Laser Doppler anemometry measurements in an axisymmetric turbulent jet

Abstract

The present study was performed to investigate experimentally some aspects related to the characteristics of turbulent jet flow using laser Doppler anemometry (LDA) as a measuring technique. It includes the following: (1) investigation of the effect of the velocity bias on the experimental results of the mean and fluctuating velocities, (2) study of the effect of upstream conditions on the mean and turbulent velocity profiles at the jet exit plane, (3) measurement of the decay rate of the center line longitudinal mean velocity and compared results with empirical correlations, (4) examination of the achievement of self-preservation of the jet flow, (5) investigation of whether the flow is approaching isotropy, (6) measurement and documentation of the distribution of the radial mean as well as turbulent velocity profiles. The axial and radial velocity components were measured simultaneously at the same location of the flow using a 5 W argon-ion laser Doppler anemometry. The LDA operated in the fringe Pattern mode, in two-component colors, and in the backscattering detection mode. The present study was carried out for the Reynolds number Ree=104 (based on the nozzle exit diameter D and the center line longitudinal mean velocity at the nozzle exit diameter Ue) up to an axial distance of 45D. In addition, seven cases of initial upstream conditions were investigated. The obtained results revealed that no correction for the velocity bias is needed when the turbulence intensity is low (below 15%). Further, the mean velocity profiles cannot uniquely identify the state of a jet flow. In addition, the effect of the upstream conditions is pronounced mainly in the near field region. Meanwhile the jet flow approaches a certain degree of isotropy in the far field.

The effects of turbulent jet flows on plant cell suspension cultures

“…It is likely that, for many jet properties, strict similarity is fully established only at axial distances in excess of 30-40 diameters. However, recent data presented by Kassab et al (1996) suggest that the longitudinal velocity conforms to the Gaussian profile of Equation (2), even at distances as low as 4 to 20 diameters. The literature contains much information on the values of the constants to be used in the above equations for a wide range of operating conditions.…”

“…This approach is based upon the assumption that the entrained flow will not, on average, penetrate into the central jet region in which energy dissipation is at its highest. The foregoing assumption seems to be well-founded; experimental findings (Kassab et al, 1996) suggest that, in the region 6d to 16d, the radial component of the velocity is small, never exceeding 4% of the nozzle velocity, and is outwardly directed. The implication of this assumption is that the intense mixing and re-entrainment in the receiving vessel, particularly in the early stages of the jetting cycle, does not lead to multiple exposures of a cell to high-intensity disruptive forces.…”

A borescopic laser Doppler velocimetry probe

“…Common examples of turbulent jets include drinking fountains, drain flows into rivers, and chimney discharges into the atmosphere (Kassab et al, 1996).…”

“…Convergent nozzles are used to accelerate subsonic fluids up to sonic velocity. Kassab et al (1996) used laser Doppler anemometry to investigate certain aspects related to the characteristics of turbulent jet flow, including:…”

Borescopic Laser Doppler Velocimetry Probe

“…Blasius 1912: α = 0.143; C = 8.74 Duncan et al 1967: α = 0.111; C = 10.6 Zagarola and Smits 1998: α = 0.137; C = 8.70 McKeon et al 2004: α = 0.142; C = 8.493.3 CONVERGENT NOZZLE JET FLOWNozzles are described as convergent when they narrow from a wide diameter to a smaller diameter. Convergent nozzles are used to accelerate subsonic fluids up to sonic velocity Kassab et al (1996). used laser Doppler anemometry to investigate certain aspects related to the characteristics of turbulent jet flow, including:The effect of velocity bias on the experimental results of the mean and fluctuating velocities.…”