This paper investigates the impact of the oil (silicone oil PSF-5cSt) presence in the air on the leakage and rotordynamic characteristics of a long-honeycomb seal with length-to-diameter ratio L/D = 0.748 and diameter D = 114.656 mm. Tests are carried out with inlet pressure P i = 70.7 bars, pressure ratio (PR) = 0.35 and 0.25, inlet liquid volume fraction (LVF) = 0%, 3.5%, and 7%, and shaft speed ω = 10, 15, and 20 krpm. During the tests, the seal is centered. Test results show that leakage mass flow rate m ˙ increases (as expected) as inlet LVF increases. Increasing inlet LVF makes direct stiffness K increase more rapidly with increasing excitation frequency Ω. Increasing inlet LVF has a negligible effect on K at low Ω values, but increases K at high Ω values. The value of effective damping C eff at about 0.5 ω is an indicator to the system stability since an unstable centrifugal compressor rotor can precess at about 0.5 ω . Increasing inlet LVF increases the value of C eff at about 0.5 ω , reducing the possibility of subsynchronous vibrations (SSVs) at about 0.5 ω . San Andrés's model is used to produce predictions. The model assumes that the test fluid in the seal clearance is an isothermal-homogenous mixture. The model adequately predicts m ˙ , K, and the value of C eff at about 0.5 ω .

Recent research on turbomachinery design and analysis for supercritical carbon dioxide (sCO 2 ) power cycles has relied on computational fluid dynamics. This has produced a large number of works whose approach is mostly case-specific, rather than of general application to sCO 2 turbomachinery design. As opposed to such approach, this work explores the aerodynamic performance of compressor blade cascades operating on air and supercritical CO 2 with the main objective to evaluate the usual aerodynamic parameters of the cascade for variable boundary conditions and geometries, enabling “full” or “partial” similarity. The results present both the global performance of the cascades and certain features of the local flow (trailing edge and wake). The discussion also highlights the mechanical limitations of the analysis (forces exerted on the blades), which is the main restriction for applying similarity laws to extrapolate the experience gained through decades of work on air turbomachinery to the new working fluid. This approach is a step toward the understanding and appropriate formulation of a multi-objective optimization problem for the design of such turbomachinery components where sCO 2 is used as the operating fluid. With this objective, the paper aims to identify and analyze what would be expected if a common description of such computational design problems similar to those where air is the working fluid were used.

The Blended Blade and End Wall (BBEW) contouring technology can adjust the dihedral angle between suction surface and endwall, thus reducing corner separation in compressors. Generally, the design of BBEW relies on the experiences, the effective design results cannot be the optimal result. In this paper, an optimization approach based on the genetic algorithm (GA) for feature selection and parameter optimization of support vector machine (SVM) is used to obtain the optimal BBEW parameters in a compressor cascade. Based on the sensitivity analysis of the results, it is found that the maximum blended width and the axial position of the maximum blended width are the two most important design parameters. The experimental results show that the optimal BBEW cascade can stretch the spanwise area of the high loss region, and reduce the maximum value in it. The numerical studies were conducted to analysis the flow mechanism. It is shown that the BBEW cascade has a transverse pressure difference at the axial position of the maximum blended width, and magnitude of the pressure difference in proportion to the maximum blended width. The transverse pressure difference remove the low-energy fluid from the corner to the main flow, thus improving the corner separation.

