Labyrinth Seal

Summary

The video script explains the function of a labyrinth seal in various mechanical systems, particularly in engine bearings and turbine interstages. It describes how the seal, composed of fins or knife edges, maintains oil tightness by utilizing pressure differences to prevent oil mist leakage. The script also covers the importance of equal oil distribution to each jet and the necessity of a larger scavenge system to handle the aerated, expanded oil resulting from the labyrinth seal's operation.

Takeaways

• 🔧 A labyrinth seal is made up of a series of fins or knife edges that create a minimum clearance with the lining upon initial engine operation.
• 💨 Pressurized air from the bleed air system is used to create a pressure drop across the fins, establishing a high-pressure and a low-pressure area.
• 🌫️ The oil mist created by the interaction between the oil and the hot bearing is prevented from seeping out due to the pressure differential, keeping the compartment oil-tight.
• 🛠️ The labyrinth seal is not airtight, allowing air to pass but preventing oil leakage, which is crucial for the operation of the engine.
• 📏 The scavenge system must have a larger capacity than the pressure system to handle the increased volume of aerated, warm oil.
• 🔄 The venting of compartments ensures equal pressure distribution, which is necessary for equal oil supply to each jet.
• 🛡️ The labyrinth seal is also used in interstage applications, such as in turbine areas, to prevent hot gases from reaching the bearings.
• 🌡️ The seal helps to manage temperature by creating a pressure gradient that directs gases away from sensitive components.
• 🔄 The design of the labyrinth seal involves a balance between maintaining oil tightness and allowing for air flow necessary for engine operation.
• 🛑 The seal's effectiveness relies on the precise interaction between the fins, the pressure system, and the scavenge system.
• 🔧 The labyrinth seal's knife edges are a critical component in maintaining the seal's functionality and preventing leakage.

Q & A

What is a labyrinth seal?

A labyrinth seal is a type of mechanical seal that consists of a series of fins or knife edges designed to prevent leakage, typically used in rotating machinery such as engines or turbines.

How does a labyrinth seal function in an engine?

In an engine, the labyrinth seal's fins lightly rub against the lining during initial running, cutting into it to create minimum clearance. Pressurized air from the bleed air system bleeds across the fins, creating a pressure drop that helps maintain oil tightness while allowing air to pass for cooling.

Why is oil mist created in the labyrinth seal?

Oil mist is created when the oil sprayed onto the hot bearing from the pressure pump turns into mist due to the heat. The pressure difference created by the labyrinth seal causes the oil mist to stay within the compartment due to the natural tendency of gases to move from high to low pressure areas.

What is the purpose of the pressure drop in a labyrinth seal?

The pressure drop in a labyrinth seal helps to maintain an oil-tight environment by creating a low-pressure area that prevents the oil mist from seeping out past the seal, while still allowing air to flow for cooling purposes.

How does the oil get warmed and expand in the labyrinth seal?

The oil gets warmed when it hits the hot bearing, causing it to expand. This warm, expanded oil then moves to the bottom of the compartment, where it mixes with the air that has leaked past the seal, creating aerated oil.

Why is the scavenge system capacity larger than the pressure system?

The scavenge system capacity must be larger to handle the increased volume of aerated oil, which can be up to three times the volume of the pressurized oil due to the expansion from heat and the mixing with air.

What is the role of vents in the labyrinth seal compartments?

Vents in the labyrinth seal compartments ensure equal pressure between different compartments, which is important for distributing oil evenly to each of the jets or bearing areas.

How does an interstage seal in a turbine work?

An interstage seal in a turbine works by using the pressure drop created by bleed air passing across the seal edges to prevent hot gases from leaking towards the bearings. The adverse pressure gradient discourages the gases from moving from a low-pressure to a high-pressure area.

Why is it important to keep hot gases away from the bearings in a turbine?

Keeping hot gases away from the bearings is crucial to prevent overheating and potential damage to the bearings, as the hot gases from combustion can be very warm and may affect the performance and longevity of the machinery.

What are some applications of labyrinth seals other than in bearing compartments?

Labyrinth seals can be used in various applications where leakage prevention is required. One such application is in interstage seals within turbines, where they help to prevent hot gases from reaching sensitive components.

Outlines

00:00

🔧 Labyrinth Seal in Engine Bearings

The first paragraph discusses the function and design of a labyrinth seal in an engine bearing. It explains that the seal consists of a series of fins or knife edges that initially rub against the lining to create a minimum clearance. Pressurized air from the bleed air system enters and bleeds across the fins, creating a pressure drop that results in a high-pressure area outside and a low-pressure area inside. This design prevents oil mist from seeping out due to the pressure difference, making the compartment oil-tight but not airtight. The oil, warmed by the bearing, expands and creates an aerated oil mixture, necessitating a scavenge system with a capacity multiple times greater than the pressure system. The paragraph also touches on the importance of equal oil supply to each jet and the venting of compartments to maintain equal pressure.

