Gas Turbine Cooling System Design Procedures

Introduction

State-of-the-art gas turbine engines usually work under extremely high temperatures. This is directly related to efficiency of the gas turbines – in order to receive the maximum thermodynamics value, it is necessary to increase the gas temperature after the combustion chamber. Engine temperature can be higher than blades’ metal temp up to 500-600 K. Blades, nozzles, and the GT details are manufactured with special heat-resistant steels and in some cases, they require a special coating. That allows them to resist turning into liquid metal under these working temperatures like the T-1000 did in the “Terminator 2: Judgment Day” movie even under high temperatures :).

Picture 1 – T-1000 from Terminator 2
Picture 1 – T-1000 from Terminator 2. Source

However, metal has the property of “creep” – this is the tendency of hard metal to move slowly or permanently deform under stress. This occurs as a result of prolonged exposure to high stresses above the yield point, especially when exposed to high temperatures. Obviously, the solution to this problem is a cooling system for heat-stressed parts, which has allowed the gas temperature to increase by 600 K compared with uncooled machines. Since the gas turbines usually work with air, the simplest way to cool the system is by using this. Typically, the air exhausts to different parts of the compressors and is supplied to the cooling paths and blades which influence the thermodynamics efficiency of the gas turbine engine. Thus, it is crucial to ensure enough cooling to remove the heat on the one hand and on the other hand – to receive the lowest amount of air which requires cooling. Read More

Aircraft Life Support Systems Part 2: Water and Waste System

INTRODUCTION

In the aircraft industry, several systems are designed to provide safety and comfort for the crew and passengers.

Regarding comfort, the water and waste system is designed to provide water for galleys and lavatories. Fresh water is stored and distributed while a different system deals with wastewater. That system includes a thoughtful engineering method to dispose of the different wastes that could occur during the flight.

OVERVIEW

Water must be supplied to different parts of the plane during flight. This water is kept in a tank in the compartment aft of the bulk cargo compartment. The whole system is made up of a passenger water system that stores, delivers, monitors and controls drinkable (potable) water for the galley units and lavatory sink basins.

In this blog, we are going to focus more specifically on the 737-classic model from Boeing.

Figure 1-Representation of different parts of the water and waste system
Figure 1-Representation of different parts of the water and waste system

The 3 main achievements of the water and waste system are the following:

  • Filling the water tank on land
  • Providing water during the flight
  • Storing toilet waste

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The water and waste system is made up of:

  • Potable water system aims to deliver fresh water to every needed part in the plane (including every component between the water tank and sinks)
  • Water tank pressurization system focuses on the pressurization of the water tank and air dealing with the tank (including air compressor, pressure regulator filter, pressure relief valve)
  • Wastewater system focuses on water related to lavatory and sinks / galleys wastewater (including drain masts)
  • Toilet system includes components related to flushing and toilet water (including waste tank)

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The water tank has a capacity of 34 gallons (about 0.15 m3). The water system in the plane needs to be pressurized for altitude just like the cabin, so it gets pressurized by an air inlet (linked to the pneumatic system). Therefore, the water quantity should not exceed 30 gallons (about 0.13 m3). Read More

Aircraft Life Support Systems Part 1: Oxygen System

INTRODUCTION

In the aircraft industry, several systems are designed to provide safety and comfort for crew and passengers while traveling. Oxygen gets rarified with altitude, so life support is a very important system

The cabin is pressurized in order to provide breathable air, but reaching a sea level pressure is not advisable since it would lead to a significant pressure differential between the aircraft exterior and the cabin interior. This difference could damage the aircraft structure.

Additionally, the cabin altitude is different from the flight altitude. In fact, the cabin altitude corresponds to the one reached according to the cabin pressure. Usually a commercial flight cruises at an altitude of 35,000 ft, but thanks to the pressurization system, the cabin altitude is around 6,000-8,000 ft.  Indeed, the oxygen system provides breathable oxygen to the crew and passengers if any problem were to occur during the flight.

AIRCRAFT EMERGENCY OXYGEN SYSTEM:

In a normal situation, a bleed air system is used to provide fresh air throughout the flight duration. The air is hot and must be cooled and pressurized to make it breathable.  In the event of an emergency, the plane is already equipped with oxygen systems which are linked to passengers and cabin crew through masks. In fact, there are two oxygen systems on board. One designed for the crew, and the second for the passengers.

If the cabin pressure drops making cabin altitude about 14,000 ft, the emergency system are be triggered. The emergency system provides oxygen to passengers for 15 to 20 minutes, and for the crew members for around 30 minutes. This is enough time for the aircraft to descend to a lower altitude and being the cabin altitude to a safe breathable level.

