Leading Edge Impingement With Racetrack Shaped Jets and Varying Inlet Supply Conditions

Abstract

Impinging jets are often employed within the leading edge of turbine blades and vanes to combat the tremendous heat loads incurred as the hot exhaust gases stagnate along the exterior of the airfoil. Relative to traditional cylindrical jets, racetrack shaped impinging jets have been shown to produce favorable cooling characteristics within the turbine airfoil. This investigation experimentally and numerically quantifies the cooling characteristics associated with a row of racetrack shaped jets impinging on a concave, cylindrical surface. Detailed Nusselt number distributions are obtained using both a transient liquid crystal technique and commercially available CFD software (Star CCM+ from CD-Adapco). Three geometrical jet inlet and exit conditions are experimentally investigated: a square edge, a partially filleted edge (r/dH,Jet = 0.25), and a fully filleted edge (r/dH,Jet = 0.667). Additionally, to investigate the effect of high crossflow velocities at the inlet of the jet, a portion of the flow supplied to the test apparatus radially bypasses the impingement section. Thus, the mass flow rate into the test section is varied to achieve the desired inlet crossflow conditions and jet Reynolds numbers. As a result, jet Reynolds numbers (ReJet) of 11500 and 23000 are investigated at supply duct Reynolds numbers (ReDuct) of 20000 and 30000. The results are compared to baseline cases where no mass bypasses the test section. Additionally, the relative jet – to – jet spacing (s/dH,Jet) is maintained at 8, the relative jet – to – target surface spacing (z/dH,Jet) is 4, the target surface curvature – to – jet hydraulic diameter (D/dH,Jet) is 5.33, and the relative thickness of the jet plate (t/dH,Jet) is 1.33. Measurements indicate that the addition of fillets at the edges of the jet orifice and the introduction of significant crossflow velocity at the inlet of the jet can significantly degrade the cooling characteristics on the leading edge of the turbine blade. The magnitude of such degradation generally increases with increasing fillet size and inlet crossflow velocity. The V2F model is adequate for predicting the flow field and target surface heat transfer in the absence of inlet crossflow; however, it is believed the turbulence within the jet is overpredicted by the CFD leading to elevated heat transfer coefficients (compared to the experimental results).

Turbine Blade Leading Edge Impingement Cooling From Normal or Tangential Jets With Crossflow Effect

“…Attalla (2005) found that the jet-to-target surface spacing, z/d, has a negligible effect on the heat transfer when 2 ≤ z/d ≤ 5 for multiple jets. Taslim et al (2001b) and Jordan et al (2012Jordan et al ( , 2013Jordan et al ( , 2016 reported that racetrack shaped jet holes provided higher heat transfer coefficients than the round jet holes at the same flow condition. Van Treuren et al (1996) compared the local and average heat transfer coefficients between inline and staggered impinging arrays.…”

Effect of Rotation and Hole Arrangement in Cold Bridge-Type Impingement Cooling Systems

“…Jet supply condition is also relevant for system performance. In cooling systems where the impingement plate is fed by a cavity with a radial crossflow, a residual component of radial momentum can be transported inside the impingement hole and then into the LE cavity: the cooling jet is thus bent towards the radial direction, reducing the heat transfer [8,9]. However, the reduction of the apparent hole cross-section can enhance jet lateral spreading, thus increasing wall-jet interaction and compensating heat transfer degradation [10,11].…”

Conjugate Heat Transfer Study at Interior Surface of NGV Leading Edge with Combined Shower Head and Impingement Cooling

“…Li et al [14] have studied the effect of arrangement of film holes on impingement heat transfer and concluded that the hole position of film cooling holes significantly affects the shape of high heat transfer area and Nu in stagnation zone decreases with the increase of array angle of film cooling holes. Jordan et al [15] have found out that the addition of fillets at the edges of the jet orifice and the introduction of significant cross flow velocity at the inlet of the jet can significantly degrade the cooling characteristics on the leading edge of the turbine blade. Mehendale and Han [16] used a cylindrical model with two rows of film holes for studying the effect of Reynolds number and film hole spacing on the adiabatic effectiveness.…”