Labyrinth Seal
Summary
TLDRThe 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
🔧 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.
🌀 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.
Mindmap
Keywords
💡Labyrinth Seal
💡Fins
💡Pressurized Air
💡Pressure Drop
💡Oil Mist
💡Bearing
💡Scavenge System
💡Interstage Seal
💡Turbine Blades
💡Nasal Guide Vanes
💡Bleed Air
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
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