This paper investigates the impact of liquid presence in air on the leakage and rotordynamic coefficients of a long (length-to-diameter ratio L/D = 0.747) teeth-on-stator labyrinth seal. The test fluid is a mixture of air and silicone oil (PSF-5cSt). Tests are carried out at inlet pressure P i = 62.1 bars, three pressure ratios from 0.21 to 0.46, three speeds from 10 to 20 krpm, and six inlet liquid volume fractions (LVFs) from 0% to 15%. Complex dynamic-stiffness coefficients H ij are measured. The real parts of H ij are too frequency dependent to be fitted by frequency-independent stiffness and virtual-mass coefficients. Therefore, this paper presents frequency-dependent direct stiffness K Ω and cross-coupled stiffness k Ω . The imaginary parts of H ij produce frequency-independent direct damping C. Test results show that, under both pure- and mainly air conditions, the leakage mass flowrate m ˙ of the test seal steadily increases as inlet LVF increases. K Ω is negative under all test conditions, and the magnitude of K Ω increases as inlet LVF increases, leading to a larger negative centering force on the associated compressor rotor. Under pure-air conditions, k Ω is a small negative value. Injecting oil into the air increases k Ω slightly and make the magnitude of k Ω closer to zero. Under mainly air conditions, increasing inlet LVF from 2% to 15% has little impact on k Ω . C normally increases as inlet LVF increases. The value of the effective damping C eff = C − k Ω /Ω near 0.5 ω is of significant interest to the system stability since an unstable centrifugal compressor may precess at approximately 0.5 ω . Ω denotes the excitation frequency. The oil presence in the air has little impact on the value of C eff near 0.5 ω . Also, the liquid presence does not change the insensitiveness of m ˙ , K Ω , k Ω , C, and C eff to change in ω ; i.e., under both pure- and mainly air conditions, changes in ω has little impact on m ˙ , K Ω , k Ω , C, and C eff .

Interest in small-scale turbines is growing mainly for small-scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100 W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio, and outlet area of exhaust with speeds ranging from 10,000 rpm to 40,000 rpm. A quasi-one-dimensional (1D) model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, and nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.

Modern aircraft engines combine liquid fuel and air using an intricate flow device with many fuel and air flow passages. To date, the process by which the fuel atomizes within this swirler set has not been examined directly due to optical access limitations. In this work, high-speed X-ray phase-contrast imaging of a liquid spray inside a gas turbine engine swirler geometry is presented. Measurements were carried out at the 7-BM beamline of the Advanced Photon Source at Argonne National Laboratory using the high-energy broadband X-ray beam. The synchrotron X-ray source provides the necessary photon energy and flux to capture time-resolved fluid phenomena within the confines of the relevant geometry while liquid and air are flowing. Spray nozzle hardware and geometries were provided by the National Jet Fuels Combustion Program (NJFCP), allowing for characterization of the spray using a commercially relevant configuration. Modified swirlers were three-dimensional printed with acrylic to improve imaging access while maintaining influential internal features. Water was used as a surrogate fluid for these studies to demonstrate the visualization capabilities. The experiments were conducted at atmospheric exit pressure conditions with a pressure drop of 6% across the swirler. High-speed imaging of the pilot spray cone revealed sheet breakup several millimeters downstream of the orifice exit, upon interaction with the radial assist air flow. These droplets and ligaments were observed to impinge on the inner filming surface of the swirler and flow toward the exit while developing a tangential flow. Under these conditions, the liquid film grows up to several hundred microns in thickness on the filming surface, and subsequently forms ligaments up to several millimeters in length before breaking up. This work demonstrates the capability of X-ray diagnostics in visualizing liquid flows within solid geometries of technical relevance. Furthermore, the spatial quantification of filming flows and liquid interaction with the swirler air provides validation data for modeling of the multiphase flows and surface interactions within the swirler.

This paper describes a large eddy simulation (LES) conducted for a nonadiabatic rotating cavity with a radial inflow introduced from the shroud. The dimensionless mass flowrate of the radial inflow is C w = 3500 and the rotational Reynolds number, based on the cavity outer radius, is equal to Re θ = 1.2 × 10 6 . The time-averaged local Nusselt number on the heated wall is compared with the experimental data available from the literature, and with those derived from the solution of two unsteady Reynolds-averaged Navier–Stokes (URANS) eddy viscosity models, namely, the Spalart–Allmaras and the k − ω shear stress transport (SST) model. It is shown that the Nusselt number is underpredicted in the lower part of the disk and overpredicted in the outer region by both URANS models, whereas the LES provides a much better agreement with the measurements. The behavior results primarily from a different flow structure in the source region, which, in the LES, is found to be considerably more extended and show localized buoyancy phenomena that the URANS models investigated do not capture.

