Author: Taras Hryshchenko

An Introduction to Pipe Diffusers in Centrifugal Compressors

Posted by Taras Hryshchenko

A pipe diffuser is a special type of radial vane diffuser and is widely used in centrifugal compressors of gas turbine engines. Employing pipe diffusers can lead to increased efficiency in centrifugal compressors by an average of 2-4% compared to other vaned diffusers. The efficiency gains are especially prominent at high-pressure ratios (over 5.0), toward which we are seeing a growing trend in gas turbine engines.

Pipe Diffuser and assembly
Figure 1 (left): Single flow path of pipe diffuser & Figure 2 (right): Pipe diffuser assembly

Figure Source: Stanislaw Antas, Exhaust System for Radial and Axial-Centrifugal Compressor with Pipe Diffuser, Int J Turbo Jet Eng 2016;

Pipe Diffuser Geometry

The initial part of a pipe diffuser is a cylindrical section (throat), followed by the conical diffuser (Figure 3). The axis of the pipe diffuser must be tangent to the circle created by the tip of the centrifugal compressor, i.e., the circle defined by the impeller tip radius R2. The leading edge of the pipe diffuser channel is elliptical due to the oblique intersection of the cylindrical throat with the cylindrical surface of the diffuser radius R3. This intersection design results in gradually adapting the effluent flow from the impeller to the flow through the cylindrical and conical sections of the diffuser. The downstream duct of a compressor with a pipe diffuser is a diffusing trumpet, also called a “fishtail” diffuser. Read More

Compressors in Fuel Cell Systems

Posted by Taras Hryshchenko

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As we covered in our previous blog about fuel cell systems, a large contributor to their efficiency is the compressor that is selected for it. But what are the different kinds of compressors, and which one is best for a specific system?

Compressors have a wide variety of designs and types, which differ in pressure and performance, depending on the kind of compressed fluid. Compressors are also classified according to the type of work: dynamic and positive displacement. Figure 1 shows the types and classification of compressors.

Figure 1 Compressor Types
Figure 1: Compressor Types. Source: Dongdong Zhao, “Control of an ultrahigh-speed centrifugal compressor for the air management of fuel cell systems” 5 Jun 2014, p. 8.

Figure 2 shows a comparison of various types of compressors according to several criteria: generated pressures, occupied volume, lubrication requirements, compressor weight, and pressure ripples at the outlet.

Comparisons of Compressors
Figure 2: Comparison of Compressors. Source: Dongdong Zhao, “Control of an ultrahigh-speed centrifugal compressor for the air management of fuel cell systems” 5 June 2014, p. 13.

As can be seen from the comparison above, we can conclude that centrifugal compressors offer a number of advantages over its positive displacement counterparts:

  1. Lightweight;
  2. Small volume;
  3. Only the bearings require lubrication;
  4. Creates a sufficiently high pressure (1.5…6 bar);
  5. Has high efficiency (80…82%); and
  6. Has a fairly wide performance range.

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Next, we will consider the application of the centrifugal compressor in the fuel cell system. Read More

An Introduction to Fuel Cells: What Are They, How Do They Work, and How Can We Improve Their Efficiency?

Posted by Taras Hryshchenko

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Alternative energy based on the use of fuel cells is gaining more and more popularity and is increasingly being used in the automotive, aerospace, and energy industries as well as other sectors of the economy.

What is a Fuel Cell?

Fuel cells (FC) are electrochemical devices which convert the chemical energy of a fuel directly into usable energy – electricity and heat – without combustion. This is quite different from most electricity-generating devices (e.g., steam turbines, gas turbines, reciprocating engines), which first convert the chemical energy of a fuel to thermal energy via combustion, then into mechanical energy, and finally to electricity.

Fuel cells are similar to batteries containing electrodes and electrolytic materials to accomplish the electrochemical production of electricity. Batteries store chemical energy in an electrolyte and convert it to electricity on demand until the chemical energy has been depleted.

Fuel cells do not store chemical energy. Rather, they convert the chemical energy of a fuel into electricity. Thus fuel cells do not need recharging, and can continuously produce electricity as long as fuel and an oxidizer are supplied.

A prototype fuel cell is shown below in Figure 1.

Fuel Cell
Figure 1: Fuel Cell. Source

What is the operating principle of a fuel cell?

Today, there are two types of electrolytes used in fuel cells: acid or alkali. The type also depends on the chemical reactions that take place in the element itself. Read More

Integrated Design and Analysis of Turbofan Engines

Posted by Taras Hryshchenko

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