Conventional Turbomachinery Research Articles

Using Fluid Curtains to Improve Sealing Performance in Turbomachinery Applications

Abstract The results from an investigation into the physics of how fluid curtains can be applied to improve the aerodynamic performance of conventional turbomachinery shaft and rotor seals are described in this paper. Computational fluid dynamics and testing on two experimental facilities are used in the study. In the first part of the work, computational fluid dynamics simulations validated against experimental test data demonstrate the fundamental mechanism by which the presence of the curtain can act to reduce leakage flow through conventional seals. These results are consolidated into a single performance carpet map, showing how the leakage reduction performance and the curtain supply pressure needed to achieve it vary with changes in values of key geometrical parameters. In the second part of the work the effect of swirl in the seal inlet flow, as is often encountered in turbomachinery applications, on the performance of the fluid curtain is investigated experimentally. Test results show that if the swirl momentum in the inlet flow is greater than the momentum of the curtain flow, the performance benefit from applying the curtain is greatly diminished. Overall, the results provide some fundamental design rules for applying fluid curtains to enhance turbomachinery sealing performance for the general type of leakage path geometry (cylindrical channel, 45-deg jet angle, curtain upstream of a conventional seal) and working fluid type and conditions (air, ambient temperature, subsonic leakage channel flow) used in the study.

Design method for a bidirectional ducted tidal turbine based on conventional turbomachinery methods

Renewable energy sources include solar, wind, hydro, geothermal and biomass. Furthermore, ocean energy is being rapidly harnessed worldwide. In this study, to establish a suitable design method for various bidirectional ducted tidal turbines, instead of using blade element momentum theory and CFD, which have been used previously, the method used for turbomachinery was used for designing the turbines. A bidirectional turbine optimises the equipment design and reduces manufacturing and maintenance costs. Using the turbine power as the design condition, the difference in the tangential velocity between the front and rear of the turbine was calculated using Euler’s equation, and the blade stagger angle was determined based on the potential flow theory. To incorporate the effect of duct geometry into this design method in the future, the effect on the internal flow of the duct was experimentally investigated using three ducts with different maximum cross-sectional areas. Performance tests showed that the duct geometry had a negligible effect on the flow rate through the turbine. Therefore, the larger the maximum diameter of the duct, the greater the flow rate into the outside of the duct. The pressure difference between front and rear of the turbine and the inflow energy into the duct were different due to the energy conversion as the flow turned outside of the duct. To improve the accuracy of the design method, the effect of flow at the duct inlet and the energy conversion should be incorporated, and a review of the estimation method for the axial velocity ratio and the selection method for the design representative value should be conducted.

Acoustic signature analysis of a bladeless blower

There has always been a concern about acoustic emissions in traditional machinery. For example, in the transportation and power generation sectors, the market demands efficient, compact, lightweight, and low-cost devices with very low noise levels. In such a challenging context, as opposed to conventional turbomachinery, Tesla type bladeless fluid machine has the advantage of reducing the overall noise emissions level.The originality of this paper lies in its experimental acoustic signature characterization of a Tesla type bladeless blower, which has never been done before, nor is there any comparison to conventional blowers. A tailored experimental setup is described in order to evaluate the acoustic behavior of Tesla blower prototypes at different rotational speeds and distances. To achieve an accurate acoustic characterization, several measurement methods, as well as post-processing techniques, have been evaluated and compared.The results of this study have been compared with those obtained by conventional blowers, while considering the same tip speeds at different distances. A Tesla blower does not exhibit the blade passage phenomenon, as opposed to a conventional blower. A significant contribution of acoustic energy can thus be avoided which is due to its characteristic frequency and its harmonic components, which instead are significant in conventional turbomachinery overall acoustic noise.As a result of this innovative investigation, it has been determined that the air Tesla blower is significantly quieter than conventional dynamic machines, thus paving the way to novel applications for bladeless machinery, especially in those cases aimed at achieving a heightened level of acoustic comfort.