The conventional design of organic Rankine cycle (ORC) power systems starts with the selection of the working fluid and the subsequent optimization of the corresponding thermodynamic cycle. More recently, systematic methods have been proposed integrating the selection of the working fluid into the optimization of the thermodynamic cycle. However, in both cases, the turbine is designed subsequently. This procedure can lead to a suboptimal design, especially in the case of mini- and small-scale ORC systems, since the preselected combination of working fluid and operating conditions may lead to infeasible turbine designs. The resulting iterative design procedure may end in conservative solutions after multiple trial-and-error attempts due to the strong interdependence of the many design variables and constraints involved. In this work, we therefore present a new design and optimization method integrating working fluid selection, thermodynamic cycle design, and preliminary turbine design. To this purpose, our recent 1-stage continuous-molecular targeting (CoMT)-computer-aided molecular design (CAMD) method for the integrated design of the ORC process and working fluid is expanded by a turbine meanline design procedure. Thereby, the search space of the optimization is bounded to regions where the design of the turbine is feasible. The resulting method has been tested for the design of a small-scale high-temperature ORC unit adopting a radial-inflow turbo-expander. The results confirm the potential of the proposed method over the conventional iterative design practice for the design of small-scale ORC turbogenerators.

The Laboratory for Applied Mechanical Design (LAMD) designed, manufactured, and experimentally tested a novel recirculation fan for a 10 kWe solid oxide fuel cell (SOFC). The fan uses oil-free bearings, more specifically herringbone-grooved journal and spiral-grooved thrust gas bearings. The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades with constant height. Prior to coupling the recirculation fan with the SOFC, the fan was experimentally characterized with air at 200 °C. At the nominal point of 168 krpm, the measured inlet mass flow rate is 4.9 kgh-1, the total-tototal pressure rise 55 mbar, the isentropic total-to-total efficiency 55 %, and the power 18.3 W. This paper compares the experimental data towards a computational fluid dynamic simulation of the full fan impeller and volute suggesting an excellent correlation at the nominal point what validates the numerical approach. However, the heat flows crossing the fan fluid domain, have an increased effect at off-design conditions, thus the experimental results need careful consideration. The fan backface leakage has negligible impact on the measurements.

This paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO 2 ) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the past concepts using modular hermetic squeeze film dampers presented, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design in efforts to reduce space envelope, cost, and improve overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Nonrotating benchtop tests show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid–structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and the decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase ultimately affecting dynamic cavity pressures and force coefficients.

A twin-fluid atomizer configuration is simulated by means of the 2D weakly-compressible Smooth Particle Hydrodynamics method, and compared to experiments. The Gas-to-Liquid-Ratio, the momentum flux ratio and the velocity ratio are set constant for different ambient pressures, which leads to different gaseous flow sections. The objectives of this study are to (i) investigate the effect of ambient pressure at constant global parameters, and (ii) to verify the capability of 2D SPH to qualitatively predict the proper disintegration mechanism and to recover the correct evolution of the spray characteristics. The setup consists of an axial liquid jet of water fragmented by a co-flowing high-speed air stream ($U_g$ = 80 m/s) in a pressurized atmosphere up to 16 bar. The results are compared to the experiment, and presented in terms of (i) mean velocity profiles, (ii) drop size distributions and (iii) Sauter Mean Diameter of the spray. It is found that there exists an optimal pressure to minimize the mean size of the spray droplets. Finally, two new quantities related to atomization are presented: (i) the breakup activity that quantifies the number of breakup events per time and volume unit and (ii) the fragmentation spectrum of the whole breakup chain, which characterizes the cascade phenomenon in terms of probability. The breakup activity confirms the presence of the optimal pressure and the fragmentation spectrum gives information on the type of breakup, depending on the ambient pressure.