05:01

🌀 Interstage Seal in Turbine Applications

The second paragraph explores the use of labyrinth seals in turbine applications, specifically as interstage seals. It describes how bleed air passing through the turbine blades and nasal guide vanes creates high and low-pressure areas that prevent hot gases from leaking towards the bearings. The seal's design ensures that the warm air from combustion, which can be detrimental to the bearings, is kept away. This interstage seal is another example of how labyrinth seals can be utilized to maintain pressure integrity in different components of machinery.

Keywords

💡Labyrinth Seal

A labyrinth seal is a mechanical seal that consists of a series of fins or knife edges. It is designed to prevent oil leakage while allowing air to pass through. In the context of the video, it is used in engine components to maintain oil tightness while permitting air flow. The script describes how the fins lightly rub against the lining during initial engine operation, creating a minimum clearance that helps in maintaining the seal's effectiveness.

💡Fins

Fins in the context of a labyrinth seal refer to the protruding elements that interact with the engine lining. They are crucial in creating the necessary clearance for the seal to function properly. The script mentions that these fins cut into the lining, ensuring a tight seal that prevents oil leakage.

💡Pressurized Air

Pressurized air in the script refers to the air that is forced into the system under pressure. It plays a role in maintaining the pressure balance within the engine components. The script explains how pressurized air enters the system and bleeds across the fins, creating a pressure drop that is essential for the proper functioning of the labyrinth seal.

💡Pressure Drop

Pressure drop is the decrease in pressure that occurs as air passes through the labyrinth seal's fins. It is a critical phenomenon in the operation of the seal, as it helps maintain the seal's effectiveness by creating a pressure differential. The script describes how high pressure air enters the system and, upon passing through the fins, results in a pressure drop that contributes to the seal's functionality.

💡Oil Mist

Oil mist is the fine spray of oil that is generated when oil is sprayed onto hot engine components. In the script, it is mentioned that the oil mist is influenced by the pressure differential created by the labyrinth seal. The high-pressure area outside the seal prevents the oil mist from escaping, thus keeping the engine compartment oil tight.

💡Bearing

A bearing in the context of the script refers to a mechanical component that supports and constrains movement in a mechanical system. The labyrinth seal is particularly relevant to the bearing compartment, as it helps in maintaining the oil tightness around the bearing. The script discusses how oil is sprayed onto the bearing and how the seal prevents oil leakage.

💡Scavenge System

The scavenge system is a component responsible for removing the aerated oil from the engine. It is crucial in managing the oil volume in the system, especially when the oil has expanded due to heat. The script mentions that the scavenge system needs to be capable of handling multiple times the volume of the oil supplied by the pressure system to account for the expanded oil and air mixture.

💡Interstage Seal

An interstage seal is a type of labyrinth seal used in turbines to prevent hot gases from leaking towards the bearings. The script explains how the interstage seal operates by creating a high-pressure area that discourages the movement of hot gases towards the lower-pressure area near the bearings, thus protecting the engine components.

💡Turbine Blades

Turbine blades are components in a turbine that rotate due to the flow of fluid or gas. In the script, they are mentioned in relation to the interstage seal, which is used to prevent hot gases from reaching the turbine blades and other components. The seal helps in maintaining the efficiency and safety of the turbine operation.

💡Nasal Guide Vanes

Nasal guide vanes are components in a turbine that guide the flow of gases towards the turbine blades. They are mentioned in the script in the context of the interstage seal, which helps in controlling the flow of gases and preventing them from leaking towards the bearings. The seal plays a crucial role in maintaining the proper operation of the nasal guide vanes.

💡Bleed Air

Bleed air is air that is taken from the engine's compressor and used for various purposes, such as cooling or pressurizing. In the script, bleed air is described as passing through the labyrinth seal, creating a pressure drop that is essential for the seal's operation. The bleed air system is integral to the functioning of the labyrinth seal in both bearing compartments and interstage seals.

Highlights

A labyrinth seal is comprised of a series of fins or knife edges.

Fins lightly rub against the lining on initial engine running, cutting into it to provide minimum clearance.

Pressurized air from the bleed air system is used to maintain the seal's functionality.

The pressure drop across the fins creates a high-pressure and a low-pressure area.

