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