#### Steam Turbine Seal Leakage Calculation in Design

Steam turbine seals are parts inserted between moving and stationary components, to reduce and prevent steam leakage and air leaking into the low pressure areas. The leakage can happen through vane, gland, and shaft, etc. To reduce leakage from those parts while guaranteeing smooth operation of a steam turbine, engineers have to design these seals, taking into account not only efficiency, but also mechanical strength, vibration and cost.

As an example, steam turbine flow path seals improve overall efficiency installing various types of shrouds, diaphragms, and end seals which prevent idle leaks of working steam in the cylinders. In steam turbines, labyrinth seals are widely used. Some labyrinth seals are also used with honeycomb inserts. It is believed that the use of such seals makes it possible to achieve a certain gain due to smaller leaks of working fluid and more reliable operation of the system under the conditions in which the rotor’s rotating parts may rub against the stator elements. However, we can only consider it as a successful design if the structures are compliant with the manufacturing capabilities and have good vibration stability. [1] Furthermore, seal leakage can significantly affect efficiencies. Better seals increase efficiencies but add extra cost to both manufacturing and maintenance, so the design needs to be done with the turbine flow path design. Although modeling the seals in 3D CFD is theoretically possible, the calculation resources and time are extremely demanding.

This important task can be completed very easily with AxSTREAM NETTM. AxSTREAM NETTM provides a flexible method to represent fluid path and solid structure as a set of 1D elements, which can be connected to each other to form a thermal-fluid network. For each fluid path section, the program calculates fluid flow parameters for inlet and outlet cross-sections, like velocity, density, temperature, mass flow rate, etc. Therefore, the leakage from the whole system can be modeled in this network, as shown in Figure 1.

AxSTREAM NET™ is capable of doing:

1. Choice of seal design at the stage of the steam/gas turbine preliminary design.
2. Calculation of balances of pressures and mass flow rate to correctly account for the efficiency of the steam/gas turbine.
3. Calculation of seals fluid flow parameters on the startup mode to estimate the thermal expansion of rotor and casing element.
4. Calculation of thermal boundary conditions for thermo stresses estimation.

#### Steam Turbine Aerodynamic Improvements for Significant Efficiency Gains

The steam turbine is one of the most important power generating equipment items in use. Around half of the electricity generated worldwide comes from steam turbines. Steam turbines can be fueled by coal, nuclear energy, petroleum or natural gas, alternatively by biomass, solar energy or geothermal energy. Thus a large amount of fuel can be saved and CO2 emissions significantly reduced by optimizing key components of these widely used machines.

An important goal in steam turbine technology is to improve efficiency. The continuous flow of steam conditions is one of the commonly accepted efficiency contributor for steam power plants. The chart below shows expected improvement in thermal efficiency for USC double-reheat fossil-fuel power units compared to common supercritical-pressure ones, according to Hitachi.

Besides steam condition elevation, other areas help the development and refinement of innovative aerodynamic flow path design approaches and the improvement of design procedures for nozzle and blades design and analysis. Continuous growth of steam conditions since the mid-1990s and some advanced steam path design for large steam turbines have brought about 5% of efficiency gain. This effect is almost the same as the transition from subcritical-pressure steam conditions to the supercritical-pressure ones with elevated steam temperatures illustrated in the figure above. Here are some practical examples of steam turbines high efficiency, achieved during the last decade by advanced aerodynamic design (source: Leizerovich, A. Sh. Steam turbines for modern fossil-fuel power plants, ©2008 by The Fairmont Press).

#### 1.1 Mathematical Models and the Object Design Problem

The methodology of a turbine optimal design as a complex multi-level engineering system should support the operation with diverse mathematical models, providing for each design problem communication between the neighboring subsystems levels.

One approach to turbine design with using of block-hierarchical representation consists in the transition from the original mathematical models for the subsystems and numerical methods of optimization to “all-purpose” mathematical model and general method of parameters optimization.

We will specify as original the mathematical model (OMM), which is a closed system of equations that describe the phenomena occurring in the designed object.

Regardless of the mathematical apparatus (algebraic, ordinary differential, integral, partial differential equations, etc.), OMM can be represented symbolically as follows:

where  X ⃗={x ⃗,u ⃗ };L(B ⃗,X ⃗) – the operator defining the model’s system of equations.