Non-Dimensional Parameters for Comparing Conventional and Counter-Rotating Turbomachines

Abstract Counter-rotating turbomachines have the potential to be high efficiency, high power density devices. Comparisons between conventional and counter-rotating turbomachines in the literature make multiple and often contradicting conclusions about their relative performance. By adopting appropriate non-dimensional parameters, based on relative blade speed, the design space of conventional machines can be extended to include those with counter-rotation. This allows engineers familiar with conventional turbomachinery to transfer their experience to counter-rotating machines. By matching appropriate non-dimensional parameters, the loss mechanisms directly affected by counter-rotation can be determined. A series of computational studies are performed to investigate the relative performance of conventional and counter-rotating turbines (CRTs) with the same non-dimensional design parameters. Each study targets a specific loss source, highlighting which phenomena are directly due to counter-rotation and which are solely due to blade design. The studies range from two-dimensional blade sections to three-dimensional finite radius stages. It is shown that, at hub-to-tip ratios (HTRs) approaching unity, with matched non-dimensional design parameters, the stage efficiency and work output are identical for both types of machines. However, a CRT in the study is shown to have an efficiency advantage over a conventional machine of up to 0.35 percentage points for a HTR of 0.65. This is due to differences in absolute velocity producing different spanwise blade designs.

Brush Seal Frictional Heat Generation—Test Rig Design and Validation Under Steam Environment

Sealing technology is a key feature to improve efficiency of steam turbines for both new power stations and modernization projects. One of the most powerful sealing alternatives for reducing parasitic leakages in the blade path of a turbine as well as in shaft sealing areas is the use of brush seals, which are also widely used in gas turbines and turbo compressors. The advantage of brush seals over other sealing concepts is based on the narrow gap that is formed between the brush seal bristle tips and the mating rotor surface together with its radial adaptivity. While the narrow gap between the bristle tips and the rotor leads to a strongly decreased flow through the seal compared with conventional turbomachinery seals, it is important to be aware of the tight gap that can be bridged by relative motion between the rotor and the brush seal, leading to a contact of the bristles and the rotor surface. Besides abrasive wear occurrence, the friction between the bristles and the rotor leads to heat generation which can be detrimental to turbine operation due to thermal effects, leading to rotor bending connected to increasing shaft vibrations. In order to investigate the frictional heat generation of brush seals, different investigation concepts have been introduced through the past years. To broaden the knowledge about frictional heat generation and to make it applicable for steam turbine applications, a new testing setup was designed for the steam test rig of the Institute of Jet Propulsion and Turbomachinery—TU Braunschweig, Germany, enabling temperature measurements in the rotor body under stationary and transient operation in steam by using rotor-integrated thermocouples. Within this paper, the development of the instrumented new rotor design and all relevant parts of the new testing setup is shown along with the testing ability by means of the validation of the test rig concept and the achieved measurement accuracy. First results prove that the new system can be used to investigate frictional heat generation of brush seals under conditions relevant for steam turbine shaft seals.

Feasibility and operating costs of an air cycle for CCHP in a fast food restaurant

This work considers the possibilities of an air-based Brayton cycle to provide the power, heating and cooling needs of fast-food restaurants. A model of the cycle based on conventional turbomachinery loss coefficients is formulated. The heating, cooling and power capabilities of the cycle are extracted from simulation results. Power and thermal loads for restaurants in Knoxville, TN and in International Falls, MN, are considered. It is found that the cycle can meet the loads by setting speed and mass flow-rate apportionment between the power and cooling functional sections. The associated energy costs appear elevated when compared to the cost of operating individual components or a more conventional, absorption-based CHP system. A first-order estimate of capital investments is provided. Suggestions for future work whereby the operational costs could be reduced are given in the conclusions.

