Jet Noise Reduction in Co-Flowing Jets with Finite Lip Thickness

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
S. Kevin Bennett ◽  
R. Naren Shankar
Keyword(s):  
Passive Control ◽  
Recirculation Zone ◽  
Near Field ◽  
Jet Noise ◽  
Free Jet ◽  
Turbulent Eddies ◽  
Primary Core ◽  
Mixing Noise ◽  
Bypass Ratio ◽  
Convective Mach Number

Passive control for suppressing mixing noise from Co-Flowing Jets (CFJ) is presented in this study. The idea behind this is to reduce the convective Mach number of turbulent eddies that produce intense sound radiation. The present study analyses co-flowing jets with a bypass ratio of 6.3 and the primary nozzle lip thickness of 10 mm. The aim of the study is to find the jet noise level in finite lip thickness in co-flowing jets. CFJ with finite lip thickness forms a recirculation zone (in the near field). The secondary core and recirculation zone are shielding the primary core by reducing the jet noise. A single free jet with a diameter equal to that of a primary nozzle of co-flowing jet is also studied for comparison. The results show that co-flow jet with finite lip thickness of 10mm for various emission angles and the Overall Sound Pressure Level (OASPL) level gets reduced when compared with the single free jet.

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

2021 ◽  
Vol 20 (1-2) ◽  
pp. 4-34
Author(s):  
Reda R Mankbadi ◽  
Saman Salehian
Keyword(s):  
Large Scale ◽  
Flat Surface ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Dominant Frequency ◽  
Wavy Surface ◽  
Initial Region ◽  
Reflected Waves ◽  
Free Jet

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

scholarly journals Passive control of structures for seismic loads

2000 ◽  
Vol 33 (3) ◽  
pp. 209-221 ◽  
Author(s):  
Ian G. Buckle
Keyword(s):  
High Performance ◽  
Passive Control ◽  
Base Isolation ◽  
Mechanical Energy ◽  
Near Field ◽  
The United States ◽  
Industrial Plant ◽  
Passive Systems ◽  
Limit States ◽  
Existing Structures

The control of structures to improve their performance during earthquakes was first proposed more than a century ago. But it has only been in the last 25 years that structures have been successfully designed and built using earthquake protective systems. Today these systems range from simple passive devices to fully active systems. This paper focuses on passive control and reviews recent developments in the state-of-the-art. Passive systems include tuned mass dampers, seismic (base) isolation systems, mechanical energy dissipators, and the like. Major developments in the theory, hardware, design, specification, and installation of these systems have permitted significant applications to buildings, bridges, and industrial plant. Applications are now found in almost all of the seismically active countries of the world, but principally in Italy, Japan, New Zealand and the United States. Noteworthy advantages have been demonstrated when retrofitting existing structures, and designing high-performance structures such as hospitals, emergency response facilities, defense installations, and critical bridges. Field experience in recent earthquakes has confirmed these expectations. There are however limitations to the use of passive systems and these deserve further study and research. They include the uncertainty of response in the near field of an active fault, the non- optimal behavior of passive systems for both small and large earthquakes, and a lack of certainty about the ultimate limit states in unexpectedly large events. As a consequence, in some jurisdictions, code provisions for passive systems are more onerous than for conventional construction, which is a strong disincentive to their use. The limited availability of design guidance in text books, code commentaries, and other design aids are further impediments to the wider use of these systems.

Characteristics of a co-flowing jet with varying lip thickness and constant bypass ratio

2019 ◽  
Vol 91 (9) ◽  
pp. 1205-1213 ◽  
Author(s):  
Naren Shankar R. ◽  
Kevin Bennett S.
Keyword(s):  
Design Methodology ◽  
Critical Value ◽  
Commercial Aircraft ◽  
Critical Limit ◽  
Potential Core ◽  
Content Type ◽  
Free Jet ◽  
The Past ◽  
Bypass Ratio ◽  
Practical Implications

Purpose Subsonic commercial aircraft operate with turbo-fan engines that operate with moderate bypass ratio (BR) co-flowing jets (CFJ). This study aims to analyse CFJ with constant BR 6.3 and varying primary nozzle lip thickness (LT) to find a critical LT in CFJ below which mixing enhances and beyond which mixing inhibits. Design/methodology/approach CFJ were characterized with a constant BR of 6.3 and varying lip thicknesses. A single free jet with a diameter equal to that of a primary nozzle of the co-flowing jet was also studied for comparison. Findings The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and magnitude of BR. Practical implications The BR value of CFJ in the present study was 6.3. This lies under the moderate BR value at which subsonic commercial turbofan operates. Hence, it becomes impervious to study its mixing behavior. Originality/value This is the first effort to find the critical value of LT for a constant BR for compressible co-flow jets. The CFJ with moderate BR and varying LT has not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

PREDICTION OF NOISE GENERATED BY A ROUND NOZZLE JET FLOW USING COMPUTATIONAL AEROACOUSTICS

2011 ◽  
Vol 19 (03) ◽  
pp. 291-316 ◽  
Author(s):  
ALI UZUN ◽  
M. YOUSUFF HUSSAINI
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Internal Flow ◽  
Jet Flow ◽  
Computational Aeroacoustics ◽  
Far Field ◽  
Free Jet ◽  
Grid Points ◽  
Field Noise ◽  
Inflow Conditions

This paper demonstrates an application of computational aeroacoustics to the prediction of noise generated by a round nozzle jet flow. In this study, the nozzle internal flow and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large-eddy simulation (LES) code with overset grid capability. To simulate the jet flow field and its radiated noise, we solve the governing equations on approximately 370 million grid points using high-fidelity numerical schemes developed for computational aeroacoustics. Projection of the near-field noise to the far-field is accomplished by coupling the LES data with the Ffowcs Williams–Hawkings method. The main emphasis of these simulations is to compute the jet flow in sufficient detail to accurately capture the physical processes that lead to noise generation. Two separate simulations are performed using turbulent and laminar inflow conditions at the jet nozzle inlet. Simulation results are compared with the corresponding experimental measurements. Results show that nozzle inflow conditions have an influence on the jet flow field and far-field noise.