This paper presents a detailed loss analysis of a centrifugal compressor stage with a vaned diffuser for application in a heavy duty engine turbocharger. The analysis is carried out in order to investigate the loss distribution in the stage. To quantify the impact of different loss types and locations, a detailed validated steady-state 3D CFD solution is employed. The local entropy production rate is calculated for two operating points (full load and part load), which are most relevant to the real world operation of the compressor in a truck application. Two methods are suggested as the procedure for the division of the whole fluid volume into sub-volumes, because this is key for the resulting loss distribution. The primary loss generating mechanisms are shown at main operating conditions to reveal the regions of improvement. A detailed grid study was conducted to enable the calculation of the entropy ratio. It was possible to capture around 78% (partial load) and 70% (full load) of the entropy production with a mesh with circa 100 million elements. Around half of the losses were due to the boundary layer friction, followed by losses associated with a boundary layer separation resulting from the back-flow at the shroud contour close to the impeller exit and back disk friction accounted for with 6-7% of the stage's losses.

The realization of commercial mini organic Rankine cycle (ORC) power systems (tens of kW of power output) is currently pursued by means of various research and development activities. The application driving most of the efforts is the waste heat recovery from long-haul truck engines. Obtaining an efficient mini radial inflow turbine, arguably the most suitable type of expander for this application, is particularly challenging, given the small mass flow rate, and the occurrence of nonideal compressible fluid dynamic effects in the stator. Available design methods are currently based on guidelines and loss models developed mainly for turbochargers. The preliminary geometry is subsequently adapted by means of computational fluid-dynamic calculations with codes that are not validated in case of nonideal compressible flows of organic fluids. An experimental 10 kW mini-ORC radial inflow turbine will be realized and tested in the Propulsion and Power Laboratory of the Delft University of Technology, with the aim of providing measurement datasets for the validation of computational fluid dynamics (CFD) tools and the calibration of empirical loss models. The fluid dynamic design and characterization of this machine is reported here. Notably, the turbine is designed using a meanline model in which fluid-dynamic losses are estimated using semi-empirical correlations for conventional radial turbines. The resulting impeller geometry is then optimized using steady-state three-dimensional computational fluid dynamic models and surrogate-based optimization. Finally, a loss breakdown is performed and the results are compared against those obtained by three-dimensional unsteady fluid-dynamic calculations. The outcomes of the study indicate that the optimal layout of mini-ORC turbines significantly differs from that of radial-inflow turbines (RIT) utilized in more traditional applications, confirming the need for experimental campaigns to support the conception of new design practices.

Dynamic force coefficients are presented from experimental results of a radial gas bearing with hermetically sealed squeeze film dampers (HSFD) in the bearing support. HSFDs are a relatively new technology aimed to increase damping levels in gas bearings while sustaining an oil-free bearing sump. Past HSFD designs proved bulky and contained many components making it difficult to employ in size limited environments such as jet engines, while the diffusion bonded bearing discussed in the present paper provides a compact integral design. Details of the design are found in a companion paper by Ertas [1]. Test results for a three-inch (76.2 mm) diameter bearing using a test rig providing static loads up to 80 lbs (356 N), controlled-dynamic orbital motion, and speeds up to 27 krpm are shown. Results include frequency and speed dependent direct and cross-coupled rotordynamic force coefficients. Dynamic testing showed little dependence on rotor speed or static load and exhibited frequency dependency at lower excitation frequencies. Cross-coupled terms are generally an order of magnitude lower than direct terms. Results show the direct stiffness coefficients increasing with frequency while direct damping decays radically with frequency. Comparison of the overall gas bearing coefficients with the companion paper [1], showing bearing support coefficients, reveals a drastic reduction in damping when engaging the gas film. The results also indicate the bearing can withstand vibration levels representative of a large rotor system critical speed at lower excitation frequencies.

