# Low-Pressure Turbine Cooling Systems

## Definition

**:**

## 1. Introduction

_{2}emissions are also achievable by reduction of fuel consumption. Exhaust gas temperature (EGT) may be lowered by ~10 °C through the reduction of tip clearances by 0.010 in. The main reason for the removal of an aircraft engine from service is the deterioration of the EGT margin. Up to 1000 extra cycles of engine on-wing time may be achieved by operating it at lower temperatures, thus increasing the life of hot sections parts. Other advantages are an increase in payload and mission range.

## 2. Basic Design Principle

## 3. ACC Operation Rationales

## 4. Heat Transfer between Casing and Air Stream from ACC

_{w}) and fluid temperature (T

_{j}). The value of Nusselt number Nu is given by the equation:

_{w}—wall temperature;

_{j}—nozzle temperature;

- -
- nozzle height to nozzle diameter (H/D);
- -
- distance between nozzle and target plate to nozzle diameter (Y/D);
- -
- distance between neighboring nozzles to nozzle diameter (S/D);
- -
- distance from jet axis to nozzle diameter (r/D);
- -
- Reynolds number according to the following expressions:

_{o}—mean nozzle velocity at the exit area;

- -
- Mach number based on nozzle exit average velocity (for the Ma < 0.3, there is a negligible impact on heat transfer rates)

_{t}—total pressure;

_{d}—static pressure;

_{t}—total temperature.

## 5. Review of Basic Geometrical and Physical Cooling Systems’ Parameters

## 6. Numerical and Experimental Methods of ACC Researches

_{w}) is measured with non-contact optical devices such as infrared (IR) thermography cameras or thermochromic liquid crystals that change their color with the temperature. The surface heat transfer coefficient (h) is calculated with the equation [9]:

## 7. Conclusions

## Funding

## Conflicts of Interest

## Entry Link on the Encyclopedia Platform

## References

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**Figure 1.**Schematic section of low-pressure turbine equipped with Active Clearance Control (ACC) [2].

**Figure 2.**Typical tube design of the ACC Cooling system of low-pressure (LP) and high-pressure (HP) turbines [3].

**Figure 4.**Distribution of velocity vectors in the x-y plane in the area of four cooling nozzles depicting the generation of fountain effect [10].

**Figure 6.**Tip clearance control [2].

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Marzec, K.
Low-Pressure Turbine Cooling Systems. *Encyclopedia* **2021**, *1*, 893-904.
https://doi.org/10.3390/encyclopedia1030068

**AMA Style**

Marzec K.
Low-Pressure Turbine Cooling Systems. *Encyclopedia*. 2021; 1(3):893-904.
https://doi.org/10.3390/encyclopedia1030068

**Chicago/Turabian Style**

Marzec, Krzysztof.
2021. "Low-Pressure Turbine Cooling Systems" *Encyclopedia* 1, no. 3: 893-904.
https://doi.org/10.3390/encyclopedia1030068