Integrated Design and Analysis of Turbofan Engines

[:en]High bypass ratio (BPR) fans are of heightened interest in the area of civil air vehicle propulsion. It increases the air inhaling and improves both the thrust and the propulsive efficiency. The specific fuel consumption is also reduced in today’s turbofan engines.

The inlet fan designs and optimizations are very important as the fan can be subjected to different inlet conditions. As a matter of fact, a modern high bypass fan system provides over 85% of the engine’s net thrust. Hence, a well-designed bypass fan system is crucial for the overall propulsion characteristics of a turbofan engine. A tool which can perform both inverse tasks and direct tasks on bypass fan system is a necessity for turbofan design.

Figure 1 - Turbofan
Figure 1 Meridional Section of the Turbofan Engine
AxSTREAM ® Streamline Solver

The AxSTREAM® streamline solver is a throughflow solver, the specificity of the outcome one should expect from this solver is up the meridional flow field. Hence, when we develop the model, we shall take Acarer and Özkol’s work [2016] as a reference example. Read More

Oil Systems for Turbine Lubrication

[:en]The oil system is an integral element of the turbine unit, which largely determines its reliability and trouble-free operation. The main purpose of the turbine lubricating oil system is to provide fluid friction in the bearings of turbines, generators, feed pumps, and gearboxes.

An oil system should provide:

– continuous supply of the required amount of oil in all modes of operation of the turbine unit, which guarantees:

  • – prevention of wear on friction surfaces;
  • – reduction of friction power losses;
  • – removal of heat released during friction and transmitted from the hot parts of the turbine

– maintaining the required temperature of the oil in the system; and

– cleaning the oil from contamination.

At the same time, the necessary qualities of the lubricating oil system are reliability, safety of operation, ease of maintenance.

The pressure and the temperature of the oil should be constantly monitored during operation of the turbine unit. Specifically, the lube oil temperature after the bearings requires special attention. Overheating of the bearing leads to wear of the working parts and changes in the properties of the lubricant itself. The quality of the lube oil is controlled by physicochemical characteristics such as density and viscosity. The system leaks must be stopped quickly and oil replenished on time. These factors will significantly extend the service life of the steam turbine.

Nowadays, computer simulation is a very powerful and useful tool. It helps you predict the processes occurring in the bearing chambers, and determine the flow of the working fluid when the operating modes change, all without installing expensive experimental equipment.

We suggest using the 1D-Analysis AxSTREAM NET™ tool to simulate the lubrication system. This software product allows you to quite simply, clearly and quickly build the desired model. It provides a flexible method to represent fluid path as a set of 1D elements, which easily can be connected to each other to form a thermal-fluid network. The program calculates fluid flow parameters for inlet and outlet of each element. There are many different components that allow you to simulate stationary and non-stationary modes. Also there is a convenient library of fluids. It is also possible for a user to add fluids of their choice.

The example of modeling in AxSTREAM NET™ is the system of oil supply for the K-500-240 turbine. This turbine is quite massive with bearing loads of up to 450 kN. The schematic diagram of the oil supply K-500-240-2 is shown in Figure 1.

Figure 1 Principle Scheme of K-500-240 Steam Turbine
Figure 1. Principle Scheme of K-500-240 Steam Turbine.

 

(1 – main tank; 2 & 3 – pumps; 4 – oil cooler; 5 – damp tank; 6 – journal bearings; 7 – thrust bearing).

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An Overview of Axial Fans

[:en]Axial fans have become indispensable in everyday applications starting from ceiling fans to industrial applications and aerospace fans.  The fan has become a part of every application where ventilation and cooling is required, like in a condenser, radiator, electronics etc., and they are available in the wide range of sizes from few millimeters to several meters. Fans generate pressure to move air/gases against the resistance caused by ducts, dampers, or other components in a fan system. Axial-flow fans are better suited for low-resistance, high-flow applications and can have widely varied operating characteristics depending on blade width and shape, number of blades, and tip speed.

Fan Types

The major types of axial flow fans are: propeller, tube axial, and vane axial.

