Turbulence models for the computation of flow past airplanes

An increase in the accuracy of identification of Activities of Daily Living (ADL) is very important for different goals of Enhanced Living Environments and for Ambient Assisted Living (AAL) tasks. This increase may be achieved through identification of the surrounding environment. Although this is usually used to identify the location, ADL recognition can be improved with the identification of the sound in that particular environment. This paper reviews audio fingerprinting techniques that can be used with the acoustic data acquired from mobile devices. A comprehensive literature search was conducted in order to identify relevant English language works aimed at the identification of the environment of ADLs using data acquired with mobile devices, published between 2002 and 2017. In total, 40 studies were analyzed and selected from 115 citations. The results highlight several audio fingerprinting techniques, including Modified discrete cosine transform (MDCT), Mel-frequency cepstrum coefficients (MFCC), Principal Component Analysis (PCA), Fast Fourier Transform (FFT), Gaussian mixture models (GMM), likelihood estimation, logarithmic moduled complex lapped transform (LMCLT), support vector machine (SVM), constant Q transform (CQT), symmetric pairwise boosting (SPB), Philips robust hash (PRH), linear discriminant analysis (LDA) and discrete cosine transform (DCT).

https://rua.ua.es/dspace/bitstream/10045/72592/1/2018_Pires_etal_Sensors.pdf

Recognition of Activities of Daily Living Based on Environmental Analyses Using Audio Fingerprinting Techniques: A Systematic Review.

In many practical applications of conical diffusers, the flow is fed by an annular flow passage formed by a center body. Flow separation, which occurs if the center body ends abruptly, is undesirable because it degrades the diffuser performance. The present experiment utilizes magnetic resonance velocimetry to acquire three-component mean velocity measurements for a set of conical diffusers with an annular inlet. The results show strong coupling between the diffuser wall boundary layer development and the wake of the center body. Coanda blowing is used to mitigate the center body wake separation. The diffuser wall boundary layer is thick in the absence of the central separation bubble and separates when Coanda blowing is too strong.

Separation control in a conical diffuser with an annular inlet: center body wake separation

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Separation control in a conical diffuser with an annular inlet

Transport aircraft performance is strongly influenced by the effectiveness of the high-lift system. Wakes subjected to strong adverse pressure gradients in high-lift systems can thicken very rapidly, limiting maximum lift. A combined experimental and computational investigation has been conducted to evaluate performance of several turbulence models in simulating this type of flow. In the experiment, a turbulent wake was subjected to adverse pressure gradients in a symmetric diffuser. LDV surveys, pressure measurements, and flow visualization were used to investigate the physics of this decelerated wake, through the onset of wake reversal. NavierStokes calculations were also performed for a flat plate wake in a two-dimensional diffuser. For diffuser angles similar to the experiment, the calculations under-predicted wake growth and failed to demonstrate wake reversal.

Measurement and simulation of wake deceleration

The present experimental investigation deals with the behaviour of a wake generated by a square cylinder developing in a curved diffuser, a curved duct, a straight duct and a straight diffuser having a same pressure gradient as in the curved diffuser. This enables a systematic study of the effects of curvature and pressure gradient on wake development. It is seen that the curvature makes the wake asymmetric; the wake half width increases on the inner side and decreases on the outer side; the inner side being the region between the centreline and the wall closer to the centre of curvature and the outer side being the region between the centreline and the other wall. It causes a higher entrainment in the inner side as compared to the outer side. An adverse pressure gradient, on the other hand, causes a higher wake growth and velocity defect but reduces the rate of decay of the velocity defect. These are not altered significantly when the curvature and pressure gradient effects are combined. The curvature enhances the Reynolds stresses and the kinetic energy on the inner side and suppresses them on the outer side which makes their profiles asymmetric. These profiles become more and more asymmetric with increase in the streamwise distance. When the effects of curvature and adverse pressure gradient are combined, the profiles become further asymmetric.

Development of a bluff body wake under the combined influence of curvature and pressure gradient

A time-stretching invariant, robust audio fingerprinting method, based on landmarks in the audio spectrogram is proposed in this paper. Time-stretching of audio clips or songs are done to evade copyright detection as most of the fingerprinting techniques are time dependent. Time-stretching is also used in music industry to produce remix & song mash-ups and in multimedia broadcasting to fit content within the required duration. The proposed algorithm is based on the audio hashing of frequency peaks in the spectrogram. It is scalable and tolerant to time-stretching. The experiment results show the method is highly tolerable to time-stretch than the state-of-the-art Shazam's audio fingerprinting.

Scalable and robust audio fingerprinting method tolerable to time-stretching

Experimental data on the development of wakes in a straight duct, a curved duct, a curved diffuser and a straight diffuser are compared with computations based on a finite volume scheme incorporating the k– e model of turbulence. The results show that the computations based on the standard k–e model are able to satisfactorily capture only the mean velocity profiles. To improve the predictions, several modifications to the model are tried out. Close agreement between experiment and computation as regards the velocity profiles, wake parameters and profiles of the turbulent kinetic energy k and Reynolds shear stress ⌅{uv} is obtained when modification to the model constant Cμ, based on the curvature parameter and the ratio of the production of turbulent kinetic energy to its rate of dissipation, is incorporated. The modified model is also able to capture the asymmetry in the profiles of k and ⌅{uv} caused by the curvature and its enhancement due to the additional presence of an adverse pressure gradient.

Prediction of aerofoil wake subjected to the effects of curvature and pressure gradient

The present experimental investigation deals with the behaviour of a wake generated by a square cylinder developing in a curved diffuser, a curved duct, a straight duct and a straight diffuser having a same pressure gradient as in the curved diffuser. This enables a systematic study of the effects of curvature and pressure gradient on wake development. It is seen that the curvature makes the wake asymmetric; the wake half width increases on the inner side and decreases on the outer side; the inner side being the region between the centreline and the wall closer to the centre of curvature and the outer side being the region between the centreline and the other wall. It causes a higher entrainment in the inner side as compared to the outer side. An adverse pressure gradient, on the other hand, causes a higher wake growth and velocity defect but re- duces the rate of decay of the velocity defect. These are not altered significantly when the curvature and pressure gra- dient effects are combined. The curvature enhances the Reynolds stresses and the kinetic energy on the inner side and suppresses them on the outer side which makes their profiles asymmetric. These profiles become more and more asymmetric with increase in the streamwise distance. When the effects of curvature and adverse pressure gradient are combined, the profiles become further asymmetric. 1 Introflaction Thin shear flows with significant streamline curvature and pressure gradient are found in many situations of practical interest; for example, on compressor and turbine blades, multi-element airfoils, and on the valve in the aorta of the human heart. For the multi-element airfoil, the wake behaviour is of particular significance since the wake of the leading edge slat develops in a curved flow. An understanding of the turbulent structure in such flows is of basic importance and would help in improving the prediction techniques.

http://link.springer.com/content/pdf/10.1007%2FBF00211386.pdf

Jacob George

Papers

Development of a bluff body wake under the combined influence of curvature and pressure gradient

Scalable and robust audio fingerprinting method tolerable to time-stretching

Prediction of aerofoil wake subjected to the effects of curvature and pressure gradient

Development of a bluff body wake curvature and pressure gradient