In modern gas turbine engines, the continuous increase of power for an expected lifetime has resulted in a continuous increase of cycle pressure ratio and turbine inlet temperature. The later implies that advanced materials and cooling techniques must be adapted for a safe operation of the high pressure gas turbine blades and vanes. This need for high power and high efficiency gas turbine engines forces the designer to continuously increase the turbine inlet temperature. In recent military applications, the turbine inlet temperature could be as high as 2000K, far above the melting temperature of the most advanced vane and blade materials. Thus apart from the progress made in the metallurgical domain, a continuous cooling of blade of turbine 1st stages allows operating at temperatures which are far above material’s melting point without affecting component integrity and geometry. The efficiency of the blade cooling system is therefore strictly related to the safe operation of the engine and complete understanding of the convection mechanisms resulting from the cooling techniques is mandatory. The most common internal heat transfer enhancement methods of heat transfer augmentation in gas turbine airfoils are ribs, pins, jet impingement, and flow disturbing inserts.To maintain the flow inside the cooling passage of turbine blade turbulent all these methods can be used. These devices act to increase turbulent mixing through the enhancement of turbulence.

1. RIB ROUGHENED COOLING
PASSAGES FOR TURBINE
BLADE COOLING
SEMINAR II
By: DEVI ARCHANA DAS

2. 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

3. 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.

4. 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

5. 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

6. RIBS INSIDE TURBINE BLADE

7. THE PHENOMENA OF RIBBED CHANNEL

8. TURBULENCE INTENSITY CONTOUR

9. 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.

10. 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.

11. DRAWBACKS
Industrial geometry optimization
Pressure losses are high .
Engine efficiency decreases.
Problem of CFD modelling.

12. THANK YOU