  • – Propellers usually run at low speeds and handle large volumes of gas at low pressure. Often used as exhaust fans these have an efficiency of around 50% or less.
  • – Tube-axial fans turn faster than propeller fans, enabling operation under high-pressures 2500 – 4000 Pa with an efficiency of up to 65%.
  • – Vane-axial fans have guide vanes that improve the efficiency and operate at pressures up to 5000 Pa. Efficiency is up to 85%.
Types of Fans
Figure 1 Different Types of Axial Fans
Aerodynamic Design of an Axial Fan

The aerodynamic design of an axial fan depends on its applications. For example, axial fans for industrial cooling applications operate at low speeds and require simple profile shapes. When it comes to aircraft applications however, the fan must operate at very high speeds, and the aerodynamic design requirements become significantly different from more traditional fan designs. Read More

Redesigning Anakin Skywalker’s Podracer

[:en]Ever since circa 100 BBY, Podracing in its modern version has drawn crowds from far far away to watch pilots compete in races like the Boonta Eve Classic which made Anakin Skywalker famous and won him his freedom. By beating Sebulba, the Dug, and the other Podracers, Anakin became the first human to be successful at this very dangerous sport. The Force helped him in his victory by sharpening his reflexes, but his repulsorcraft was also superior due to its size and the modifications made to its twin Radon-Ulzer 620C engines, especially the fuel atomizer and distribution system with its multiple igniters which makes them run similarly to afterburners seen on some military planes on Earth.

Figure 1 Pilots and their Repulsorcrafts at the Start of the Boonta Even Classic Race on Tatooine
Figure 1 Pilots and their Repulsorcrafts at the Start of the Boonta Eve Classic Race on Tatooine

Let’s take a deeper look at what repulsorcrafts are and how we can help Anakin redesign his to gain an even better advantage against the competition, provided that Watto has the correct equipment in his junk yard. Read More

Complex Modeling of a Waste Heat Boiler

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Introduction

Waste heat boilers are a sophisticated piece of equipment important for recovering heat and in turn protecting the environment. Waste heat boilers are needed during the operation of facilities in the energy sector such as gas turbine plants and diesel engines, as well as in metallurgy and other industries where excessive heat of high temperature up to 1,000 degrees form during the technological processes. Waste heat boilers are used to recover excess heat energy, as well as to increase the overall efficiency of the cycle. Another feature of waste-heat boilers used at these installations is to protect the environment – by disposing of harmful emissions.

This article discusses the accurate modeling of these sophisticated waste heat boilers. We will consider the simulation of a Heat Recovery Steam Generator (HRSG), which is used in a combined steam-gas cycle for utilizing the outgoing heat from a gas turbine plant and generating superheated steam, using the programs thermal-fluid network approach and complexes of optimization.

The HRSG has four main heat exchangers: cast-iron economizer, boiling type steel economizer, evaporator with separator, and superheater.

On the one side of the HRSG, feed water is supplied from the cycle, and on another side, hot gas is supplied from the gas turbine in the process of operation.  The water is preheated and goes to the steel economizer where the boiling process begins in the tubes. After the process in the economizers, the water goes to the shell side of the evaporator, where its active boiling occurs. In the separator, the steam-water mixture is divided into saturated steam and overflow. Saturated steam is sent to the superheater, where superheated steam is formed and goes to the steam turbine cylinder. Overflow water returns to the steam formation. An induced-draft fan is used for gas circulation and removal in the HRSG. The HRSG model also has a spray attemperator for steam cooling. The operation principle of desuperheater is the following: feed water is taken from the economizer and goes to the superheater section, passes to superheated steam flow through nozzles, finely divided water droplets mix, heat up and evaporate and as a result, the steam is cooled.

HRSG Flows Direction
Picture 1 – HRSG Flows Direction
Different Approaches

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Aircraft Fuel Pump Design and Optimization

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Introduction to Aircraft Fuel Pumps

Aircraft fuel pumps are one of the most important elements of a fuel system. The operating characteristics and reliability of it are critical for the performance and safety of the aircraft.

Usually, the inlet pressure of the aircraft fuel pump is very low, for example, the aircraft fuel pump of a commercial aircraft needs to operate at altitudes up to 45,000 feet, where the standard atmospheric pressure is about 2.14 psi (about 0.146 atm). What’s more, because fuel is the only consumable fluid carried by the aircraft, it needs to provide all of the cooling necessary for the proper function of the airframe and engine systems. As a result, the temperature of the fuel in the pump increases significantly. The vapor pressure of common fuel used in aircraft gas turbine engines, like Jet A, Jet B, JP-4 etc., gets higher as the temperature increases. Cavitation may occur when the local static pressure in the fluid drops below the vapor pressure of the fuel.

