant part of the generated compressed air energy is lost due to leakage. Best practice requires ongoing leak detection and repair. Leak detection in the ultrasonic frequency range using handheld devices is possible only over short distances as associated high-frequency sound is rapidly attenuated by atmospheric absorption. Pressurized air escaping to ambience also generates frequencies below 20u2009kHz. In this paper beamforming—a well known method for generating noise maps—is tested as a tool for localization of compressed air leaks at larger distances in the audible frequency range. Advanced beamforming methods in both time domain (broadband) and frequency domain (narrowband) have been implemented in a variety of situations on a laboratory experimental rig with several open blows representing leakage in a noisy environment similar to a factory setting. Based on the results achieved it is concluded that the microphone array approach has the potential to be a robust leak identification tool. The experience gained here can also provide useful guidance to the practitioner.

A practical approach to investigating energy consumption of industrial compressed air systems

While there are several best practice standards available for minimizing the energy requirement for compressed air use in an industrial context, moving to best practice often requires investment and operational change. In production facilities, there is often a reluctance to commit to this type of change without a clear view of the benefit. Furthermore, there is very little detailed information available in the open literature that allows even a qualitative assessment of priorities. In order to address this shortcoming, a practical approach is proposed to provide detailed compressed air consumption information throughout an industrial site. The energy of the compressed air is evaluated at each key element of the system and the typical end-use application profile assessed. Simple models of the consumption rates are used to relate duty cycle and device count with actual total consumption. This approach is complemented with a novel method of assessing the leak rate from the entire system, based on the pressure decay time. The method, referred to as the ‘end use catalogue’ has been demonstrated at a manufacturing site with a wide range of compressed air applications. The model has been used to identify the most significant energy-intensive compressed air applications and possible strategies to reduce the energy requirement. In the particular site used as a demonstration, it was found that open blowing operations (e.g. fluidizing) are the largest consumers of compressed air which are amenable to intervention. System leakage accounts for almost 21u2009peru2009cent of the compressed air generated, representing an energy input of 432 kWh per day. It is concluded that this approach can help to identify priorities for optimizing compressed air use at an industrial site without compromising the production yield.

Experimental observations of an installed-on-pylon contra-rotating open rotor with equal blade number in pusher and tractor configuration:

Noise from contra-rotating open rotors is a major obstacle to the adoption of this fuel efficient technology as a viable aircraft propulsion system. A better understanding of both contra-rotating open rotor noise generation and reduction has been achieved due to ongoing extensive research. One of the most recent research activities is the WENEMOR (wind tunnel tests for the evaluation of the installation effects of Noise EMissions of an open rotor advanced regional aircraft) project, which has been developed in response to the requirements described in the Clean Sky-Integrated Technology Demonstrators under the heading of Green Regional Aircraft. The project investigates the airframe installation effects of a 1 / 7 th scale model of a regional aircraft equipped with two contra-rotating open rotors of the same rotor diameter, the same rotational speed and equal blade number. For this case, the blade passing frequency of rotor-alone tones and the frequency of relevant interaction tones cannot be distinguished due to the equal blade count of the two rotors. This study presents the tone directivity plots up to 4u2009×u2009blade passing frequency of the isolated WENEMOR single pylon contra-rotating open rotor engine in both pusher and tractor configurations at various angles of incidence and flow velocities. A linear array of 13 microphones is deployed for the far field sound measurements. The tone directivity trends show the efficient on-axis acoustic radiation at all blade passing frequency tones with the contra-rotating open rotor tone at 2u2009×u2009blade passing frequency dominating in the vast majority of the tests. The main objective is to compare the acoustic emission of pusher and tractor configurations tested under the same flow velocities and angles of incidence. The results suggest that the pusher configuration of the isolated contra-rotating open rotor tends to be slightly louder than the tractor at 2u2009×u2009blade passing frequency. However, it is shown that the acoustic performance of the isolated contra-rotating open rotor is complicated and sensitive to any change in the flow velocity and the angle of incidence. The increasing flow velocity and the increasing angle of incidence show limited consistency in proportional trends in the directivity plots of sound pressure levels. It is anticipated that the findings will be different for a more realistic case of installed-on-model contra-rotating open rotor.

