1 

A coherent line source in a turbulent atmosphere
The sound field of a coherent line source in a nonrefracting, turbulent atmosphere is studied. An expression for the sound pressure level in the frequency domain is developed, based on a discretization of the line source into a set of point sources. Atmospheric turbulence is taken into account by the mutual coherence function. Numerical computations for various turbulent atmospheres show that the geometrical attenuation is 3 dB per distance doubling (3 dB/dd) at a small distance (cylindrical spreading), 6 dB/dd at a large distance (spherical spreading), and 7.5 dB/dd in a transition region. The anomalous value of 7.5 dB/dd is confirmed by an analytic approximation. Next, a computational method in the time domain is developed, for arbitrary wave forms emitted by the source. Atmospheric turbulence is taken into account in this method by including random fluctuations of the acoustic travel times, based on the spectral density of the travel time correlation function. For a harmonic coherent line source, the method yields results that agree with results computed in the frequency domain.

[Abstract]

2 

Theory of turbulent shear stress
Using dynamical response functions for 3D turbulent shear flow, I calculate the Reynolds stress spectrum on the basis of the inertial range energy spectrum

[Abstract]

3 

Air supply method and indoor environment
A ventilation jet diffuser is characterized by parameters such as diffuser effective area, diffuser dimension, diffuser position, air supply direction, flow rate, and air temperature. This paper studies the influence of the parameters of a jet diffuser on the airflow pattern, indoor air quality, and draft risk in an office with a jet diffuser on the rear wall near the ceiling. The presentation of furniture and occupants in the office is included in the numerical simulation. The structure of a jet diffuser used in practice is complicated. Therefore, a simplified method is introduced to simulate the diffuser. The method is compared with the experimental data. The agreement between the simulations and the measurements is reasonably good. The distributions of the air velocity, temperature, contaminant concentration, and percentage dissatisfied people due to draft risk with different parameters of the diffuser are numerically predicted by the ks model of turbulence. The effect of turbulence intensity is taken into account in the computation of draft risk. It has been found that the angle between the jet and the ceiling should be in the range from 20 to 60°C. The effective flow area has a strong impact on the indoor airflow pattern since it significantly affects the throw projection. The diffuser width has a larger influence on indoor air diffusion than the diffuser height. The distance between the inlet and ceiling has a remarkable influence on the total air movement near the ceiling, but has a minor impact on the air diffusion in the occupied zone. Air velocity distribution is sensitive to ventilation rate and supply air temperature. To achieve the same length of throw projection, the Reynolds number should be the same if the corresponding Archimedes number is close to each of them.

[Abstract]

4 

A model for flowinduced noise of Helmholtz resonatorlike cavities
This paper presents a single prediction model for the noise generated by a turbulent boundry layer flow grazing on the opening of a Helmholtzresonator like cavity. The prediction model is validated by comparison with an experimental study. The measured spectra inside the cavity are correctly predicted by the model.

[Abstract]

5 

The calculation of turbulent reacting flows with a combustion model based on finite chemical kinetics


6 

DNS of turbulent flow and heat transfer in a channel with surface mounted cubes
The turbulent flow and heat transfer in a channel with surface mounted cubical obstacles forms a generic example of a problem that occurs in many engineering applications, for instance in the design of cooling devices. We have performed a numerical simulation of it without using any turbulence models. This approach is the most accurate  but also the most expensive  way of computing complex turbulent flows since all dynamically significant scales of motion are to be solved numerically from the unsteady, incompressible NavierStokes equations and the energy equation. In view of the computational complexity, our first concern is to reduce the computational cost as far as we can get. We discretise convective and diffusive operators such that their spectral properties are preserved, i.e. convection ↔ skewsymmetric; diffusion ↔ symmetric, positive definite. Such a symmetrypreserving discretisation is stable on any grid and conserves mass, momentum and kinetic energy if the dissipation is turned off. First, the results of a secondorder and a fourthorder, symmetrypreserving discretisation are compared for a fully developed, turbulent flow in a plane channel. The more accurate fourthorder method is applied to perform a numerical simulation of turbulent flow and heat transfer in a channel, where a matrix of cubes is mounted at one wall. Here, the temperature is treated as a passive scalar. The Reynolds number (based on the channel width and the mean bulk velocity) is equal to Re = 13, 000. The results of the numerical simulation agree well with the available experimental data.

[Abstract]

7 

Improved jet noise modeling using a new acoustic time scale
To calculate the noise emanating from a turbulent flow (such as a jet flow) using Lighthill's analogy, knowledge concerning the unsteady characteristics of the turbulence is required. Specifically, the form of the turbulent correlation tensor together with various time and lengthscales and convection velocities are needed. However, if we are using a RANS calculation then we obtain only steady characteristics of the flow and it is then necessary to model the unsteady behaviour in some way. While there has been considerable attention given to the correct way to model the form of the correlation tensor (or equivalently the spectral density), less attention has been given to underlying physics that dictate the proper choice of timescale. In early studies various authors tended to assume that the acoustic timescale was proportional to the turbulent dissipation rate but later studies have revealed that a frequency dependent relationship gives better results. In this paper we recognise that there are several time dependent processes occurring within a turbulent flow and propose a new way of defining an acoustic timescale. An isothermal singleflow M0.75 jet has been chosen for the present study and essential fluid dynamic information and turbulent parameters have been obtained using a modified kε method. The jet noise prediction at 90 deg is found using Lighthill's analogy and directivity is estimated using an asymptotic solution of Lilley's formulation. Predictions reveal good agreement between the noise predictions and observations. Furthermore, the new timescale has an inherent frequency dependency that arises naturally from the underlying physics thus avoiding supplementary mathematical enhancements to the model.