It is very important to avoid the cavitation problem when designing the aircraft fuel pump, because it will cause serious wear, tear, damage of the impeller and performance penalty, which reduces the pumps’ lifetime dramatically. In order to prevent cavitation and have a better suction performance, aircraft fuel pumps use inducers either alone or in conjunction with radial or mixed-flow impeller depending upon the flow and pressure requirements. Figure 1 shows an assortment of fuel pump impellers including radial, mixed flow and inducer types. [1]

Fuel Pump Impeller
Fig.1 Various Fuel Pump Impellers
Designing an Aircraft Fuel Pump with AxSTREAM®

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To Retrofit or Not to Retrofit – 7 Questions to Help you Decide

[:en]One of the challenges of maintaining infrastructure is deciding how best to keep the operational costs in check while delivering the highest amount of service. This is especially true for aging equipment. One option is to replace the equipment with a newer version entirely, continue to maintain the existing machine, or a third option, retrofit the current machine with updated features.

Retrofitting is a term used in the manufacturing industry to describe how new or updated parts are fitted to old or outdated assemblies to improve function, efficiency or additional features unavailable in the earlier versions.

steam turbine in repair process, machinery, pipes, tubes, at power plant
steam turbine in repair process, machinery, pipes, tubes, at a power plant

Retrofitting, like any investment of capital requires careful thought.  SoftInWay’s Manage ring Director, Abdul Nassar has put together a simple list of questions to ask yourself before committing to a retrofit project.  Answering these seven questions before you start can save you considerable time and effort. Read More

A Basic Guide to Reverse Engineering

[:en]Reverse Engineering, or back engineering, is a term used for the process of examining an object to see how it works in order to duplicate or enhance the object when you don’t have the original drawings/models or manufacturing information about an object.

There are two major reasons reverse engineering is used:

  1.  create replacement parts to maintain the function of older machines;
  2.  improve the function of existing machines while meeting all existing constraints.

 

Figure 1 Uses of Reverse Engineering
Figure 1: Uses of Reverse Engineering

Reverse engineering is extremely important in turbomachinery for replacement parts in turbines or compressors which have been operating for many years. Documentation, reports and drawings for a significant amount of these machines is not available due to a variety of reasons, therefore keeping these important machines running is a challenge. One of the options to deal with this issue is to buy the modern analogue of the machine, which is not always feasible due to economic constraints or that there is no replacement available.  Reverse engineering of the worn out parts might be the best option in the majority of cases.

In any case, the process to recovery original geometry of the object is the first and major step for all reverse engineering projects, whether you want just replacing/replicate parts or proceed with an upgrade to the machine.

Basic Steps to Any Reverse Engineering Project

Any reverse engineering process consist of the following phases:

  1. Data collection: The object needs to be taken apart and studied.  Starting in ancient times, items were disassembles and careful hand measurements were taken to replicate items.  Today, we employ advanced laser scanning tool and 3D modeling techniques to record the required information in addition to any existing documentation, drawings or reports which exists.
  2. Data processing: Once you have the data, it needs to be converted to useful information.  Computers are essential for this stage as it can involve the processing of billions of coordinates of data converting this information into 2D drawings or 3D models by utilizing CAD systems.
  3. Data modeling: This step was not available in beginning of reverse engineering. People just tried to replicate and manufacture a similar object based on the available data. Nowadays, engineers can utilize digital modelling, which represents all details of the geometrical and operational conditions of the object through a range of operation regimes. Typically, performance analysis and structural evaluation are done at this stage, by utilizing thermo/aerodynamic analytical tool, including 3D CFD and FEA approaches.
  4. Improvement/redesign of the object: If required, this is the step where innovations can be created to improve the effectiveness of the object based on the collected data about the object’s geometry and operation.
  5. Manufacturing: After the part is been modeled and meets the design requirements, the object can be manufactured to replace a worn out part, or to provide increased functionality.
Reverse Engineering in Today’s World

It very common to find the situations where reverse engineering is necessary for parts replacement, particularly with turbomachinery – steam or gas turbines, compressors and pumps. Many of these machines have been in operation for many years and experienced damaging effects of use over that time – like water droplets and solid particles erosion, corrosion, foreign objects, and unexpected operating conditions. Besides these expected needed repairs, some other reasons for reverse engineering might arise from a components part failure, as well as part alterations needed due to previous overhauls and re-rates.

