RIB ROUGHENED COOLING PASSAGES FOR TURBINE BLADE COOLING
SEMINAR IIBy: DEVI ARCHANA DAS
NEED FOR BLADE COOLING
Requirement of modern gas turbines for high power and high efficiency
Designer needs to continuously increase Turbine Inlet temperature
Metallurgical advancements are not sufficient to meet the requirements
GENERAL HEAT TRANSFER TECHNIQUES
Generally blades are cooled by external film cooling which limits heat flux from the combustion gases and internal convection.
Impingement cooling extracts the heat from blade material.
Requirement is to maintain the flow inside the cooling passage as turbulent as possible.
HEAT TRANSFER TECHNIQUES FOR ADVANCED COOLING
Several heat transfer techniques can be used to increase the heat transfer coefficients internally, namely:
Ribs
Pins
Jet impingement
Flow disturbing inserts
WHAT ARE RIBS ?
Ribs are turbulence promoting structures that accelerate the flow through:
Enhancement of turbulence
Generation of secondary flows
Production of stream wise oriented structures
RIBS INSIDE TURBINE BLADE
THE PHENOMENA OF RIBBED CHANNEL
TURBULENCE INTENSITY CONTOUR
HOW A RIBBED CHANNEL WORKS ?
The presence of obstacle by a significant blockage ratio reduces the available cross section.
Induces strong acceleration in the flow field.
Sudden expansion downstream of the rib; leading to flow separation is due to strong shear layer.
INFERENCES
If the jet is placed in between two ribs, higher Nusselt number is obtained rather than other positions of the jet.
Heat transfer coefficients increase with jet to target plate spacing.
Forced convection cooling is significantly enhanced in presence of ribs.
DRAWBACKS
Industrial geometry optimization
Pressure losses are high .
Engine efficiency decreases.
Problem of CFD modelling.
THANK YOU
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