Here, the crew oxygen system schematic of the Boeing 737 class is shown in Figure 1.

Figure 1-Crew oxygen system
Figure 1-Crew oxygen system

The main challenges of oxygen equipment are:

  • Fitting the dimensions of the plane
  • Secure (no leakage for example)
  • Responsive (to cabin pressure and cabin altitude)
  • Easy for passengers to use the oxygen system through the deployed masks quickly, before the effects of altitude are felt:
  • At 25,000 ft: a person has 3 minutes of consciousness
  • At 41,000 ft: a person has 30 seconds of consciousness

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FLIGHT CREW OXYGEN

The flight crew oxygen should be designed and made with a lot of care, because if any trouble occurs during the flight, the crew must be able to handle the situation and take the airplane and its passengers down safely. Read More

Performance Testing of Axial Compressors

Performance testing is a key part of the design and development process of advanced axial compressors.  These are widely used in the modern world and can be found in nearly every industry, and include the core compressor for aeropropulsion turbofan engines, as well as aeroderivative gas turbine engines for power generation.  An example of this are the turbine engines shown in Figure 1 and 2, which feature an industrial gas turbine and a high bypass ratio turbofan engine with a multistage high-pressure core compressor. The development time of these machines can involve numerous expensive design-build-test iterations before they can become an efficient and competitive product. This places a great importance on the accuracy of the data taken during the performance tests during the development of the compressor since the test data taken is often used to anchor the loss models within the design tools. Modern axial compressors typically have high aerodynamic loadings per stage for improved system efficiency and requires precise aerodynamic matching of the stages to achieve the required pressure ratio with high efficiency. Variable geometry inlet guide vanes and stators in the first few stages are typically required to provide acceptable operability while maintaining high efficiency and adequate stall margin.

Industrial gas turbine for power generation.
Figure 1. Industrial gas turbine for power generation. Source
Figure 2. Turbofan engine for aeropropulsion.
Figure 2. Turbofan engine for aeropropulsion. Source

Performance Testing of Axial Compressors

Axial compressors all undergo a thorough design and development phase in which performance testing is vital to their ultimate success as a product. Performance testing during the development phase of these high-power density machines can ensure that the design meets the specified requirements or can identify a component within the turbomachine which falls short of its expected performance, and may require further development, and possible redesign. Performance testing can also ensure that the unit can meet all the conditions specified and not merely the guaranteed condition. Aerodynamic performance testing multistage axial compressors during the early part of development is often done in phases. The development test program is planned and executed with a design of experiments approach and includes varying the air flow and shaft rotational speed as well as the variable geometry schedule in order to fully characterize the compressor. In the first phase, the front block of the compressor is built and tested at corrected (referenced) air flow rate, inlet pressure, temperature and shaft rotational speed. Instrumentation includes utilizing traditional rakes and surveys at the exit, to obtain spanwise distributions of pressure, temperature, and flow angles. Testing in phases is typically done for two reasons. Read More

The History of Turbochargers, Part 2

Hello! And welcome back for part 2 of our series on “A Brief History of the Turbocharger”. To read part 1, which compares superchargers and turbochargers, and explains the early history of turbochargers and forced induction from the turn of the century through to World War 1, click here. Having covered all of that, let’s pick up from where we left off!

Following World War 1, and the work of Dr. Sanford Alexander Moss, Alfred Büchi, who had created the first true turbocharger, had continued innovating following the failure of his first design. By 1925, he had a working turbocharger design that consistently and reliably worked (1).

Following this breakthrough, the turbocharger saw its first commercial application on ten-cylinder diesel engines. Since diesel engines are typically built to withstand the high-pressures required by their operating conditions, the pressures generated by using forced induction are easily accommodated. As a result of adding the turbochargers, the engines upped their horsepower ratings from 1750HP, all the way to a whopping 2,500HP. (1)

The Hansestadt Danzig, one of the German ships fitted with the 10 cylinder turbodiesel engine described above
The Hansestadt Danzig, one of the German ships fitted with the 10 cylinder turbodiesel engine described above. (shipspotting.com)

For Büchi, this was a great achievement, as it marked the first commercial application of a machine that he had first begun working with more than 20 years prior. For the turbocharger, however, this was just the beginning. Read More

Anti-Icing Systems in Airplanes: Boeing 737-300/400/500

Through the decades, the aircraft industry always improved their onboard systems to get the best performances, security and comfort. In order to build a lasting travel type, security of the aircraft is one of the main goals for engineers. Due to rough exterior conditions while flying, especially at high altitude, with relative humidity and very low temperatures, the freezing temperature can cause the plane to ice. Ice can have major impacts on the aircraft’s weight and aerodynamical phenomena, – especially the lift – (the lift can decrease to 40% due to ice). Modeling and installing a specific system to prevent ice is a necessity. Therefore, aircraft designers developed an anti-icing system inside the wing to prevent ice.

