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The interaction of vortex rings with thin wire mesh screens is investigated using laser-induced fluorescence (LIF) and molecular tagging velocimetry (MTV). The existence of vortex shedding from individual wires of the porous screens, suggested by prior works, is shown and compared to flow visualization results. A range of interaction Reynolds numbers and screen porosities are studied to determine the conditions affecting the interaction. Transmitted vortex (TV) ring formation is shown to be a function of vortex shedding and the shedding Reynolds number, but not a function of porosity. Screen porosity is shown to affect the TV convective speed but did not impact the formation behaviors. Three major flow regimes existed for the interaction: TV formation with no vortex shedding, TV formation with visible vortex shedding, and no downstream formation with strong shed vortices.

This paper describes recent advances in the development of a temperature measurement methodology based on phosphorescence of a tracer molecule in a liquid. The methodology represents an extension of molecular tagging velocimetry (MTV). MTV is a laser-based technique of obtaining spatially resolved fluid velocity profiles. The methodology has the potential of providing spatially resolved simultaneous measurements of velocity and temperature data over a planar domain. Presently, a method of obtaining temperatures over a range of 30°C with a typical uncertainty of ±1.0–1.5°C has been developed. Recent progress has resulted in a method of generating robust calibration curves for use in subsequent temperature measurements. A discussion of the experimental methodology, calibration curve development, and error analysis is presented. Finally, simultaneous temperature and velocity profile measurements using the method are demonstrated under dynamic conditions.

Multiple line Molecular Tagging Velocimetry (MTV) measurements are used to explore the flow fields associated with wall region negative ∂u˜/∂y in a low Rθ turbulent boundary layer. Velocity and velocity gradient statistical profiles establish the present flow as a canonical flat plate boundary layer. Spatial correlations of ∂u/∂y in the (x, y) plane, and the probability of observing negative ∂u˜+/∂y+ exceeding a negative threshold of −0.25 reveal the highly significant presence of negative ∂u˜/∂y in the region 25 ≤ y+ ≤ 35. Examination of the instantaneous flow fields underlying the conditional pdf indicates that there are two primary contributing motions: (i) streamwise shear layers and (ii) compact regions containing ±∂u˜/∂y. The importance of these motions to wall region turbulence production is discussed.

This review article provides an overview of the experimental studies of in-cylinder flows using various flow measurement techniques with a focus on molecular tagging velocimetry. It is necessary to understand the evolution of large-scale and small-scale turbulence as prepared during the intake stroke with a cycle resolved quantitative description. Due to the difficulty in obtaining these descriptions, either by modeling or experimentally, they are often characterized with somewhat ambiguous notions of bulk swirl and tumble measurement methods. During the intake stroke, in-cylinder flows are formed in such a manner as to provide advantageous spatial and temporal behavior for mixture formation later during the compression stroke. Understanding the details of how these flows influence fuel-air mixing, the initiation of ignition, combustion, and subsequent flame propagation processes is the primary motivation for the development of the methods described in this paper. The authors provide an introduction to fundamental flow motion inside the engine cylinder and measurement techniques, e.g., hot-wire anemometry, laser Doppler anemometry, and particle image velocimetry. Furthermore, molecular tagging velocimetry is discussed in detail in terms of (i) different mechanisms, (ii) procedure and data reduction methods to obtain the desired flow properties such as velocity, vorticity, and turbulent intensities, and (iii) applications to flow studies in internal combustion engines. Finally, the significance of experimental investigations of in-cylinder flows is discussed along with possible future applications.

An experimental study is performed to investigate the cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow measurement inside an internal combustion engine assembly. Molecular tagging velocimetry (MTV) is used to obtain the multiple point measurement of the instantaneous velocity field. MTV is a molecular counterpart of particle-based techniques, and it eliminates the use of seed particles. A two-component velocity field is obtained at various crank angle degrees for tumble and swirl measurement planes inside an optical engine assembly (1500 rpm and 2500 rpm engine speeds). Effects of charge motion control are studied considering different cases of: (i) charge motion control valve (CMCV) deactivated and (ii) CMCV activated. Both the measurement planes are used in each case to study the cycle-to-cycle variability inside an engine cylinder. Probability density functions of the normalized circulation are calculated from the instantaneous planar velocity to quantify the cycle-to-cycle variations of in-cylinder flows. In addition, the turbulent kinetic energy of flow is calculated and compared with the results of the probability density function. Different geometries of CMCV produce different effects on the in-cylinder flow field. It is found that the charge motion control used in this study has a profound effect on cycle-to-cycle variations during the intake and early compression; however, its influence reduces during the late compression. Therefore, it can be assumed that CMCV enhances the fuel-air mixing more than the flame speed.