#### Turbomachinery CFD Simulation: Art in Motion

This is an excerpt from the Siemens Blog. You can read the full version here.

Originally Written By Justin Hodges - July 14, 2020

Believe it or not, there is some true art in turbomachinery CFD simulation. From the creamer in your coffee to the tumbling of flow through a small waterway. There is something palpable with intrigue when observing fluid flows in our everyday routines. As computational fluid dynamics practitioners, we are fortunate to have a unique opportunity. That is to simulate and observe these same curious fundamentals of turbulence and fluid flow until our heart is content.

#### Vertical Pumps: What Are They, Where Are They Used and How To Design Them?

Introduction

Vertical pump designs are similar to conventional pumps, with some unique differences in their applications.  Pumps use centrifugal force to convert mechanical energy into kinetic energy and increase the pressure of the liquid. Vertical pumps move liquids in the vertical direction upwards through a pipe. All pumps pressurize liquids, which are mostly incompressible. Unlike compressible gases, it is impossible to compress liquids, therefore the volumetric flow rate can not be reduced. Therefore liquids are transported by pumping and the inlet volume flow rate is equal to the exit volume flow rate.

Vertical centrifugal pumps are simply designed machines, and have similarities to their horizontal counterparts. A casing called a volute contains an impeller mounted perpendicularly on an upright (vertical) rotating shaft. The electric drive motor uses its mechanical energy to turn the pump impeller with blades, and imparts kinetic energy to the liquid as it begins to rotate. These pumps can be single stage or multistage with several in-line stages mounted in series.

The centrifugal force through the impeller rotor causes the liquid and any particulates within the liquid to move radially outward, away from the impeller center of rotation at high tangential velocity. The swirling flow at the exit of the impeller is then channeled into a diffusion system which can be a volute or collector, which diffuses the high velocity flow and converts the velocity into high pressure. In vertical pumps, the high exit pressure enables the liquid to be pumped to high vertical locations. Thus the pump exit pressure force is utilized to lift the liquid to high levels, and usually at high residual pressure even at the pipe discharge.

Applications of Vertical Pumps

An “in line” vertical pump is illustrated in Figure 1 (Reference 1), where the flow enters horizontally and exits horizontally and can be mounted such that the center line of the inlet and discharge pipes are in line with each other.  This is a centrifugal pump with a tangential scroll at the inlet that redirects the flow by 90 degrees and distributes it circumferentially and in the axial direction into the impeller eye. The discharge is a simple volute that collects the tangential flow from the impeller exit, and redirects it into the radial direction.

Figure 2 shows a vertical pump that has a vertical intake that directs the flow straight into the eye of the pump rotor. At the impeller exit, the tangential flow is collected by a volute and diffused in an exit cone. An elbow after the exit cone redirects the flow into the vertical direction to lift the liquid to the desired altitude. (Reference 2). Read More

#### Back to Basics: What Makes a Good Pump?

Update – February 28, 2023: AxCYCLE is our legacy software and is depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

Everyone is familiar with pumps, but how many people really think about how much depends on this ubiquitous invention? The scope of pump applications is wide: distribution and circulation of water in water supply and heat supply systems, irrigation in agriculture, in the oil industry, in fire extinguishing systems, etc.

A pump is a hydraulic machine designed to move fluid and impart energy to it. A schematic diagram of a simple pumping unit is presented below.

Positive Displacement and Dynamic Pumps

According to the principle of operation, pumps can be divided into two main groups: positive displacement and dynamic. In positive displacement pumps, a certain volume of the pumped liquid is cut off and moved from the inlet to the pressure head, where additional energy is supplied to it. In pumps with dynamic action, the increase in energy occurs due to the interaction of the liquid with a rotating working body.

The most widely used pumps are centrifugal pumps which are of the dynamic type. The principle of centrifugal pumps uses a rotating impeller to create a vacuum in order to move the fluid. The impeller rotates within the housing and reduces pressure at the inlet. This motion then drives fluid to the outside of the pump’s housing, which increases the pressure.

These pumps benefit from a simple design and lower maintenance requirements and costs. This makes them suited to applications where the pump is used often or continuously run.

In most cases, the pumps are electrically driven, but if the pump is of high power and high speed, then these pumps are driven by steam turbines. Read More

#### Pump Rotor Dynamics – from Residential Pools and Human Hearts to Heavy Duty Industry Applications

You rarely find a rotary machine with a wider range of applications than pumps. These machines acting in a single role can be installed both to supply the water to a garden pool and move the crude oil in pipelines.

And even more, the same simple pump can substitute the functions of the human heart by moving the blood through it.

Although the heavy duty industry applications of pumps are less delicate at first sight, they can still generate similar effects of this unique nature which is inherent only to this type of machine and should be studied carefully when executing rotor dynamics calculations. Read More

#### The Lovable Underdog of Turbomachinery

Everyone knows that APUs need love too…..

For Valentine’s Day, we want to look at an underdog of turbomachinery. A machine that is often overlooked, and not really in the limelight the way some of its larger cousins are, nor is it given the trendy position of being the “technology of the future” like its smaller cousins. Without this technology, airplanes would be entirely reliant on external power plants to maintain an electric power supply on the ground, and to start the main engines. So, what is this underappreciated machine?

If you haven’t been able to guess it, our Valentine this year is the aircraft auxiliary power unit, or APU for short. Although these are not present on all aircraft, they are typically used in larger airplanes such as commercial airliners. This allows aircraft to rely less on ground services when the main engines are not running. As a result, less equipment, manpower, and time are required to keep the plane in standby mode, and the aircraft can also service airports with less available resources in remote locations.