Modeling Contra-Rotating Turbomachinery Components for Engine Performance Simulations: The Geared Turbofan With Contra-Rotating Core Case

This paper presents a method of modeling contra-rotating turbomachinery components for engine performance simulations. The first step is to generate the performance characteristics of such components. In this study, suitably modified one-dimensional mean line codes are used. The characteristics are then converted to three-dimensional tables (maps). Compared to conventional turbomachinery component maps, the speed ratio between the two shafts is included as an additional map parameter and the torque ratio as an additional table. Dedicated component models are then developed that use these maps to simulate design and off-design operation at the component and engine levels. Using this approach, a performance model of a geared turbofan with a contra-rotating core (CRC) is created. This configuration was investigated in the context of the European program “NEW Aero-Engine Core Concepts” (NEWAC). The core consists of a seven-stage compressor and a two-stage turbine without interstage stators and with successive rotors running in the opposite direction through the introduction of a rotating outer spool. Such a configuration results in a reduced parts count, length, weight, and cost of the entire high pressure (HP) system. Additionally, the core efficiency is improved due to reduced cooling air flow requirements. The model is then coupled to an aircraft performance model and a typical mission is carried out. The results are compared against those of a similar configuration employing a conventional core and identical design point performance. For the given aircraft-mission combination and assuming a 10% engine weight saving when using the CRC arrangement over the conventional one, a total fuel burn reduction of 1.1% is predicted.

The Influence of Shear Layer Turbulence on Stationary Pseudoblades in Supersonic Pressure Exchange Inducing Flow Fields

The pressure exchange process can be initiated by nonsteady pressure forces that arise due to moving fluid dynamic interfaces in the laboratory frame of reference. The fluid interfaces are flow features of “pseudoblades” that can be generated by an expanding supersonic primary flow, impinging on freely spinning cone-vane type of rotors. These pseudoblades are fluidic vanes that interface with an entrained, compressible secondary fluid and can mimic the action of impellers as in conventional turbomachinery. The overarching goal of this research is the development of a novel fluid impeller-based ejector. The authors’ motivation towards this study was in understanding the boundary conditions leading to spatial deterioration of pseudoblades. Flow around stationary, axisymmetrically aligned rotors (the ramp vane and double cone type), held in a primary supersonic flow field (Mach 1.44 jet), were investigated by laser Doppler velocimetry (LDV) measurements of shear layer turbulence intensity (TI) under alternative seeding of primary and entrained secondary flows. Rotors were tested and compared for shear layer TI distribution-based boundary conditions, anticipated pseudoblade conditions and an “effective persistence length of stationary pseudoblades.” The results suggest that the double cone rotor is most conducive for pseudoblade stability. The TI distribution-based boundary conditions for this rotor indicate that the effective pseudoblade persistence length approximately equals the exit diameter of the supersonic nozzle.

A comparison of the process integration of shockwave CO2 compression with conventional turbo machinery into PCC power station design

Abstract This paper discusses the energy penalty of solvent based post combustion capture for three different power stations and includes a comparison of shockwave CO 2 compression versus conventional turbo machinery on the energy penalty associated with carbon capture and storage. This study uses pinch analysis to determine targets for the energy penalty of three different power stations that include a brown coal power plant with no reheat stage, a more efficient brown coal power station and a black coal power station. Heat integration can be used to reduce the energy penalty of all power stations combined with CCS. It is also found that when heat integration is considered, the heat that can be recovered in shockwave compressor inter/after-coolers reduces the amount of steam that needs to be extracted from the steam turbine. Hence, the net power output from the power station will be higher when shockwave compressors are used for CO 2 compression compared to conventional turbo-machinery.