Oil mist is created when the oil hits the hot bearing, influenced by the pressure gradient.

The oil mist is prevented from seeping out due to the pressure gradient, making the compartment oil-tight.

The oil expands due to temperature increase when it hits the bearing.

The volume of aerated oil can be three times the volume of the pressurized oil.

The scavenge system must be multiple times larger than the pressure system to handle aerated oil.

Equal amounts of oil are supplied to each jet by venting the compartments to each other.

Labyrinth seals can be used in various applications, including bearing compartments and interstage seals.

In the turbine area, interstage seals prevent hot gases from leaking towards the bearings.

The adverse pressure gradient in interstage seals keeps air from moving from low to high pressure areas.

Labyrinth seals are crucial for keeping warm air from combustion away from sensitive components like bearings.

The labyrinth seal design ensures that air and oil are managed effectively in mechanical systems.

The design of labyrinth seals is critical for maintaining the integrity and performance of mechanical systems.

Understanding the pressure dynamics in labyrinth seals is essential for their effective application.

Transcripts

so here we have

this area here that is a

labyrinth type seal

and a labyrinth seal is comprised of a

series of fins

or our knife edges

on initial running of the engine the

fins

lightly rub against the lining so this

is the lining here

and it cuts into the lining giving

minimum clearance between the fins and

the lining

pressurized air from you know the bleed

bleed air system uh bleeds inwards

okay so it comes into the pressurized

air comes in here

let me just change the color

so pressurized air comes in

and then it bleeds across the fins

and as it bleeds across we get a

pressure drop so we

might just look at that more closely

so here is here the fins replicated

here's the the bleed air so

when the air comes through

and it passes these fins we get a

pressure drop so we get

high pressure here and low pressure

here so that means we have a low

pressure area in here

and a high pressure area here

and because of that the oil that comes

in from the

pressure pump that's sprayed onto the

bearing and

spray the high pressure and when the

the oil hits the hot bearing we will get

an oil mist

and that oil mist will say well there's

a high pressure

out here and we're in a low pressure

area and

you know gases want to go from high

pressure to low pressure

not from low pressure to high pressure

so the the mist of oil won't be able to

go this direction

okay it won't be able to seep out past

the seal

so the the compartment is

oil tight okay now it's not airtight

because air has to pass over it but it

is oil tight

the oil then

when it hits the the bearing it will

it would get warmer and will expand due

to that that

increase in temperature and that will

come to the bottom of the compartment

here

so down here we have the oil the warm

oil

and the air that has has leaked in past

the by the labyrinth seal

and that just creates an aerated oil and

the volume of this

could be you know three times the the

volume of the pressurized oil

so the scavenge system capacity

needs to be multiple times bigger than

the

pressure system so maybe three times

so if if the oil pressure system is

supplying

oil at let's say one

cubic meter per minute then

the scavenge system would have to take

out three cubic meters

of aerated oil because it's air and oil

and the oil is warm and so therefore it

has expanded

this is a an image of a labyrinth seal

and you can see the knife edges

here along along the seal

now when the oil comes in

um as i said we we we have a high

pressure area here and then we get a low

pressure area in here in the in

the compartment and that's a low

pressure area in this compartment

now we need to make sure that there's

equal amounts of oil

supplied to each of the jets so let's

assume that uh you know maybe this

chamber here was at a slightly higher

pressure than this

than this chamber over here but if this

was at a higher pressure

then less oil would want to go down here

and more oil would want to go down

through here so we wouldn't be getting

the same amount of oil

in each com compartment to offset

that the compartments are vented

to each other so we have a vent here an

event over here

and that ensures that we have equal

pressure in this chamber

to that chamber therefore we should be

getting equal amounts of oil

into into both chambers

all right so that's uh that's the

labyrinth seal

as applied to a bearing compartment or

bearing chamber

it can also be used in other

applications

and one such application is the

interstage seal

so here we have a turbine area so let's

these are the turbine blades and these

are the nasal guide vanes

and we have these interstage seals so we

would have

a bleed air coming through

and passing across the

edges like that and that creates a high

pressure area

in here and a low pressure area

just here so therefore the hot gases

when the hot gases come through

they'll come through and they'll see

um high pressure area here and they'll

say

no i just keep keep going through here

because due to this

adverse pressure gradient you know the

air won't want to go from a low pressure

area to a high pressure area so

the air will just go through here and

none of it will want to leak down

in towards where the bearings are and

remember this air coming

from the combustion can this is very

warm so we want to keep that away from

from the bearings and whatever else is

down along here

so that's an interstage seal it is

another example of a labyrinth type

seal