All the conditions mentioned above require not only recovering the original geometry but also an understanding of the unit’s history, material properties and current operating conditions.

This article focuses on reverse engineering objects which have experienced significant change in their geometry due to the challenges of long term operation and their shape could not be directly recovered by traditional methods – like direct measurement or laser scanning.  Pictures below are examples of such objects – steam turbines blading with significant damage of the airfoils with different causes such as mechanical, water/solid particle erosion, and deposit.

Figure 2 Water droplet erosion on steam turbines long blades
Figure 2: Water droplet erosion on steam turbines long blades
Figure 3 Steam turbine blading with mechanical damage
Figure 3: Steam turbine blading with mechanical damage
Figure 4 Steam turbine control stage nozzles solid particle erosion
Figure 4 Steam turbine control stage nozzles solid particle erosion
Figure 5 Deposits on Rotating Blades
Figure 5: Deposits on Rotating Blades

In the situations shown above, recovering the original geometry may be impossible if an engineer only has the undamaged portion of original part to work with. Which means that relying on undamaged portion of an original part it may be impossible to recover the needed portion due to significant level of damage.

Looking at the eroded turbine blading in Figure 1, recovering these airfoils with sufficient accuracy based on only a scan of the original part, would be very difficult, if not impossible, considering that 1/3 to ½ of the needed profile is wiped out by erosion.

In order to recover the full airfoil shape for turbines / compressors / or pumps blading, the information about flow conditions – angles, velocities, pressure, temperature – is required to recreate the airfoils profiles and a complete 3D blade.

In many cases with significant blading damage, the information obtained from aero/thermodynamic analysis is the only source of the information available for a designer and the only possible way to recover turbomachinery blading. In fact, in such a situation, the new variant of the airfoils is developed based on aero/thermodynamic information and by considering the remaining portion of the part, which would be the most accurate representation of the original variant. A structural evaluation should also be performed for any recovered part to ensure blading structural reliability in addition to the aero/thermodynamic study.

All of these engineering steps require employment of dedicated engineering design and analysis tools, which can perform:

  • – Accurate modelling of the turbo machinery flow path,
  • – 1D/2D aero/thermodynamic analysis and in some cases 3D CFD,
  • – Profiling and 3D staking of the blading,
  • – Structural evaluation, including 3D FEA tools.

SoftInWay’s team offers a comprehensive set of turbomachinery design and analysis tools within the integrated AxSTREAM® platform, which covers many steps, required for reverse engineering activities.

In Figure 6 below, a process diagram shows how AxSTREAM® products are used for reverse engineering.

Process Diagram
Figure 6: Process diagram of AxSTREAM® products use in reverse engineering

After data collection, most of the geometry recovering steps are processed by AxSTREAM® modules:

  • AxSLICE™ to process original geometry data, available from the scanned cloud of points.
  • AxSTREAM® solver to perform 1D/2D aero/thermodynamic
  • AxSTREAM® profiler to recover profile shape and 3D airfoil stacking.
  • AxSTRESS™ for structural evaluation and 3D design.
  • AxCFD™ for detailed aerodynamic analysis and performance evaluation.

Geometry recovered in this way is now ready to be used to develop detailed 3D CAD models and 2D drawings for further technological and/or manufacturing processing.

As an example of such capabilities, Figure 7 demonstrates the reverse engineering process for the 1000 mm last stage of 200 MW steam turbine with significantly damaged blades due to water erosion.

It is possible to recognize and extract the profile angles with a specialized tool – AxSLICE™, obtain slices on the desired number of sections and insert the extracted geometric data to an AxSTREAM® project.

200 MW steam turbine water eroded 1000mm last stage blade reverse engineering process using AxSTREAM and upgraded variant of the blade
Figure 7: 200 MW steam turbine water eroded 1000mm last stage blade reverse engineering process using AxSTREAM® and upgraded variant of the blade.

The AxSTREAM® platform can provide seamless reverse engineering process for all components of complex turbomachinery.

Meet an Expert! 

