Simulation of the evolution of aircraft exhaust plumes including detailed chemistry and segregation

The Field Monte Carlo or Stochastic Fields (SF) method for turbulent reacting flows has been applied to the chemical evolution of the early part of a hot jet with bypass flow producing 7kN of thrust, using a 23 species chemical mechanism. This is done to broadly approximate a turbofan engine at idle thrust setting. Much of the chemistry was found to take place inside the core of the jet before mixing occurs, as there is no reactant gradient there, considering segregation makes little difference. Radical concentrations, however, were found to be changed. The reaction between NO and ambient O 3, which is slow compared to the fast mixing timescale of the turbulent jet, is unaffected by segregation. The local Damköhler number was calculated based on an estimate of the chemical timescale and the local large-eddy timescale. It was found that only those species which had local Da greater than five were affected by segregation. In this work we have applied the SF method the early part of the plume, however the method developed here could equally be employed to study the plume over a longer distance

Simulations of the dispersion of reactive pollutants in a street canyon, considering different chemical mechanisms and micromixing

The Stochastic Fields (SF) or Field Monte Carlo method has been used to model the dispersion of reactive scalars in a street canyon, using a simple chemistry and the CBM-IV mechanism. SF is a Probability Density Function (PDF) method which allows both means and variances of the scalars to be calculated as well as considering the effect of segregation on reaction rates. It was found that the variance of reactive scalars such as NO2 was very high in the mixing region at roof-top level with rms values of the order of the mean values. The effect of segregation on major species such as O3 was found to be very small using either mechanism, however, some radical species in CBM-IV showed a significant difference. These were found to be the seven species with the fastest chemical timescales. The calculated photostationary state defect was also found to be in error when segregation is neglected

Effect of flame-induced geometrical straining on turbulence levels in explosions and common burner configurations

International Journal of Engineering Science308983-1002IJES

Assessment of the use of cold gas in a windtunnel to investigate the influence of thermal effects on the dispersion of LNG vapour clouds

SIGLEAvailable from British Library Document Supply Centre- DSC:9106.17(CUED/A-AERO/TR--14) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Experiments on some effects of obstacles on dense-gas dispersion

6.00Available from British Library Document Supply Centre- DSC:9091.9(SRD/R--407) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Effect of geometrical straining on turbulence levels in explosions and common burner configurations

SIGLEAvailable from British Library Document Supply Centre- DSC:9106.17(CUED/A-THERMO/TR--29) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

LES and RANS for turbulent flow over arrays of wall-mounted obstacles

Large-eddy simulation (LES) has been applied to calculate the turbulent flow over staggered wall-mounted cubes and staggered random arrays of obstacles with area density 25%, at Reynolds numbers between 5 × 10^3 and 5 10^6, based on the free stream velocity and the obstacle height. Re = 5 × 10^3 data were intensively validated against direct numerical simulation (DNS) results at the same Re and experimental data obtained in a boundary layer developing over an identical roughness and at a rather higher Re. The results collectively confirm that Reynolds number dependency is very weak, principally because the surface drag is predominantly form drag and the turbulence production process is at scales comparable to the roughness element sizes. LES is thus able to simulate turbulent flow over the urban-like obstacles at high Re with grids that would be far too coarse for adequate computation of corresponding smooth-wall flows. Comparison between LES and steady Reynolds-averaged Navier-Stokes (RANS) results are included, emphasising that the latter are inadequate, especially within the canopy region