Where this Underdog Started

The aircraft auxiliary power unit can be traced back to the First World War, as they were used to provide electric power onboard airships and zeppelins. In the Second World War, American bombers and cargo aircraft had these systems as well. APUs were small piston engines, as the gas turbine had yet to be developed. These engines were typically V-twin or flat configuration engines, similar to what you might find on a motorcycle, and they were called putt-putts. These two-stroke engines usually put out less than 10-horsepower, but that was all that was required to provide DC power during low-level flight.

#### Aircraft Fuel Systems

Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

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].

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.

#### Centrifugal Compressor Reverse Engineering and Digital Twin Development

Centrifugal Compressors are the turbomachines also known as turbo-compressors, and belong to the roto-dynamic class of compressors. In these compressors the required pressure rise takes place due to the continuous conversion of angular momentum imparted to the working fluid by a high-speed impeller into pressure. These compressors are used in small gas-turbines, turbochargers, chiller units, in the process and paper industries, oil & gas industries and others.

The design and manufacturing of such compressors are always challenging because of its 3-dimensional shapes, high rotational speeds that interact with different loss mechanisms, and stringent working environments. In many circumstances, it is necessary to analyze an existing compressor, with the end goal being to redesign it, enhance its performance, or to use it in completely different applications. In order to meet such requirements, reverse engineering is a viable option. With reverse engineering, one can review competitor’s design to remain in market competition.

Reverse Engineering

Reverse engineering allows us to collect incomplete or non-existing design data and manufacture an accurate recreation, safely, of the original product or component.

Sometimes, it is also referred to as back engineering, in which centrifugal compressors or any other product are deconstructed to extract design information from them. Oftentimes, reverse engineering involves deconstructing individual components like the impeller or diffuser of larger compressors. End-users often use this approach when purchasing a replacement impeller or any other compressor part from an OEM is not an option. In some cases, where older impellers that have not been manufactured for 20 years or more, the original 2D drawings are no longer available.  When this is the case, the only way to obtain the design of an original compressor is through reverse engineering.

Reverse engineering requires a series of steps to gather precise information on a product’s dimensions. Once collected, the data can be stored in digital archives. Figure 1 (left) shows the typical process of reverse engineering. In figure 1 (right), one can see the scanning process of the centrifugal impeller using a laser scanner.

To reverse engineer an impeller or any other part of compressor, an organization will typically acquire the component and take it apart to examine its internal mechanisms. This way, engineers can unveil information about the original design and construction of the product. One can start by analyzing the dimensions and attributes of the impeller and make measurements of the blade widths, diameters and angles, as these dimensions often relate to the compressor’s performance. Read More

#### Hans von Ohain – The Other Father of Jet Engines and the Gas Turbine

The question of who invented the jet engine is often met with two different answers, and neither is really wrong. In fact, we posed this question on our LinkedIn page, and got the same mixed results seen elsewhere.  Both Sir Frank Whittle and Hans von Ohain were responsible for inventing the turbojet engine at the same time. While Dr. von Ohain knew of Sir Frank’s work, he did not draw information from, while Sir Frank was unaware that anyone else was designing a turbojet engine.  While we’ve covered Sir Frank Whittle before, today we’ll be looking at the life of Hans von Ohain, his invention of the turbojet, and his contributions to turbomachinery engineering.

Dr. Hans Joachim Pabst von Ohain was born on December 14, 1911 in Dessau, Germany. He went to school at the University of Göttingen where he received his PhD in Physics and Aerodynamics in 1935. During his studies and following his graduation, he was captivated by  aviation and airplane propulsion, with a specific interest in developing an aircraft that did not rely on a piston-driven propeller. According to the National Aviation Hall of Fame, he “conceived the idea for jet propulsion in 1933 when he realized that the great noise and vibrations of the propeller piston engines seemed to destroy the smoothness and steadiness of flying”. (1) Read More

#### Modern Challenges in Aviation Propulsion Systems

Update – February 28, 2023: AxCYCLE is our legacy software and is depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

Introduction

Aviation is coming into a new age of carbon free energy, similar to what is being explored with ground transportation. Currently, aviation transportation generates about 2.5% of the global CO2 emission [1]. Several countries have introduced targets to achieve net-zero emissions by 2050 [2].

Many aerospace teams have joined the great engineering challenge to change the future of aviation.  With this, a number of different types of aircraft with different types of propulsion systems have been proposed.

Hybrid Propulsion System

The first step to a carbon-free propulsion system is hybrid technology. This kind of power plant increases efficiency, decreases emission of greenhouse gases and uses a traditional engine to produce electricity and electric motors to drive the fans or propellers [3].

The chemical engines operate at optimal conditions at any mode of a route. On the other hand, the electric motor is able to work in generator mode, using the kinetic energy of the vehicle during deceleration.

The hybrid aircraft is classified by several attributes. Using thrust devices, we will consider the two base types of propellers and fans. Read More

#### 2020 – The Most Challenging Year in Recent Memory Comes to a Close Pt. 2

Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.

##### Turbomachinery, Humanized

The SoftInWay turbomachinery blog is known for its technical breakdowns and explanations of mechanical engineering theory and practices, as well as introductions to things like rotor dynamics. This year however, the marketing team also wanted to cover some of the individuals behind the advances in turbomachinery and engineering by looking at figures like Sir Frank Whittle and Sir Charles Parsons among others.

We looked at the big picture, and why the developments of the steam and gas turbines were so crucial to mankind. In addition to the revolutionary changes in global transportation brought about by jet engines and steam turbines, we also examined the turbocharger, which has become a game changer in the automotive industry as automakers are locked in a race to improve engine performance and fuel economy while reducing greenhouse gas emissions. After all, why learn the theories of mechanical engineering if not to make advances in science, technology, and society overall? Read More