Influence of bypass ratio on subsonic and correctly expanded sonic co-flowing jets with finite lip thickness

2018 ◽  
Vol 233 (7) ◽  
pp. 2536-2548 ◽  
Author(s):  
S Thanigaiarasu ◽  
R Naren Shankar ◽  
E Rathakrishnan
Keyword(s):  
Total Pressure ◽  
Strong Influence ◽  
Static Pressure ◽  
Pressure Variation ◽  
Jet Mixing ◽  
Free Jet ◽  
Pressure Decay ◽  
Sonic Jet ◽  
Mach Numbers ◽  
Bypass Ratio

The effects of bypass ratio on co-flowing subsonic and correctly expanded sonic jet decay have been studied experimentally. Co-flowing jets with lip thickness 1.0 Dp (where Dp is the diameter of primary nozzle and is equal to 10 mm) with bypass ratios of around 0.7, 1.4, and 6.4 at primary jet exit Mach numbers 0.6, 0.8, and 1.0 have been analyzed. A single free jet equivalent to primary nozzle of the co-flowing nozzle was considered for comparison. Primary jet centerline total pressure decay, spread, and static pressure variation were investigated. The results show that the mixing of the high bypass ratio co-flowing jet with lip thickness 1.0 Dp is superior to low bypass ratio co-flowing jet. Both lip thickness and bypass ratio have a strong influence on the co-flowing jet mixing. Bypass ratio 6.3 experiences a significantly higher mixing than bypass ratio 0.7 and 1.4. Selected jets were also investigated computationally. The computations capture the salient flow physics and reproduce well with the experiments.

Validation of Jet Noise Simulations and Resulting Insights of Acoustic Near Field

AIAA Journal ◽  
2019 ◽  
Vol 57 (12) ◽  
pp. 5156-5167 ◽  
Author(s):  
W. C. P. van der Velden ◽  
D. Casalino ◽  
P. Gopalakrishnan ◽  
A. Jammalamadaka ◽  
Y. Li ◽  
...  
Keyword(s):  
Near Field ◽  
Jet Noise

Characteristics of a co-flowing jet with varying lip thickness and constant velocity ratio

2020 ◽  
Vol 92 (4) ◽  
pp. 633-644
Author(s):  
Naren Shankar R. ◽  
Kevin Bennett S. ◽  
Dilip Raja N. ◽  
Sathish Kumar K.
Keyword(s):  
Constant Velocity ◽  
Velocity Ratio ◽  
Critical Limit ◽  
Potential Core ◽  
Content Type ◽  
Free Jet ◽  
Current Scenario ◽  
Wake Zone ◽  
Bypass Ratio ◽  
Practical Implications

Purpose This study aims to analyze co-flowing jets (CFJs) with constant velocity ratio (VR) and varying primary nozzle lip thickness (LT) to find a critical LT in CFJs below which mixing enhances and beyond which mixing inhibits. Design/methodology/approach CFJs were characterized with a constant VR and varying LTs. A single free jet with a diameter equal to that of a primary nozzle of the CFJ was used for characteristic comparison. Numerical simulation is carried out and is validated with the experimental results. Findings The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and constant VR. A new region termed as influential wake zone is identified. Practical implications In this study, the VR is maintained constant and bypass ratio (BR) was varied from low value to very high values. Presently, subsonic commercial turbo fan operates under low to ultra-high BR. Hence the present study becomes vital to the current scenario. Originality/value To the best of the authors’ knowledge, this is the first effort to find the critical value of LT for a constant VR for compressible co-flow jets. The CFJs with constant VR and varying LT have not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

scholarly journals Exo-Skeletal Engine: Novel Engine Concept

2003 ◽  
Author(s):  
Christos C. Chamis ◽  
Isaiah M. Blankson
Keyword(s):  
Noise Reduction ◽  
Open Channel ◽  
Jet Noise ◽  
Element Model ◽  
Combined Cycle ◽  
Engine Design ◽  
Potential Benefits ◽  
Immense Potential ◽  
Bypass Ratio ◽  
Engine Concept

The Exo-Skeletal Engine concept represents a new radical engine technology with the potential for a substantial revolution in engine design. It is an all composite drum rotor engine in which conventional heavy shafts and discs are eliminated and are replaced by rotating casings that support the blades in spanwise compression. Thus the rotating blades are in compression rather than in tension. The resulting open channel at the engine centerline has immense potential for jet noise reduction, and can also accommodate an inner combined-cycle thruster such as a ramjet. The Exo-Skeletal Engine is described in some detail with respect to geometry, components and potential benefits. Initial evaluation, results for drum rotors, bearings and weights are summarized. Component configuration, assembly plan and potential fabrication processes are also identified. A finite element model of the assembled engine and its major components are described. Preliminary results obtained thus far show at least 30 percent reduction of engine weight and about 10 db noise reduction, compared to a baseline conventional high bypass-ratio engine. Potential benefits in all aspects of engine technology are identified and tabulated. Quantitative assessments of potential benefits are in progress.

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