There are several anti-icing systems on aircraft, mostly depending of the engine’s type. Most of aircrafts use the bleed air system, which consists of using a hot bleed air to warm up the wing leading edge. Another system named de-icing boots system is mostly used on turboprop aircrafts and consists of black rubbers at locations prone to icing which inflate and literally break the ice. Another system is simply an electrical leading edge warm up directly installed in the wing leading edge. Those examples are just an introduction to some anti-icing systems that aircraft industry has develop and are using. Each have pros and cons.

Here, we will focus on the anti-icing system using hot bleed air. This approach is used by the Boeing 737-300/400/500 anti-icing system with hot bleed air warming the leading edges.

Typically, this type of anti-icing system consists of a hot bleed air flow provided by the engine compressor’s stages to warm up the plane’s wing leading edge. The wing anti-icing system is made of two independent pneumatic systems among others, providing hot bleed air from each of the two turbofans separately. The hot bleed air is ducted via the engine bleed valve from the fifth compressor stage. If the pressure isn’t enough, bleed from the ninth compressor stage can additionally be used. Note that the fifth stage bleed air temperature is approximately 340°C and the ninth stage one is approximately 540°C which are too hot to be used in aircraft’s pneumatic systems such as hydraulic pressurization or potable water system pressurization for example. The hot air then runs through a pre-cooler to reduce the temperature to 200°C and this cooled air is distributed via the bleed ducts to consumers like the air conditioning packs for example and the wing anti-icing system. In order to know the moment to use the anti-icing system, the aircraft’s pilots use the visual ice indicator which is situated in the middle beam of the window. Once the probe is icing, the pilots enable the anti-icing system. Hence, hot bleed air is provided to the slates number three, four and five as shown in Figure 1.

Landing Edge Slats
Figure 1 – Leading Edge Slats

Due to the larger diameter and the aerodynamics phenomena, slates number one and two do not need any anti-icing devices. Once the anti-icing system is enabled, the hot bleed air is guided along telescopic pipes then is distributed via piccolo tubes as shown in Figure 2. From there, it exits the piccolo tubes through little holes, warms the wing leading edge and flows out of the wing through exit holes situating on the wing’s lower surface. Read More

A Brief History of the Turbocharger – Part 1

Turbochargers are one of the more common turbomachines out there today! As everyone is making efforts to lower carbon dioxide emissions in automobiles, and the automotive OEMs engage in a “horsepower war”, the turbocharger will likely continue to grow in popularity for both civil and commercial uses.

But how did these machines get so popular? That’s what we’ll be exploring in this blog miniseries! Today’s blog will introduce the concept of the turbocharger, and the beginnings of its development around the turn of the 20th century.

Turbocharging engines and the idea of forced induction on internal combustion engines are as old as the engines themselves. Their intertwined history can be traced back to the 1880’s, when Gottlieb Daimler was tinkering with the idea of forced induction on a “grandfather clock” engine. Daimler was supposedly the first to apply the principles of supercharging an engine in 1900, when he mounted a roots-style supercharger to a 4-stroke engine.

The birth of the turbocharger, however, would come 5 years later, when Swiss engineer Alfred Büchi received a patent for an axial compressor driven by an axial turbine on a common shaft with the piston of the engine. Although this design wasn’t feasible at the time due to a lack of viable materials, the idea was there.

Turbochargers vs Superchargers

What idea was that, exactly? And how did it differ from supercharging?

I think it’s important to quickly go over the basic differences between turbocharging and supercharging. Both offer “forced induction” for piston engines. A naturally aspirated engine simply will draw in atmospheric air as the intake valve opens, and the piston travels down to bottom dead center. A forced induction engine, pushes more air into the cylinder than what the dropping of the piston would pull in, allowing more air to be combusted, and thus generating more power and efficiency. While turbochargers and superchargers are both forced induction , how superchargers and turbochargers go about compressing that air is different. Superchargers are driven by the engine themselves, typically via a belt or gear. This uses some of the engine’s available horsepower, but doing so provides more horsepower back to the engine. The compressors can be either positive displacement configurations (such as a Roots or Twin-Screw), or a  centrifugal supercharger.

supercharger configurations
A very helpful image of the 3 kinds of superchargers, courtesy of MechanicalBooster.com

Turbochargers, as mentioned before, use the air from the exhaust of the engine to drive a turbine, and the work of the turbine is transmitted on a common shaft to a compressor. The most common configuration is a radial turbine driving a centrifugal compressor similar to the one above in the supercharger diagram. However, there are other configurations ,seen in larger examples, such as an axial turbine driving a centrifugal compressor. Read More

Aircraft Fuel Systems

The airplane is a complex technical object. Like a human or other organisms, it consists of numerous vital systems; with one of the more critical ones being the fuel system. It is important part of any vehicle, let alone aircraft, aside from  the newest electric powered vehicles.

