The paper reports on measurements in the flow generated by a jet issuing from a circular outlet in a wall into a cross-stream along this wall. For the jet-to-crossflow velocity ratios R of 0.5, 1 and 2, the mean and fluctuating velocity components were measured with a three-sensor hot-wire probe. The hot-wire signals were evaluated to yield the three mean-velocity components, the turbulent kinetic energy, the three turbulent shear stresses and, in the case of R = 0.5, the terms in the turbulent-kinetic-energy equation. The results give a quantitative picture of the complex three-dimensional mean flow and turbulence field, and the various phenomena as well as their dependence on the velocity ratio R are discussed in detail.

Experimental investigation of jets in a crossflow

Infrared thermography transforms the thermal energy, emitted by objects in the infrared band of the electromagnetic spectrum, into a visible image. This feature represents a great potentiality to be exploited in many fields, but this technique is still not adequately enclosed in industrial instrumentation because of a lack of adequate knowledge; at first sight, it seems too expensive and difficult to use. The aim of the present paper is to shortly overview existing work and to describe the most relevant experiences devoted to the use of infrared thermography in three main fields, i.e. thermo-fluid dynamics, technology and cultural heritage, which have been performed in the department the authors belong to. Results may be regarded from two points of view, either as validating infrared thermography as a full measurement instrument, or as presenting infrared thermography as a novel technique able to deal with several requirements, which are difficult to perform with other techniques. This study is also an attempt to give indications for a synergic use of the different thermographic methods and sharing experiences in the different fields.

http://iopscience.iop.org/article/10.1088/0957-0233/15/9/R01/pdf

Recent advances in the use of infrared thermography

Spectral analysis and flow visualization are presented for various velocity ratios and Reynolds numbers of a jet issuing perpendicularly from a developing pipe flow into a crossflow. The results are complete with conditional averages of various turbulent quantities for one jet-to-cross-flow velocity ratio R of 0.5. A unique conditional-sampling technique separated the contributions from the turbulent jet flow, the irrotational jet flow, the turbulent crossflow and the irrotational crossflow by using two conditioning functions simultaneously. The intermittency factor profiles indicate that irrotational cross-flow intrudes into the pipe but does not contribute to the average turbulent quantities, while the jet-pipe irrotational flow contributes significantly to them in the region above the exit where the interaction between the boundary-layer eddies and those of the pipe starts to take place. Further downstream, the contributions of the oncoming boundary-layer eddies to the statistical averages reduce significantly. The downstream development depends mainly on the average relative eddy sizes of the interacting turbulent fields.

On the structure of jets in a crossflow

We present numerical solutions of the fully three-dimensional flow of a round, turbulent jet emitted normal to a uniform free stream. Comparisons with available laboratory data and comparison between different numerical grid resolutions are used to demonstrate the quality of the simulation. Examination of the detailed flow pattern within a computational domain, which extends 15 jet diameters from the source allows us to follow the vorticity dynamics in the transition from an initially vertical jet to a wake with a vortex pair essentially aligned with the free stream. The transition is presented as a function of the ratio of the jet exit velocity to free stream velocity. For large velocity ratios, the source of the streamwise vorticity in the vortex pair can be readily traced back to the original streamwise vorticity in the sides of the vertical jet.

On the vorticity dynamics of a turbulent jet in a crossflow

Film cooling characteristics of a single round hole at various streamwise angles in a crossflow: Part I effectiveness

Measurements are presented of mean temperature in a nonbuoyant heated jet issuing perpendicularly into a cold stream at velocity ratios R=0.25, 0.5, 1, and 2, and of velocity‐temperature fluctuation statistics at R=0.5. The mean temperature profiles at the jet exit are found to be considerably nonuniform at low velocity ratios, indicating an early mixing between the cold and hot fluid. The extra rate of strain due to streamline curvature and the longitudinal and normal temperature gradients affect the rate of generation of temperature fluctuations and turbulent heat fluxes. There are regions of the flow where the streamlines are unstably curved but the generation of ∼(ϑ2) is damped. The eddy diffusivity is well behaved across the flow only at downstream positions where the turbulent Prandtl number has rather high values close to the wall and reaches values around 0.9 away from the wall.

J. Andreopoulos

Papers

Heat transfer measurements in a heated jet‐pipe flow issuing into a cold cross stream