The oblique impingement of circular turbulent jets on smooth walls has been studied both experimentally and analytically. This type of flow represents a considerable degree of geometrical generalit...

Oblique impingement of circular turbulent jets

Experimental investigations and theoretical calculations devoted to studying different aspects of the formation of clusters in two-phase flows are reviewed. The physical mechanisms of the formation of the regions of increased concentrations of particles in turbulent flows and under flowing bodies by two-phase streams, as well as in free concentrated vortices, are considered.

Clusterization of particles in turbulent and vortex two-phase flows

Effect of chevron count and penetration on the acoustic characteristics of chevron nozzles

Accurate and efficient computation of the nearest wall distance d (or level set) is important for many areas of computational science/engineering. Differential equation-based distance/level set algorithms, such as the hyperbolic-natured Eikonal equation, have demonstrated valuable computational efficiency. Here, in the context, as an ‘auxiliary’ equation to the main flow equations, the Eikonal equation is solved efficiently with two different finite volume approaches (the cell-vertex and cell-centered). The application of the distance solution is studied for various geometries. Moreover, a procedure using the differential field to obtain the medial axis transform (MAT) for different geometries is presented. The latter provides a skeleton representation of geometric models that has many useful analysis properties. As an alternative to other methods, the current d-MAT procedure bypasses difficulties that are usually encountered by pure geometric methods (e.g. the Voronoi approach), especially in three dimensions, and provides better accuracy than pure thinning methods. It is also shown that the d-MAT approach provides the potential to sculpt/control the MAT form for specialized solution purposes.

Finite volume distance field and its application to medial axis transforms

In spite of recent advances in LES methods, RANS based jet noise prediction models appear to be the only realistic, near term, approach for the development of a jet noise prediction procedure that is applicable to chevron nozzle flows, or other advanced nozzle designs. The present paper describes the application of such a model to a series of chevron nozzle flows and the model predictions are compared with experimental data. It is shown that the chevr ons affect t he flow in two important ways. The f irst effect is that the axial vortices cause a very rapid increase in the width of the mixing layer. This process, in effect, leads to a local im balance between the turb ulence and the mean flow, a reduction i n the turbulence production, and an overall reduction in the peak turbulence level, thus contributing to a noise reduction at the lower frequencies. The second is more complex and appears to involve an interaction between the axial vortices and the jet tur bulence that causes more of the high frequency noise from this region to be radiated to the far field. The strength of this new noise source appears to scale with the strength of the axial vortices.

Noise Predictions for Chevron Nozzle Flows

Several experimental, computational and theoretical results devoted to turbulence jet noise are described. All these results were obtained at CIAM in collaboration with the Boeing Company. The selected topics are combined and described from a single point of view. In spite of the many publications in the classical literature devoted to jet noise, many jet noise problems are not completely solved, and most current jet noise prediction methods are still highly empirical and rely heavily on an existing experimental data base. At the same time, many of the available experimental results are not fully reliable and some are even contradictory. The goal of this paper is, therefore, to explore and discuss some of the possibilities and limitations of classical aeroacoustics methods.

On the prediction of turbulent jet noise using traditional aeroacoustic methods

The results of an investigation of the unsteady flow structure in a turbulent swirling jet obtained using the PIV technology are presented. The greater part of the measurements is carried out at the swirl intensity W
 0 ≈ 1.7. A part of the data is obtained under other conditions of the swirl jet outflow. To establish the relation between disturbances of different types the phase averaging technique is employed with the pressure fluctuation in the acoustic field of the jet taken as a reference signal. The flow structure is numerically calculated. The results of the investigation show that a quasisteady inhomogeneity observable in the jet flow executes rotational motion relative to the mean flowfield in the jet cross-section, or “precession”. It causes disturbances in the flow ejected by the jet, which transform into acoustic disturbances far away from the jet. The frequencies of the dynamic disturbances near the jet and the acoustic disturbances far away from it coincide with the precession frequency.

Investigation of unsteady processes, flow properties, and tonal acoustic radiation of a swirling jet

In the previous experimental studies it was concluded that the turbulent jet noise is produced by large-scale motions in the mixing layer induced by turbulence intermittence. The burden of this numerical simulation is the validation of these conclusions. As a result of numerical calculations, the “instantaneous” flow patterns and the parameter distributions in the initial regions of turbulent jets are obtained. On the basis of this information the flow dynamics are investigated. In the jet flow there are observable slowly transforming low static pressure regions and zones of elevated static pressure. These regions are displaced at the convection velocity. The inflow induced by the low pressure in the mixing layer has streamlines entering into the low pressure zones and flowing around the elevated pressure zones. The motion of the zones of the static pressure varying along the flow produces velocity disturbances in the induced external flow. The succession of the transformations of the intermittence-induced static pressure disturbances into sound waves is determined. This transformation occurs in the regions occupied by the ejected air.

Investigation of noise generation by turbulent jets on the basis of numerical simulation of unsteady flow in mixing layers

A model of noise generation in the mixing layer of a jet is proposed on the basis of the measurements of the acoustic radiation of a free jet by means of a microphone system, which makes it possible to determine the location of sources of sound at a given frequency, and hot-wire measurements of the velocity of the motion of vortices of given dimensions in the mixing layer. It is shown that the acoustic wave generation can be attributed to turbulence intermittence in the jet, that is, an unsteady motion of a region occupied by a “turbulent fluid”. As a result, an unsteady motion of the air ejected by the jet produces acoustic waves.

An attempt to localize the sound sources in a turbulent jet using the results of the measurements of the acoustic field and the velocity fluctuation correlations

The article gives the results of calculations of non-self-similar flows in turbulent jets. Use is made of the approximation of a boundary layer [1-3]; in the case of a high degree of twisting, when a zone of reverse flow forms in the initial section, the consideration is begun in a cross section corresponding to the end of the above zone. With a numerical solution the flow parameters are determined consecutively in cross sections located downstream from the starting cross section, where they are given by the conditions of the problem. The article gives a generalized Prandtl formula for the turbulent viscosity for the cases of the flows under consideration. The results of calculations carried out using this formula are compared with experimental data. The corresponding experimental constants are determined. An integral theory is proposed describing twisted jet flows with a weak deformation of the profiles of the gas-dynamic parameters.

S. Yu. Krasheninnikov

Papers

On the prediction of turbulent jet noise using traditional aeroacoustic methods

Investigation of unsteady processes, flow properties, and tonal acoustic radiation of a swirling jet

Investigation of noise generation by turbulent jets on the basis of numerical simulation of unsteady flow in mixing layers

An attempt to localize the sound sources in a turbulent jet using the results of the measurements of the acoustic field and the velocity fluctuation correlations

Calculation of axisymmetric twisted and nontwisted turbulent jets