Crypto-steady supersonic pressure exchange: A simple analytical model

This paper is motivated by a long-range goal of developing a new class of turbomachine where fluid impellers, created through supersonic wave structures, replace mechanical impellers. This paper is an exploratory study to show how effectively supersonic wave structures can fulfill this goal, and to provide some fundamental insight as to the behavior. A comparison, at a fundamental level, of the spectrum of flow induction devices from mechanical turbomachinery to direct flow induction including steady flow ejectors, wave rotors, and pressure exchange devices is explored. While the authors have been studying various flow induction devices intended to lead to practical solutions, the details of the flow interactions are obscured by geometries and the complex interactions. This paper attempts to take a step backward and look at the simplest conceivable model that demonstrates the phenomena thought to be the key to a new technology. This model is a crypto-steady supersonic pressure exchange process occurring behind a supersonic frictionless semi-infinite flat plate having a pressure differential between both sides of the plate. It is found that very high compressor efficiencies and energy transfer rates are possible even with the presence of supersonic flow structure. Because of the high efficiencies, the analysis shows that there is a potential for the development of a new generation of direct flow induction devices far simpler and more compact than conventional turbomachinery, yet far more efficient than conventional ejectors and wave rotors. Fundamental information is provided which will facilitate exploiting supersonic pressure exchange in practical crypto-steady flow induction devices.

Crypto-steady supersonic pressure-exchange: A simple analytical model

This paper is motivated by a long-range goal of developing a new class of turbo-machines, where fluid impellers, created through supersonic wave structures, replace mechanical impellers. This paper is an exploratory study to show how effectively supersonic wave structures can fulfil this goal, and to provide some fundamental insight as to the behavior. A comparison, at a fundamental level, of the spectrum of flow-induction devices from mechanical turbo-machinery to direct flow induction including steady-flow ejectors, wave rotors, and pressure-change devices is explored. While the authors have been studying various flow-induction devices intended to lead to practical solutions, the details of the flow interactions are obscured by the geometries and the complex interactions. This paper attempts to take a step backward and look at the simplest conceivable model that demonstrates the phenomena thought to be the key to a new technology. This model is a crypto-steady supersonic pressure-exchange process occurring behind a supersonic frictionless semi-infinite flat-plate having a pressure differential between both sides of the plate. It is found that very high compressor efficiencies and energy-transfer rates are possible, even with the presence of a supersonic-flow structure. Because of the high efficiencies, the analysis shows that there is potential for the development of a new generation of direct-flow induction devices far simpler and more compact than conventional turbomachinery, yet far more efficient than conventional ejectors and wave rotors. Fundamental information is provided which will facilitate exploiting supersonic pressure-exchanges, in practical crypto-steady flow-induction devices.

On Cross-Flow Fan Theoretical Performance and Efficiency Curves: An Energy Loss Analysis on Experimental Data

Contrary to conventional turbomachinery, cross-flow fan flow field is non-axisymmetrical and its complex configuration strongly affects performance and efficiency characteristic curves. The formulation of a theory on cross-flow fan operation is made even tougher since the strength and the eccentricity of the vortex that forms within the impeller are deeply influenced by the geometry of the impeller and of the casing as well. In this paper, a numerical reconstruction of the flow field, validated against an extensive systematic database of global and local experimental measurements, is analyzed. The aim is to achieve a general interpretation of performance and efficiency curves, and to lead them back to one theoretical archetype, whatever the fan configuration being considered.

Semi-analytical techniques for investigating thermal non-equilibrium effects in wet steam turbines

This paper describes a semi-analytical solution of the polydispersed wet stream equations, valid in regions where the nucleation rate is negligible. The solution can be used in conjunction with any conventional turbomachinery calculation procedure to obtain estimates of the magnitude of departures from thermal equilibrium. For example, from an initial estimate of the pressure distribution, it is a simple matter to calculate the distribution of supercooling and wetness fraction, together with the thermodynamic losses incurred by the flow. The method differs from the usual numerical approach by providing general results which give considerable physical insight. Computational time and effort is also dramatically reduced. The controlling parameters emerge naturally from the analysis, and information concerning the fundamental fluid mechanics of wet steam is revealed. In particular, the analysis demonstrates the role played by the thermal relaxation time and the rate of expansion in controlling the deviation from equilibrium. The versatility and usefulness of the technique in furnishing results for the turbine designer are demonstrated by a number of applications including one-dimensional nozzle flows and two-dimensional blade-to-blade and hub-to-tip flows. In each case it is shown how the droplet size and expansion rate influence the thermodynamic losses and other flow variables of interest.