Boris Frolov Dr. Boris Frolov has over 35 years of experience in steam/gas turbines design, analysis and testing. Earning his PhD in turbine stages optimization with controlled reaction, he is an expert in steam turbines aerodynamics and long buckets aeromechanics. Dr. Frolov has over 50 publications and 7 registered patents and he shares this vast knowledge as a lecturer in steam turbines, gas dynamics and thermodynamics for students studying power engineering sciences. [:]

An Introduction to Bearing Instability

Hydrodynamic bearings operating at high speeds encounter instability problems of oil whirl and whip. Instability may ruin not only the bearings but the entire machine. It is well-known that hydrodynamics bearings play an important role in determining and controlling the vibrations of a rotating machinery, because of the springs and dampers, and bearings strongly influence the critical speed and imbalance response. Under certain conditions, the bearings can create rotor instability which results in significant self-excited vibrations.

The types of stability here are for a balanced journal and are mentioned below. If, as time increases, the trajectory of the journal center goes to a point of the clearance circle and remains there indefinitely, then the bearing is considered to exhibit "point stability," Fig. 1(a). If, as time increases, the trajectory does not go to a point, as shown in Fig. 1(b) and (c), then the bearing, is considered to exhibit "point instability". Two types of instability are shown in Figure 1. In Fig 1(b) the trajectory continues to increases without bound, ultimately reaching the limit of the clearance circle, therefore, this case is called "unbounded ". As time increases eases, if the trajectory closes on itself forming a limit cycle, as shown in Fig 1(c), then the trajectory can be said to be "orbitally stable".

Types of Stability
Figure. 1 Types of stability

Satisfactory dynamic characteristics are essential to good bearing design. Hence it is very important for the designers to predict the journal center motion trajectories. AxSTREAM Bearing™ is used to calculate the hydrodynamic characteristics based on the mass-conserving mathematical model by applying the finite difference method with the successive over-relaxation (SOR) algorithm.

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[:en]Study of a Supercritical CO2 Power Cycle Application in a Cogeneration Power Plant[:cn]Evaluation for Scalability of a Combined Cycle Using Gas and Bottoming sCO2 Turbines[:]

[:en]This is an excerpt from a technical paper, presented at the ASME Power & Energy Conference in Pittsburg, Pennsylvania USA and  written by Oleksii Rudenko, Leonid Moroz, and  Maksym Burlaka.  Follow the link at the end of the post to read the full study! 

Introduction

Supercritical CO2 operating in a closed-loop recompression Brayton cycle has the potential of equivalent or higher cycle efficiency versus supercritical or superheated steam cycles at similar temperatures [2]. The current applications of the supercritical CO2 Brayton cycle are intended for the electricity production only and the questions which are related to the building of CHP plants based on Supercritical CO2 technology were not considered yet.

CHP is the concurrent production of electricity or mechanical power and useful thermal energy (heating and/or cooling) from a single source of energy. CHP is a type of distributed generation, which, unlike central station generation, is located at located at or near the point of consumption. Instead of purchasing electricity from a local utility and then burning fuel in a furnace or boiler to produce thermal energy, consumers use CHP to improve efficiency and reduce greenhouse gas (GHG) emissions. For optimal efficiency, CHP systems typically are designed and sized to meet the users’ thermal base load demand. CHP is not a single technology but a suite of technologies that can use a variety of fuels to generate electricity or power at the point of use, allowing the heat that would normally be lost in the power generation process to be recovered to provide needed heating and/or cooling. This allows for much greater improvement in overall fuel efficiency, therefore resulting in lower costs and CO2 emissions. CHP’s potential for energy saving is vast.

It should be noted that CHP may not be widely recognized outside industrial, commercial, institutional, and utility circles, but it has quietly been providing highly efficient electricity and process heat to some of the most vital industries, largest employers, urban centers, and campuses. While the traditional method of separately producing useful heat and power has a typical combined efficiency of 45 %, CHP systems can operate at efficiency levels as high as 80 % (Figure 1) [1].

Figure 1 - CHP Process Flow Diagram
Figure 1. CHP Process Flow Diagram.

Taking into consideration the high efficiency of fuel energy utilization of CHP plants and the high potential of the supercritical CO2 technology, the latter should be also considered as the base of future CHP plants. The comparison with traditional Steam based CHP plants also should be performed.

The study of CHP plant concepts were performed with the use of the heat balance calculation tool AxCYCLE™ [3].

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