The earliest studies of jet in crossflow were concerning the gross flow behaviour, such as, the jet trajectory, jet penetration, jet spreading, mean velocity fields, and effect of the cross-sectional shapes of the nozzle using the empirical methods (Keffer and
Baines, 1963, Pratte and Baines, 1967, Abramovich, 1963). Little was known then about the non-stationary phenomena and the coherent structures of the jet, which are related to the mixing and entrainment. Some early studies of jets in a crossflow were reported by Ruggeri and Callaghan in a series of publications (Callaghan and Ruggeri 1948, 1951, Ruggeri et al., 1950, Ruggeri, 1952). In these studies the effects of changing the shape of the orifice and of heating the jet on a 2D flow were reported.
Jordinson (1956) was the first to determine experimentally the trajectory of the jet, which is defined as the axis of the line joining the points of the maximum velocity and demonstrated that the cross-section of an initially cylindrical jet is distorted by the shear flow into a horseshoe shape. Gordier (1969) used the photographic techniques to geometrically determine the trajectories of jets of air-water mixtures discharging into a water channel. Keffer and Baines (1963) used oil-vapour and nitrogen aerosol for the qualitative visual investigations of an air jet injected in a low velocity wind tunnel. From the experimental observations, Pratte and Baines (1967) established the equation of jet trajectory in terms of the flow variable.
y ( / )B A x RD
RD = (2.1) Where D is the diameter of jet and A = 2.05, B = 0.28. Fan (1967) introduced the effect of a stratified atmosphere and suggested a mathematical model based on the resistance caused by the smoke jet in the flow. Abramovich (1967) established the expression for circular jets discharged at oblique angles into the crossflow using the empirical method. Platten and Keffer (1968) suggested a model taking into consideration of the two entrainment effects occurring in a deflected jet.
There have been numerous investigations on the jet in crossflow leading to the perception that the flow fields of jet in crossflow possess some difficulties in contrast to other flows like free jets and mixing layers. One main difficulty is that the flow field cannot be described in terms of its self similarity and Reynolds number dependence, due to the strong nonlinear effects. The systematic analysis of the jet in crossflow started in 1970s with the discovery and acceptance of coherent structures that are able to explain various nonlinear effects in the flow field of jet in crossflow.
The majority of the studies reported in the 1970s and 1980s were motivated by V/STOL related applications and several flow visualization and experimental studies (Mcmahon et al., 1971, Kamotani and Greber, 1971, 1972, Moussa et al., 1977, Fearn and Weston, 1978, Schetz, 1980, Rajaratnam and Gangadhariah, 1981, Foss, 1980,
Crabb et al., 1981, Andreopoulos and Rodi, 1984, Andreopoulos 1985, Sykes et al., 1986, Coelho and Hunt, 1989) were conducted to understand the characteristics of the jet-crossflow interactions. These studies exemplified the transverse jet dynamic effects by providing detailed experimental data on the mean and statistical characteristics of the flow field. Their measurement of axial velocity decay and the distribution of the turbulence intensity along the jet axis showed that the fluid entrainment and mixing process is more intensive for this flow field compared to that occurring in a free jet. The studies by Rajaratnam and Gangadhariah (1981) gave emphasis to the volume flux and entrainment characteristics of the deflected jets. The augmentation of entrainment was reflected by the larger entrainment velocity obtained in their investigation. A more complete survey was conducted by Crabb et al. (1981), who measured the mean and fluctuating velocity magnitudes with a Laser-Doppler anemometer near the jet exit and hot wires further downstream. The most referred work on jets in crossflow is that by Andreopouios and Rodi (1984), who reported a series of hot-wire measurements in the flow generated by a jet issuing from a circular outlet in a wall into a cross-stream along the wall and analyzed these in terms of the mean and turbulent flow characteristics. They commented on the extremely complicated nature of the flow in deflected jets, which they characterized by the ratio of the mean velocity in the jet orifice to a representative velocity of the crossflow.
Andreopoulos and Rodi (1984) identified two pairs of trailing contra-rotating vortices with opposite senses of rotation, a dominant primary pair bound within the deflected jet and a weaker secondary pair close to the wall in the wake of the jet, the bound pair having upflow through the centre of the jet and the wall pair having central downflow.
This topographical description of the deflected jets was valuable, but Andreopoulos and Rodi (1984) were unable to provide any satisfactory explanation of the flow structure.
After 1990s, the attention of researchers has shifted towards the characterization of the organized large-eddy motions (coherent structures) of this flow by means of flow visualization, numerical simulation, and pattern recognition analysis of hot-wire data.
Specific studies such as area-wise (near- and far-fields) investigations are made.
Several experimental studies have been reported in the literature dealing with the flow near the jet exit region and the effects of different parameters on the penetration of the jet (Licinsky, et al., 1996, Haven and Kurosaka, 1997, Zaman and Foss, 1997). The flow visualization studies include the visualization of the wake (Fric and Roshko,
1994) and of the counter-rotating vortex pair (Morton and Ibbetson, 1996, Blanchard et al., 1999). Along with accurate experimental techniques, advanced turbulence models such as direct numerical simulation (DNS) and large eddy simulation (LES) are also used to investigate the flow configuration. Rudman (1996) performed the first direct numerical simulation to predict the time-dependent behavior of a weakly compressible axisymmetric jet exiting normally into a crossflow. Yuan et al. (1999) used LES to study turbulent flow conditions. Eiff et al. (1995) and Eiff and Keffer (1997) used the pattern recognition to study the coherent structures in a jet in crossflow issuing from an elevated exhaust stack. They observed that the wake behind the stack synchronizes with the pseudo-wake of the jet and that some sort of structural connection exists in the far-field between the pseudo-wake and the jet core.
In the present decade (from the year 2000 till date) the number of reported investigations of this flow configuration is quite encouraging. The number of investigations reported in the literature using the advanced experimental techniques such as particle image velocimtery (PIV) and advanced turbulence models such as DNS and LES is continuously increasing with time. Most of the studies deal with the advanced analysis of unsteady flow field, vortex evolution, mixing enhancement and scalar distribution in the flow field. Some important works are reported by Hale et al.
(2000), Hoda and Acharya (2000), Kassimatis et al. (2000), Walter and Leylek (2000), Zhang (2000), Cortelezzi and Karagozian (2001), Keimasi and Rahni (2001), Lim et al. (2001), Rivero et al. (2001), Kalita et al. (2002), Peterson and Plesniak (2002), Johnston et al. (2002), New et al. (2003), Kolar et al. (2003), Naraynan et al.
(2003), Said et al. (2003), Shi et al. (2003), New et al. (2004), Su and Mungal (2004), Sau et al. (2004), Peterson and Plesniak (2004), Wegner et al. (2004), Pathak et al.
(2005), Said et al. (2005), Plesniak and Cusano (2005), Yang and Wang (2005), Mupidi and Maheshan (2005), Guo et al. (2006), Shan and Dimotakis (2006), Jovanovic et al. (2006), Majander and Siikonen (2006), Pathak et al. (2006), Muppidi and Mahesh (2007) and Pathak et al. (2007).