Thermal Development of an Impinging Jet Using Planar Laser Induced Fluorescence (PLIF)

Planar Laser Induced Fluorescence (PLIF) has been demonstrated to investigate a round jet impinging on a flat surface. Detailed thermal field distributions have been obtained near the flat target surface to characterize the wall jet development ensuing from the stagnation point. While PLIF has been demonstrated for combustion applications to measure concentration gradients within a mixture, its application for temperature field measurements is less established. Therefore, the technique was applied to a simple, cylindrical impinging jet. The jet Reynolds number varied with Rejet = 5,000–15,000 while the jet–to–target surface spacing varied from H / D = 4–10. The cooling jet (Tjet ∼ 300 K) impinged on a flat, heated surface. The PLIF technique was able to capture the free jet structure and jet development along the target surface. With a short impingement length (H / D = 4), the potential core of the jet strikes the target surface. The thermal gradients captured during the experiments demonstrate the fully turbulent nature of the impinging jet with H / D = 10. The thermal boundary development along the target surface is clearly captured using this fluorescence method. The near wall temperature gradients acquired with the PLIF method have been used to calculate heat transfer coefficients on the heated surface, and these values compare favorably to those measured using a well-established steady state, heat transfer method. The PLIF technique has been demonstrated for this fundamental impingement setup, and it has proven to be applicable to more complex heat transfer and cooling applications.