M.P. Newby

Bio: M.P. Newby is an academic researcher. The author has contributed to research in topics: Jet (fluid). The author has an hindex of 1, co-authored 1 publications receiving 212 citations.

Measurements of entrainment by axisymmetrical turbulent jets

Abstract: A new technique is described for measuring the axial mass flow rate in the turbulent jet formed when a gas in injected into a reservoir of stagnant air at uniform pressure. The jet is surrounded by a porous-walled cylindrical chamber, and air is injected through the wall until the pressure in the chamber is uniform and atmospheric, a condition which is taken to signify that the ‘entrainment appetite’ of the jet is satisfied.Measurements made with the apparatus have allowed the deduction of an entrainment law relating mass flow rate, jet momentum, axial distance and air density, regardless of the injected gas, and including the effects of buoyancy. When the injected gas burns in the jet the entrainment rate is up to 30% lower than when it does not.

The Structure of Diffusion Flames

Abstract: The theory for the mixing and chemical reaction of two streams of fluid is developed for unsteady laminar and for turbulent flow. Only one conserved scalar is required to fully describe the mixing and various reaction models are considered including the Burke-Schumann flame sheet and shifting equilibrium. A new expression is derived for the instantaneous reaction rate of any species Wi = –pD(▿ξ)2Yi/dξ2 where ξ is a conserved scalar. New insight is obtained into the structure of the instantaneous reaction zone for both laminar and turbulent flames. Diagnostic parameters are presented for determining when various models are applicable and for what properties.

Influence of jet exit conditions on the passive scalar field of an axisymmetric free jet

Abstract: The influence of initial flow conditions on the passive scalar field of a turbulent free jet issuing from the round nozzle is investigated in this paper by a review of the literature and a detailed experimental study. Two sets of distinctly different initial conditions are generated using two nozzle types: a smooth contraction and a long straight pipe. The present measurements of the passive scalar (temperature) field were conducted in a slightly heated air jet from each nozzle at a Reynolds number of 16 000 using identical experimental facilities and a single measurement technique. Significant differences between the flows from the two nozzles are revealed throughout the measured flow region which covers the axial range from 0 to 70 jet exit diameters. The study suggests that the differences observed in the statistics of the scalar field may be related to differences in the underlying turbulence structure of the jet in the near field. The present findings support the analytical result of George (1989) that the entire flow is influenced by the initial conditions, resulting in a variety of self-similar states in the far field.

Similarity of the concentration field of gas-phase turbulent jets

Abstract: This work is an experimental investigation of the turbulent concentration field formed when the nozzle gas from a round, momentum-driven, free turbulent jet mixes with gas entrained from a quiescent reservoir. The measurements, which were made with a non-intrusive laser-Rayleigh scattering diagnostic at Reynolds numbers of 5000, 16000, and 40000, cover the axial range from 20 to 90 jet exit diameters and resolve the full range of temporal and spatial concentration scales. Reynolds-number-independent and Reynolds-number-dependent similarities are investigated. The mean and r.m.s. values of the concentration are found to be consistent with jet similarity laws. Concentration fluctuation power spectra are found to be self-similar along rays emanating from the virtual origin of the jet. The probability density function for the concentration is also found to be self-similar along rays. Near the centreline of the jet, the scaled probability density function of jet fluid concentration is found to be nearly independent of the Reynolds number.