[Abstract]

8 

Prediction of the flowinduced noise for practical applications using the SNGR method
In this paper an engineering method for the prediction of noise generated by a turbulent flow is presented. The presented approach is based on the assumption that the acoustic phenomena do not provide feedback to the turbulence. Thus, parameters such as the turbulent kinetic energy and the integral length scale can be obtained from Reynolds Averaged Navier Stokes (RANS) simulations. Subsequently an SNGR approach is employed for generating an unsteady turbulent velocity distribution that possesses these turbulent characteristic values. Since the propagation of sound is little influenced by turbulent and viscous effects it can be described by the Euler equations. These Euler equations are solved on an unstructured grid, allowing for arbitrarily complex geometries. Results of simulations employing this Computational Aero Acoustics approach for several applications are compared with measurements, showing good agreement.

[Abstract]

9 

A review of the wind loading zones for flat roofs in code provisions
The provisions for wind loads on flat roofs differ considerably between current wind loading standards in different jurisdictions. For a number of major wind loading codes, both the definition of roof zones, and the values applied to determine the wind loads are discussed. This paper concentrates on the wind loading zones near edges and corners, with special emphasis on local loads on lowrise buildings. Differences in sizes for edge and roof zones of a factor 2 occur when comparing some of the major wind loading standards. Based on recent wind tunnel results, recommendations are given for further development of these codes

[Abstract]

10 

Measurement of the dry deposition flux of NH3 on to coniferous forest
The dry deposition flux of NH3 to coniferous forest was determined by the micrometeorological gradient method using a 36m high tower. Aerodynamic characteristics of the site were studied, using a second tower erected in the forest 100m from the first. Fluxes and gradients of heat and momentum measured on both towers indicated a fairly homogeneous turbulent flow field over the studied area of the forest. Site specific flux profile functions for heat were derived from continuous measurements of turbulent fluxes and gradients. These functions were used to derive fluxes from the observed gradients of NH3. In total, eighty 90min NH3 flux runs were performed. The results indicate a strong nonstomatal uptake of NH3 by the forest. A representative dry deposition velocity for NH3 of 3.6cm1s was derived. The annual average flux was roughly estimated to be equivalent to 50kg Nha1yr, significantly higher than the critical load for coniferous forest.

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[Abstract]

11 

Influence of turbulent grazing flow on the impedance of an opening
In this paper, the impedance of a rectangular opening submitted to a turbulent grazing flow is investigated experimentally. The opening is located in a flat plate where a turbulent boundary layer flow develops. The impedance is measured with a twomicrophone measuring pipe installed below the opening. The opening has a rectangular shape of large aspect ratio. With the long side oriented perpendicular to the flow. The results, the contribution due to the flow of the acoustic resistance and length correction, are nondimensionalized and compared with equivalent values computed with a vortexsheet model.

[Abstract]

12 

Prediction of wallpressure fluctuations using the statistical approach to turbulence induced noise (Satin)
The noise prediction model SATIN (Statistical Approach to Turbulence /nduced Noise) is presented. SATIN assumes axial symmetric turbulence with the length scale ratio λ and the Reynolds stress ratio ξ as two anisotropy parameters. The model is based on Lighthill's acoustic analogy and allows to predict both the farfield noise radiation as well as nearfield wallpressure fluctuations. In this paper, we focus on the latter because they are usually much larger in amplitude than farfield noise and therefore less sensitive to wind tunnel background noise. Experimental investigations of wallpressure fluctuations under a turbulent boundary layer flow were done by TNOTPD. During the experiments, the flow velocity, the boundary layer thickness and the friction coefficient were varied producing different types of turbulent boundary layers. The wallpressure fluctuations were measured with an array of microphones flush mounted in the wall. Predictions and measurements are compared on the basis of single microphone spectra. Input parameters of SATIN are characteristic values of the turbulent boundary layer, i. e. the boundary layer thickness and the friction coefficient or the friction velocity, respectively. These properties were extracted from measurements of the mean velocity distribution. The measured and predicted wallpressure fluctuations show good agreement. © 2001 by J. S. D. Ostertag, J. Golliard and S. Wagner.