#### Aerospace Industry and Propulsion Advancements – A Teaser for the Farnborough International Airshow

Due to technological advancements in the aerospace industry, air transportation has become the primary means of travelling. This begs the question of “what are the key factors that could push the industry to the next level and allow for higher performance, low cost and low carbon emission flights?”

For a low carbon aviation to be achieved, a lot of effort is currently put on the aircraft-propulsion integration. Low-pressure-ratio fans are one of the concepts that is being studied in this regard. The lower the pressure across the propulsive element the more the exhaust velocities will decrease and therefore the higher the propulsive efficiency will be. However, a constant level of thrust would require an increase of the fan area, which could lead to an increase of the total weight of the configuration and ultimately cancel the efficiency benefits of the concept.

#### Organic Rankine Cycles: Low Temperature, High Efficiency

Nowadays the scientific community is strongly concerned about problems of efficiency increase and emissions reduction in power generation, ship, and vehicle drives such as internal combustion engines (ICE). A system utilizing waste heat recovery (WHR) is an effective solution for the aforementioned problems.

ORC (meaning organic Rankine cycle, not the scary monsters from Lord of the Rings) is one WHR solution which delivers additional power from the turbine/engine exhaust gas/steam energy.  ORC systems operate on hydrocarbon-based fluids which effectively avoid the typical disadvantages associated with water-based steam turbine systems while bringing the advantage of better performance at part load and in non-continuous operation. ORC systems, capable of utilizing low temperature heat sources of 100-200°C, can be designed in compact and modular packages which require very little maintenance.

The design criteria of an ORC system and its components includes finding the maximum possible heat recovery from the available high and low temperature waste heat flows of a turbine or ICE to produce the maximum amount of additional power while decreasing the load on the turbine’s cooling system, under certain restrictions like geometry and cost.

The first step is to design the thermodynamic cycle configuration. Figure 1 is a flow diagram of a dual loop supercritical organic Rankine cycle (SORC) with separate turbines and given design parameters of the components, generated with AxCYCLE™ software, developed by SoftInWay. The cycle consists of 6 heat exchangers, 2 turbines (HPT and LPT), 2 pumps (HPP and LPP) and the condenser. Both turbines operate with the same backpressure – 1.3 bars. The flows of the working fluid (R245fa in this case) are mixed at the condenser inlet and split at its outlet. The temperature – entropy diagram for the presented cycle is shown on Figure 2. The process 1-2-3-4-5-1 corresponds to the high pressure loop operation and the process 10-20-30-40-10 is for the low pressure loop operation. All these can be easily manipulated and obtained with user-friendly interface of AxCYCLE™.

In terms of component design, ORC turbines can be of axial, radial inflow and radial outflow configurations. The type of turbine you should select depends on the application. To delve further into the topic, check out  SoftInWay’s webinar on “Radial Inflow versus Outflow Turbines – Comparison, Advantages and Applicability” here – http://learn.softinway.com/Webinar/Watch/102

#### Birth, Fall and Resurgence of Gas Turbine Technology for Trains

We as human kind have always aimed at achieving something better, something bigger. This led to the research on gas turbines, which was mainly inspired due to the immediate requirement in the aerospace and power generation industry, to also look beyond the scope of aeronautics.

Today gas turbine technology is often used when dealing with aerospace and power generation industries, but believe it or not, gas turbine technology has been used in ground transportation too;  notably locomotives.

### The Early Applications

After the first world war, several countries had the expertise and the finances to invest in achieving the technological edge in the new post war era. The gas turbine technology was one such technological endeavor, and by the mid-20th century the gas turbine could be found in several applications. Birth of gas turbine locomotives can be credited to two distinct characteristics of these locomotives versus the contemporary diesel locomotives. First, there are fewer moving parts in a gas turbine, decreasing the need for lubrication. This can also potentially reduce the maintenance costs. Second, the power-to-weight ratio is much higher for such locomotives which makes a turbine of a given power output physically smaller than an equally powerful piston engine, allowing a locomotive to be powerful enough without being too bulky.

