Experimental and numerical study on the effects of shaped multi-holes on the effectiveness of film cooling
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Experimental and numerical study on the effects of shaped multi‑holes on the effectiveness of film cooling Yaser Taheri1 · Mehran Rajabi Zargarabadi1 · Mehdi Jahromi2 Received: 24 January 2020 / Accepted: 4 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In the present work, experimental and numerical study has been performed to investigate the effects of a novel film-cooling design with shaped multi-holes on the film-cooling effectiveness over a flat plate. A single cylindrical hole with 11.1 mm diameter has been replaced by multi-holes (14 holes with 2.97 mm diameter) with elliptical and fan-shaped configurations. The exit area, length to diameter ratio (L/D = 4.0) and injection angle (35°) of multi-holes are selected identical to the single cylindrical hole. The multi-holes were machined with a fixed spacing pitch (33.3 mm) between the centers of two adjacent holes. The surface temperature of the test plate was measured by an infrared camera. The experimental studies were performed at blowing ratios of 0.5 and 2. The numerical results based on the steady RANS with realizable k–ε turbulence model and enhanced wall treatment were capable to predict the influence of the shape of multi-hole configurations on overall adiabatic film-cooling effectiveness. The experimental and numerical results showed that replacing a single hole with a shaped multi-hole leads to a considerable increase in film-cooling effectiveness in both axial and lateral directions. According to the results at blowing ratio of 2.0, the elliptical and fan-shaped configurations provide a higher area-averaged film-cooling effectiveness by 75% and 248.2% in comparison with the single hole, respectively. Keywords Experimental study · Film cooling · Multi-holes · Adiabatic effectiveness Abbreviations M Blowing ratio = (𝜌U)c ∕(𝜌U)∞ T Temperature (K) Tu Turbulent intensity (%) x/D Non-dimensional streamwise distance DR Coolant to free-stream density ratio = 𝜌c ∕𝜌∞ D Diameter of the hole (mm) k Turbulent kinetic energy (m2 s−2) L Length of the hole (mm) Re Reynolds number Greek symbols β Streamwise injection angle (°) Θ Internal energy (J) θ Heat flux (W m−2) ε Dissipation rate of turbulent kinetic energy (m2 s−3)
* Mehran Rajabi Zargarabadi [email protected] 1
Department of Mechanical Engineering, Semnan University, Semnan, Iran
Malek Ashtar University of Technology, Tehran, Iran
2
η (eta) Adiabatic film-cooling effectiveness; 𝜂 = ρ Density of the fluid (kg m−3) τ w Wall shear stress (kg m−1 s−2) μ Dynamic viscosity (kg m−1 s−1) μt Turbulent dynamic viscosity (kg m−1 s−1)
Taw −T∞ Tj −T∞
Subscripts j Jet ∞ Free stream aw Adiabatic wall
Introduction One of the effective methods for enhancing the engine power and thermal efficiency of modern gas turbines is the increase of turbine inlet temperature, although, due to thermal stresses, this method may lead to the failure of high-temperature components. Hence, for the cooling of gas turbines external and internal cooling techniques are used. Amon
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