[Abstract]

13 

Investigations to improve and assess the accuracy of computational fluid dynamic based explosion models
article 
1996

Author: 
Popat, N.R.
·
Catlin, C.A.
·
Arntzen, B.J.
·
Lindstedt, R.P.
·
Hjertager, B.H.
·
Solberg, T.
·
Saeter, O.
·
Berg, A.C. van den

Keywords: 
Explosives · Computational fluid dynamics · Explosion models · Calculations · Computer simulation · Explosions · Hazards · Mathematical models · Project management · Risk assessment · Societies and institutions · Explosion models · Hazard assessment · Large scale experiments · Medium scale experiments · Small scale experiments · Air · Computer model · Dangerous goods · Experimental model · Explosion · Flow · Mathematical model · Turbulent flow · Explosions · Gas · Methane, 74828 · Propane, 74986

A summary is given of part of the CEC cosponsored project MERGE (Modelling and Experimental Research into Gas Explosions). The objective of this part of the project was to provide improved Computational Fluid Dynamic explosion models with the potential for use in hazard assessments. Five organisations with substantial experience in both theoretical and experimental explosion modelling contributed to this model assessment study; British Gas, Christian Michelsen Institute, Imperial College, Telemark Technological Research and Development Centre and TNO Prins Maurits Laboratory. The theoretical and numerical basis of the models are described. Results are given of a comparison exercise of model predictions against calculations which were chosen to test the accuracy of the various physical submodels embodied within the overall explosion model. The development phase of the study is also described in which further extensions to the models were made to provide the best achievable agreement with small and mediumscale experiments also conducted as part of the project. The models were finally used to simulate largescale explosion experiments prior to the experiments being conducted. The overall capabilities of the models are reviewed and areas of uncertainty in the physics highlighted. A summary is given of part of the CEC cosponsored project MERGE (Modelling and Experimental Research into Gas Explosions). The objective of this part of the project was to provide improved Computational Fluid Dynamic explosion models with the potential for use in hazard assessments. Five organisations with substantial experience in both theoretical and experimental explosion modelling contributed to this model assessment study; British Gas, Christian Michelsen Institute, Imperial College, Telemark Technological Research and Development Centre and TNO Prins Maurits Laboratory. The theoretical and numerical basis of the models are described. Results are given of a comparison exercise of model predictions against calculations which were chosen to test the accuracy of the various physical submodels embodied within the overall explosion model. The development phase of the study is also described in which further extensions to the models were made to provide the best achievable agreement with smalland mediumscale experiments also conducted as part of the project. The models were finally used to simulate largescale explosion experiments prior to the experiments being conducted. The overall capabilities of the models are reviewed and areas of uncertainty in the physics highlighted.

[Abstract]

14 

Numerical modeling of turbulent jet diffusion flames in the atmospheric surface layer
The evolution of turbulent jet diffusion flames of natural gas in air is predicted using a finitevolume procedure for solving the flow equations. The model is three dimensional, elliptic and based on the conservedscalar approach and the laminar flamelet concept. A laminar flamelet prescription for temperature, which is in agreement with measurements in methane/air flames and accounts for radiative heat losses, has been modified and adapted to naturalgas flames. The kεg turbulence model has been used. Different probabilitydensity functions for the conserved scalar and an alternative method which does not require the use of a pdf are employed. The model has been applied to flames in the buoyancymomentum transition regime, in both cases where the fuel jet is immersed in a coflowing or in a crossflow air stream whose properties correspond to the atmospheric surface layer. Experiments have been carried out for a horizontal flame in a wind tunnel with simulated atmospheric boundary layer, and measurements of temperature distributions are compared with the numerical results; a good agreement is found. The influence of wind properties on flame shape has been investigated. For horizontal flames, a correlation is proposed for the stoichiometric flame length as a function of the Froude number and the wind to jet velocity ratio. Flame length predictions have been compared with available experimental data and correlations proposed in the literature.

[Abstract]

15 

Extension and application of a scaling technique for duplication of inflight aerodynamic heat flux in ground test facilities
To enable direct experimental duplication of the inflight heat flux distribution on supersonic and hypersonic vehicles, an aerodynamic heating scaling technique has been developed. The scaling technique is based on the analytical equations for convective heat transfer for laminar and turbulent boundary layers that follow from applying the Reynolds analogy. The method was developed starting from an elementary isothermal cold flat plate at zero angle of attack and subsequent introduction of wall temperature effects, geometrical scaling effects and angle of attack effects. The present paper extends the scaling technique by introducing correction factors enabling full duplication of the laminar and turbulent boundary layer heat transfer downstream of a shock wave generated by a flat plate at angle of attack. A similar extension is developed to enable full duplication of the laminar and turbulent boundary layer heat transfer downstream of a Prandt Meyer expansion. The scaling technique is applied to a simplified vehicle configuration consisting of two convex surfaces. The results clearly show that scaled test conditions can be derived at which the inflight distribution of heat flux on either one of the two surfaces can be fully duplicated. After implementation of high temperature effects this scaling technique may allow for experimental verification of the heat flux distribution on hypersonic vehicles at supersonic test conditions. In this way, test facilities that are far less expensive to operate can provide valuable information during the initial design phase of a hypersonic vehicle.

[Abstract]
