As a thermodynamic Brayton cycle, the performance of the gas turbine engine is influenced by the turbine inlet temperature, and the raise of this temperature can lead to better performance and more efficient machines. Current advancements in the development of cooling systems allows most modern gas turbines to operate in temperatures much higher than the material melting point. Of course nothing would have been possible without the parallel development of advanced materials for structural components as well as advances in computing resources and consequently in aerodynamic design, prognostic and health monitoring systems and lifing processes. In particular, as far as the lifing of the machine is concerned, the high pressure (HP) turbine containing the most advanced high temperature alloys and associated processing methods, as well as the combustor which represents the key components that have limited life and tend to strictly dictate the cycles of operation and the allowable time on the wing.
IGVs are a series of blades circumferentially arranged at the inlet of compressor, driven electronically or pneumatically.By adjusting the orientation of IGVs, the air flow enters the impeller at a different direction therefore changing the flow behavior while affecting the passing mass flow rate (throttling). This can effectively reduce the power consumption to increase the compressor’s overall efficiency while avoiding surge to provide a better off design working range.
The designer needs to optimize blade profile and positioning of the IGV for efficient operation of a compressor, which can be a tedious job if one does not have a handy tool. Figure 1 shows an example of IGV working on different angles.
In AxSTREAM, people are able to add IGV component before the centrifugal compressor impeller which can provide different ways to edit its profile such as: Read More
Thermal energy storage can be achieved with widely diverse technologies, including molten salt application. By heating the salt and storing it in insulated containers, users can pump out the salt to release the heat stored when the energy is needed. For example, with solar application the molten salt stores the excess heat that is produced during the day and releases it at night to produce electricity.
Looking to solve the problem of range anxiety in electric vehicles, many companies have started exploring the business model of recharging electric batteries in automotive vehicles with a parallel turbine engine driving a generator – coined under the term ‘micro-turbine range extender’ (or MTRE). As seen in the turbine-powered car programs initiated in the 50s and 60s, issues with low efficiencies, slow throttle response, and capital cost of the powertrain rendered all of these programs futile shortly after their inception. However, the revolution of electric vehicles and hybrid technologies has allowed this technology to resurface from a different direction. With battery-driven electric motors designated as the main driver, these cars are equipped with a technology that has both energy efficient low-end torque as well as groundbreaking throttle response and many of the former drawbacks during its initial iterations are solved using an electric drivetrain. The turbine-engine, instead of operating as the main driver, will now only operate at its most efficient power output mode and work to simply drive electricity through the generator, recharging the vehicle’s battery packs. Acting as an isolated thermo-mechanical system, a micro-turbine range extender can be designed and optimized without having to worry about the varying duty cycles and idling that is inherent in the vehicle’s drivetrain. The thermodynamic model of a typical micro-turbine range extender can be seen below in Figure 1.
One application within commercial vehicles that has benefitted from this technology utilizes a MTRE system developed by Wrightspeed. The specific application lies within retrofitting refuse trucks with this electric powertrain in order to help them save an estimated $35,000 a year on fuel and maintenance costs. In such heavy-duty applications, it is obvious that the potential for fuel cost and maintenance savings is much higher due to the large fuel burning needed for these vehicles as well as the harsh drive cycle a refuse truck goes through. The question in the expansion of this technology generally comes in two forms: What makes the micro-gas turbine range extender a better alternative than a normal ICE hybrid option? – and – What is the viability of scaling this for consumer vehicles given the capital cost of the drivetrain?
To go back to the question, blade tip losses represent a major efficiency penalty in a turbine rotor. These losses are presently controlled by maintaining close tolerances on tip clearances. Tip leakage resulting by gaps between the blade tip and the casing can account for about 1/3 of the total losses in a turbine stage. The reason is mainly the offloading of the tip since the leaking fluid is not exerting a force on the blade, as well as the generation of complicated flow further downstream due to the leakage vortex.
