Conjugate Heat Transfer Predictions of Gas Turbine Hot Walls Jets Cooling: Influence of Short Hole Grid Resolutions Using Computational Fluid Dynamics*
Short hole investigations relevant to gas turbine (GT) hot walls cooling
heat transfer techniques, were carried out using computational fluid dynamics
(CFD) combined with conjugate heat transfer (CHT) code. The CFD software are
commercial ones: ICEM for grid modelling and ANSYS Fluent for the numerical
calculation, where symmetrical application prevails. The CFD CHT predictions
were undertaken for Nimonic-75
metal walls with square (152.4 mm) arrays of 10 holes, whereby the lumped heat
capacitance method was applied in order to determine the surface average heat
transfer coefficient (HTC), h (W/m2 K) and the dimensionless Nusselt number, Nu.
The major parameters considered for the short hole geometries are the pitch to
diameter, X/D and length to diameter, L/D ratios and both were varied with range
of D values, but X of 15.24 mm and L of
6.35 mm kept constant. Also applied, are variable mass flux, G (kg/s∙m2) and were used in
predicting the flow aerodynamics in the short holes. The predictions were for
classic thermal entry length into a round hole, as vena contracta, flow
separation and reattachment dominates the holes, hence the development of
thermal profile through the depth of the GT hot walls. Additionally, the
acceleration of the flow along the wall surfaces as it approaches the holes,
was a significant part of the overall heat transfer. This was shown to be
independent of the hole length, even though the L/D parameter is a
critical component to enhanced heat transfer. The CFD CHT predictions showed
that validation of the HTC h, Nu and pressure loss, ∆P are in better agreement with measured
data and within reasonable acceptance. The ∆P agreement signifies that the aerodynamics were predicted correctly, which is
also the reason why the HTC expressed per wall hole approach surface area and Nu were better predicted. This
illustrates how
effective and
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