### Introduction

A pump is a hardware, which feeds energy to a fluid (e.g. Water) to flow through channels. Pumps are used, for example, to direct water out of the ground, to transport drinking or sewerage water over large distances in combined pipe networks or to discard water from polders. In any practical application, the pump needs to work with its best performance. It is also important to check that the flow rate and head of the pump are within the required specifications, which are normally presented as the Pump Characteristic curves. These plots play an important role in understanding the region in which the pump needs to be operated thus ensuring the life of the pump.

### Pump Characteristic Curves

The performance of any type of pump can be shown graphically, which can be based on either the tests conducted by the manufacturer or the simulations done by the designer. These plots are presented as Pump Characteristic Curves. The hydraulic properties of any pump (e.g. Centrifugal Pump) can be described by the following characteristics.

1. Q-H Curve
2. Efficiency Curve
3. Net Positive Suction Head (NPSH) Curve

#### Q-H Curve

The Q-H curve gives the relation between the volume flow rate and the pressure head, i.e. the lower the pump head, the higher the flow rate. Q-H curves are provided by the manufacturer of the pump and can normally be considered as simple quadratic curves.

#### Can a sales team select the right turbomachinery for a client without bothering the engineering team?

This might seem like a strange question, but we get ask this a lot. The question takes the form of: Can the sales side do a proper preliminary design and select the optimal machine (turbine/compressor/pump)?  Is it possible for the design and application task to be integrated in a way allowing the application team the autonomy to make decisions without going back to the engineering team every time they get an inquiry? After realizing how large of a pain point this is for our clients, we decided to solve this problem for a major turbine manufacturer in Asia and in the process, provided a time-saving solution to maximize the returns for all the stakeholders.

The challenge came with the different competencies of the sales and design team. The sales/application teams are not necessarily experts in design while designers cannot double as application engineers to meet the sales requirements.

In our efforts to solve this issue, we worked with this turbine manufacturer. We listed all of their current processes, limitation, requirements, constraints, and etc. to explore the many possible ways to resolve this pain point. In the end, there were two solutions; (1) Develop custom selection software, or (2) Leverage the AxSTREAM® platform using AxSTREAM ION™.

1. Developing Custom Selection Software: Developing a custom selection software specific to the manufacturer where their application team can choose the optimal turbine based on expected customer needs. Developing such a custom system requires bringing together the expertise of different teams from turbomachinery (such as aero-thermal and structural) to software developer, testing, etc. Developing such a one-off system also takes considerable time at considerable cost. This approach could solve the current problem, but with rapidly changing technologies and market requirements, this is not a viable long-term solution.
2. Leverage the AxSTREAM® Platform using AxSTREAM ION™: We evaluated the limitation and possibilities of utilizing our turbomachinery design platform AxSTREAM® to meet the requirement of sales/application engineering team for today’s needs and in the future. We found the organization had a greater advantage using this existing platform rather than investing in the short-term solution of developing a custom selection software. Many of the building blocks required for customization are already available to use via an interface a non-technical sales person could easily use. This platform was utilized for meeting the requirement of this turbine manufacturer saving time and cost while resolving a large pain-point for the organization.

#### Clean Energy

As turbomachinery engineers, it is not always easy to tell non-technical folks what we do. If we start with “I design turbines,” the first thing most people think of are those giant wind turbines, and we are stuck with the nickname “wind guy/gal”. What we do is far more complex than putting 3 blades on a stick and confusing bystanders with why the turbine is rotating on a seemingly windless day; and don’t even get me started on the claims that wind turbines are a non-visually pleasing ploy from the government to make use of our taxpayers money.

Okay, maybe I will get started on those topics, but not in this series. Today, I am introducing a new series of blog posts related to clean energies and how turbomachines tie in with this not-so-novel concept making a lot of noise nowadays.

Throughout this series, we will be discussing the different “clean” technologies in power generation which people have been using for hundreds of years, some more recent “hipster-y” applications, and look at what could make a difference in tomorrow’s world. These short posts will cover general and practical information, which students as well as seasoned engineers can use to better understand the topic at hand. Some articles/parts will be more technical than others, and no matter what your current level of proficiency, you will be able to pick out some useful takeaways.