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Research Papers: Jets, Wakes, and Impingement Cooling

# Influence of Near Hole Pressure Fluctuation on the Thermal Protection of a Film-Cooled Flat Plate

[+] Author and Article Information
André Burdet

Gas Turbine Business, Alstom (Switzerland) Ltd., CH-5242 Birr, Switzerland

Reza S. Abhari

Laboratory of Energy Conversion (LEC), Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETHZ), CH-8092 Zürich, Switzerland

J. Heat Transfer 131(2), 022202 (Jan 05, 2009) (11 pages) doi:10.1115/1.2995651 History: Received February 23, 2008; Revised July 20, 2008; Published January 05, 2009

## Abstract

The pulsation of film cooling jets in turbines is driven by the near hole pressure fluctuation caused by the deterministic interaction of stator/rotor blade rows. Jet pulsation is characterized by the coolant near hole reduced frequency $Ωc$ and the pulsation amplitude coefficient $Ψ$. The fluctuation of the near hole pressure is simulated by setting a time-varying signal of static pressure for the outlet boundary condition of a film-cooled flat plate configuration. It is observed that the fluctuation of the near hole pressure influences the blowing ratio, hence the thermal protection downstream of the injection site. For a low mean blowing ratio $(BR¯=0.75)$, low-medium pulsation frequencies $(Ωc⩽0.10)$ are found to be slightly detrimental to the thermal protection versus a steady injection. On the contrary, for high pulsation frequencies $(Ωc⩽0.17)$, the thermal protection becomes better due to periodic jet disintegration into the wall surface caused by a higher level of transverse kinetic energy of the jet pulse. In addition, the overlapping of jet pulses appears to help the constant temporal spreading of coolant over the wall surface. For a higher mean blowing ratio $(BR¯=1.25)$, jet pulsation enhances lift-off so that the thermal protection is, in general, worse compared to a steady injection. Overall, the range of jet pulsation presented in this study affects moderately the thermal protection of the downstream surface.

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## Figures

Figure 4

Predicted time-averaged laterally averaged wall adiabatic film cooling effectiveness for all pulsation frequencies investigated. BR¯=0.75 (left) and BR¯=1.25 (right).

Figure 1

Concept of large-scale pressure fluctuation in the near hole region. The pressure signal is taken from measurements of Haldeman (15).

Figure 2

Near hole jet model embedded in its three-dimensional film cooling grid box at time t (left) and later at time t+Δt (right). Dots show the plane of injection and the jet surface. The flat plate surface area is covered by predicted contours of static pressure.

Figure 3

Recorded near hole pressure Ps from the numerical solution and related instantaneous blowing ratio BR¯ as a function of time for BR¯=1.25

Figure 5

Space-time diagram of the predicted total temperature TT contours on the center plane y∕d=0 (top left) on three cross planes x∕d=[4,10,15] (right, with cross velocity vectors) and the predicted effectiveness η on the flat plate z∕d=0 (bottom left) for four equally spaced time steps. BR¯=0.75 and Ωc=0.04(F=200Hz).

Figure 6

Space-time diagram of the predicted total temperature TT contours on the center plane y∕d=0 (top left) on three cross planes x∕d=[4,10,15] (right, with cross velocity vectors) and the predicted effectiveness η on the flat plate z∕d=0 (bottom left) for four equally spaced time steps. BR¯=0.75 and Ωc=0.17(F=800Hz).

Figure 7

Space-time diagram of the predicted total temperature TT contours on center plane y∕d=0 (top left) on three cross planes x∕d=[4,10,15] (right, with cross velocity vectors) and the predicted effectiveness η on the flat plate z∕d=0 (bottom left) for four equally spaced time steps. BR¯=0.75 and Ωc=0.67(F=3200Hz).

Figure 8

Space-time diagram of the predicted total temperature TT contours on the center plane y∕d=0 (top left) on three cross planes x∕d=[4,10,15] (right, with cross velocity vectors) and the predicted effectiveness η on the flat plate z∕d=0 (bottom left) for four equally spaced time steps. BR¯=1.25 and Ωc=0.03(F=200Hz).

Figure 9

Space-time diagram of the predicted total temperature TT contours on the center plane y∕d=0 (top left) on three cross planes x∕d=[4,10,15] (right, with cross velocity vectors) and the predicted effectiveness η on the flat plate z∕d=0 (bottom left) for four equally spaced time steps. BR¯=1.25 and Ωc=0.10(F=800Hz).

Figure 10

Space-time diagram of the predicted total temperature TT contours on the center plane y∕d=0 (top left) on three cross planes x∕d=[4,10,15] (right, with cross velocity vectors) and the predicted effectiveness η on the flat plate z∕d=0 (bottom left) for four equally spaced time steps. BR¯=1.25 and Ωc=0.40(F=3200Hz).

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