An aircraft’s fuel system provides fuel that is loaded, stored, managed and transported to the propulsion system of the vehicle[1, 2]. As aviation fuel is liquid, this system can be considered as hydraulic. Therefore, it’s able to be mapped out and modeled for analysis in a program like AxSTREAM NET™.

The Typical Fuel System of a Narrow-body Passenger Plane

For an example of a conventional aviation fuel system, consider a typical narrow-body airliner with two engines. Some of the popular planes in this category include the Boeing 737, the Tupolev Tu-204, Airbus A320, Comac C919, Sukhoi Superjet 100, Bombardier CRJ, Embraer E-Jet and Mitsubishi Regional Jet[3].

The storage fuel system is shown in figure 1 is for the Boeing 737-300. The fuel is kept in an integral tank that is divided to five separate subdivisions. They are the central, wing (main) and surge tanks[4].

Storage fuel system of a Boeing 737
Figure 1 – Storage Fuel System of a Boeing 737-300 [4]
The hydraulic scheme of the Boeing 737’s fuel system is shown in Figure 2. For fueling and defueling the storage system there are ports on the starboard wing. The system does not have pumps to onboard fuel, so fuel is pumped into the plane via a fuel truck. The other critical part of the fuel system is the line which delivers fuel to the two engines and the auxiliary power unit. In this line there are two boost centrifugal pumps by each engine.
Read More

It’s Rocket Science – and it’s Dangerous!

Rockets have always fascinated us and to this day a rocket launch is still a global news event worth watching. The sheer noise, power and sight after you hear that “…3-2-1, Lift off!” leave us in awe. A masterpiece of engineering, the recent historic manned SpaceX Falcon 9 launch was no exception. Or was it?

The beginnings

From the outside, a rocket does not look especially advanced – a mere ‘stick’ with a big flame shooting out at one end. The principal concept is simple, too, but the inner workings of a modern liquid-fuel rocket are highly complex.

The first rockets are believed to have existed in China, around 1200. The invention of gunpowder was crucial to the development of these primitive rockets, which were fireworks initially and then weapons. Multistage so-called ‘fire arrows’ were documented during the early Ming Dynasty (Figure 1). The designs were based on bamboo sticks – still a little way off a Falcon 9.

Figure 1: The oldest known depiction of multistage rocket arrows, from 14th-century China. The top arrow reads ‘fire arrow’, the middle ‘dragon-shaped arrow frame’, and the bottom’complete fire arrow’. Source

With the rise of gunpowder, this crude rocket technology spread throughout the Middle East and Europe.

The next rocketry milestone came in the 1780s, when the Indian military developed Mysorean rockets with iron castings and successfully deployed them against the British East India Company. Read More

Engineering Luke Skywalker’s X-34 Landspeeder

Today, landspeeders we look at!

Introduction

Landspeeders belong to the “repulsorlift” transport class, like the podracers we looked at last year, and travel above a world’s surface (up to 2 meters) without contact (very useful on swampy lands like Dagobah). Landspeeders are the successors to the hanno speeder which was mainly used as a racing vehicle with many Tatooine natives still using them to race in the Boona Eve Classic today.

Luke Skywalkers Soro Suub Corporation X-34 landspeeder
Figure 1:  Luke Skywalker’s Soro Suub Corporation X-34 landspeeder from the 1977 film – Note, the Soro Suub Corporation was your main go-to landspeeder designer and manufacturer before and during the reign of the Galactic Empire even though it specialized mostly in mineral processing. Image source

Landspeeders are found in both civilian and military applications but due to intergalactic ITAR regulations we will only cover the civil aspect here with a focus on the most famous of them all. If you want to know more about our experience working with military, defense and governmental organizations (whether you area part of the Empire, Rebels, Resistance or Separatists) feel free to contact us.

The Famous X-34

Luke Skywalker’s X-34, with its 6 selectable hover heights, features an engine consisting of 3 air-cooled thrust gas turbines able to reach a top speed of about 155 mph. The side engines are also used for steering although it is not obvious whether this steering is achieved by varying their thrust to be asymmetric or through vectoring of their exhaust. With the X-34 total length being 3.4 meters it helps us estimate the overall dimensions of its engines which are, each, roughly 80 cm long by 30 cm wide. Read More