A coupling of computational methods for CROR installation effects

This paper deals with the computation of CROR installation effects in terms of tone noise within three separated steps. The first step aims at computing the aeroacoustic sources of a CROR by a CFD approach, namely a URANS method applied to counter-rotative propellers. The second step computes the acoustic field radiated by the isolated CROR. It is based on the Ffowcs-Williams and Hawkings (FW-H) surface integral method and uses the blade pressure fluctuations computed by CFD as input data. The last step computes the acoustic field scattered by the aircraft geometry within the Boundary Element Method using the incident acoustic field previously computed. This approach in three steps is applied on a 1/7 scale model of a regional aircraft design equipped with two CRORs and tested in windtunnel. The paper first focuses on the aeroacoustic study of the CROR including the effects of pylon and incidence. The numerical prediction of the CROR noise in take-off conditions is then compared to the experimental measurements of the isolated engine. The isolated CROR noise computation is globally underestimated compared to the measurements because it doesn’t take into account the acoustic reflections occuring in the windtunnel but a qualitative agreement is found between the computation and the measurements. Finally, the computation of CROR installation effects is presented in one of the aircraft configuration tested in windtunnel, showing a global increase of the tones when the CROR is installed in comparison with the isolated configuration.

Compressed Air Leak Detection Using Microphone Array Techniques

Compressed air leakage is a well known issue and means loss of the expensive industrial utility. The energy loss is embedded in a product and thus any compressed air leakage reduction directly affects LCA. The traditional method for leak detection such as ultrasonic hand held leak detector is limited in application to very short distances. In this paper, the concept of a microphone array operating in the audible frequency range is used to localize compressed air leaks. Both advanced time and frequency domain beamforming methods have been demonstrated on a laboratory experimental rig with several open blows representing leakage. The preliminary results have shown the applicability of the concept and suggest that microphone array approach has potential to be a robust leak identification tool.

Industrial Compressed Air Use: Two Case Studies

While there are several best practice standards available for minimizing the energy requirement for compressed air use in an industrial context, moving to best practice often requires investment and operational change. In production facilities, there is often a reluctance to commit to this type of change without a clear view of the benefit. Furthermore, there is very little detailed information available in the open literature that allows even a qualitative assessment of priorities. In order to address this shortcoming, analyses of two industrial compressed air systems which are already installed in manufacturing plants have been conducted in the context of energy usage. The installations are quite different in compressed air needs: one is focused on actuation and drying; while the other uses compressed air primarily for material handling. In both sites, the energy of the compressed air is evaluated at each key element of the system and the typical end use application profile is assessed. Simple models of the consumption rates are used to relate duty cycle and device count with actual total consumption. A new way of assessing the leak rate from the entire system has been developed, based on the pressure decay time, and has been implemented at one site. In this way, the energy balance of the system entire has been analyzed quantitatively, with the effect of distribution leaks accounted for directly. It is found that in both sites, open blowing operations (e.g. drying) are the largest, consumers which are amenable to optimization. It is also found that the measured leak rate at one site represented 23% of the compressed air generated, with an energy input of 455kWh per day. It is concluded that this approach can help to identify priorities for optimizing CA use at an industrial site.Copyright

Estimation of Non-Linear Damping Parameters in a Normal Triangular Array Subject to Fluidelastic Instability

The non-linear damping parameters associated with a coupled fluidelastic system have been extracted using the non-linear decrement method. The response of a single flexible tube in a five row normal triangular tube array (P/d = 1.32) was recorded over a range of freestream velocities with air as the working fluid. The structural damping has been set so as to avoid fluidelastic instability. The linear and cubic fluidelastic damping parameters have been obtained. Using these identified quantities, the limit cycle amplitudes for the system at lower structural damping levels have estimated. Good agreement between the predicted values and the experimental data is achieved.Copyright