Typically, supersonic turbine consists of supersonic nozzles with a subsonic inlet and one or two rows of rotating blades. The turbine usually has partial arc admission. The total flow could go through either a single partial arc or several ones. The latter is typical for a steam turbine control stage or standalone applications. The inlet manifold or nozzles chests, as well as exhaust duct, are critical parts of the turbine as well. Due to the very frequent application of partial admission, it is not possible to implement any significant reaction degree. Thus, this kind of turbine is almost always an impulse type. However, some reaction degree could still be applied to full admission turbines. The influence of the rotor blades profile designed for high reaction degree on rotor-stator supersonic interaction and turbine performance is not well studied at the moment.
One of the most challenging tasks during turbomachinery design is the definition of aerodynamic shape of the blades, taking into account the complicated flow phenomena and the effect that the shape will have to other disciplines of the design. The rapid increase of computational resources along with the development of CFD has led to a big interference of optimization methods and numerical simulations as part of the design process. There are two main categories in which optimization methods fall: the stochastic models and the gradient-based models. The first family of models focuses on finding the optimum design, while the second uses the gradient information to lead the optimization. Apart from the optimization algorithms, there are several techniques that help designers understand the dependence of design parameters towards others and extract meaningful information for the design. First, the design of experiment approach (DoE) consists of the design of any task that aims to describe or explain the variation of information for conditions that are hypothesized to reflect the variation. Next, we have the surrogate models that are used instead of the optimization algorithms to generate a model that is as accurate as possible while using as few simulation evaluations as possible with low computational cost. The most common surrogate models used for turbomachinery design are the Response Surface Method, the Kriging Model and the Artificial Neural Networks. Last, data mining approaches have recently become very popular as they allow engineers to look for patterns in large data sets to extract information and transform it into an understandable structure for further use.
As far as the aerodynamic design optimization methods is concerned, they can be grouped into inverse and direct designs. Inverse methods rely on definition of pressure distribution and they iterate along blade shape, changing to develop a final profile shape. The computational cost is low and such methods can be combined with an optimization method in an efficient design process. However, the biggest disadvantages lies on the fact that this approach is strongly dependent on the experience of the designer. Young engineers may fail to define a pressure distribution that performs well in design and off-design conditions. In addition, with the inverse method approach the user cannot account for geometric and mechanical constraints.
Centrifugal compressors span a number of applications including oil compression systems, gas shift systems, HVAC, refrigeration, and turbochargers. It works by using energy from the flow to raise pressure, using gas to enter the primary suction eye (impeller). As the impeller rotates, the blades on the impeller push the gas outwards from the center to the open end of impeller to form a compression. Compressors are commonly used for combustion air supplies on cooling and drying systems. In HVAC system application, fans produce air movement to the space that is being conditioned. As a key component of an energy cycle, design/performance requirement must be met. While a design can easily be scaled from an existing design through appropriate parameters, a tailored design from scratch to confirm with design requirement for the specific cycle would give a better match and improve overall cycle performance.
There are variants of non-aerodynamic constraints in centrifugal compressor design practice, from frame size to durability and ultimately cost. An optimized impeller design should also ensure that aerodynamic problems associated with the all compressor components are minimized. With all of these (aerodynamic and non-aerodynamic) design constraints, there is no better way to optimize your compressor design than starting from the preliminary step, making sure that your compressor meets your criteria from a one dimensional basis ( a step that is often overlooked in practice).
Several decades later, we are seeing a resurgence of turbine motors in automobiles, but now serving as a range extender generator for electric vehicles instead. As with many upcoming technologies, learning from past research and failed historical attempts can bring light to the most elegant and innovative solutions for today’s modern challenges. This revolution of an old concept shares many of the qualities that made turbine engines attractive back in its initial development phase. Such advantages include the ability to run on any flammable liquid and the high power density that results in a significantly lower weight and size contribution than its piston engine counterpart.
Over the years, as steam turbine technology advanced, the design principles were based on either impulse type or reaction type with reaction type being more efficient. Though impulse was not as efficient as reaction type, it gained popularity due to lower cost and compact size. With advances in design and optimization methods being employed, the efficiency levels between these two types are not very distant, ranging between 2 – 5% based on the size and application. Read More