The present work aims to investigate cavitating flows of water, liquid hydrogen and nitrogen on hydrofoils numerically, using the open source code OpenFOAM. The Eulerian homogeneous mixture approach has been used, consisting in a mass transfer model which is based on the combination of a two-phase incompressible unsteady solver with a Volume of Fluid (VOF) interface tracking method. Thermal effects have been introduced by means of the activation of energy equation and latent heat source terms plus convective heat source term. The dependency of the saturation conditions to the temperature has been defined using Antoine-like equations. An extended Schnerr-Sauer model based on the Classical Nucleation Theory (CNT) has been implemented for the computation of the interfacial mass transfer rates. In order to investigate the nucleation effects, an extension of the Classical Nucleation Theory has been considered by coupling the Population Balance Equation/Extended Quadrature-Based Method of Moments (PBE-EQBMM) with the CFD model,which has been defined in combination with a transport equation for the nuclei density. Results showed that nucleation determined a non-uniform field of nuclei density so as to produce a reduction of the temperature drop inside the vapor bubbles, as well as a warmed wake downstream the vapor cavity. Unsteady computations also revealed an influence of the nucleation on the dynamics of the vapor cavity and the bubble detachment.

The identification method using infinitesimal theory is proposed to predict rotordynamic coefficients of annular gas seals. The transient solution combined with moving grid method was unitized to obtain the fluid reaction force at a specific position under different whirling frequencies. The infinitesimal method is then applied to obtain the rotordynamic coefficients, which agrees well with published experimental results for both labyrinth seals and eccentric smooth annular seals. Particularly, the stability parameter of the effective damping coefficient can be solved precisely. Results show that the whirling frequency has little influence on direct damping coefficient, effective damping coefficient, and cross-coupled stiffness coefficient for the labyrinth seal. And the effective damping coefficients decrease as the eccentricity ratio increases. A higher eccentricity ratio tends to destabilize the seal system, especially at a low whirling frequency. Results also show that the fluid velocity in the maximum clearance in the seal leakage path is less than that in the minimum clearance. The inertial effect dominates the flow field. Then it results in higher pressure appearing in maximum clearances. The pressure difference aggravates the eccentricity of rotor and results in static instabilities of the seal system.

The National Jet Fuel Combustion Program (NJFCP) is an initiative being led by the Office of Environment & Energy at the FAA, to streamline the ASTM jet fuels certification process for alternative aviation fuels. To accomplish this, the program has identified specific applied research tasks in several areas. The National Research Council of Canada (NRC) is contributing to the NJFCP in the areas of sprays and atomization and high altitude engine performance. This paper describes work pertaining to atomization tests using a reference injection system. The work involves characterization of the injection nozzle, comparison of sprays and atomization quality of various conventional and alternative fuels, and uses the experimental data to validate spray correlations. The paper also briefly explores the application viability of a new diagnostic system that has the potential to reduce test time in characterizing sprays. Measurements were made from ambient up to 10 bar pressures in NRC's High Pressure Spray Facility using optical diagnostics including laser diffraction, phase Doppler anemometry (PDA), LIF/Mie imaging and laser sheet imaging to assess differences in the atomization characteristics of the test fuels. A total of nine test fluids including six NJFCP fuels and three calibration fluids were used. The experimental data were then used to validate semi-empirical models, developed through years of experience by engine original equipment manufacturers, and modified under the NJFCP, for predicting droplet size and distribution. The work offers effective tools for developing advanced fuel injectors, and generating data that can be used to significantly enhance multidimensional combustor simulation capabilities.

Reactor coolant pump (RCP) is one of the most important equipment of the coolant loop in a pressurized water reactor system. Its safety relies on the characteristics of the rotordynamic system. For a canned motor RCP, the liquid coolant fills up the clearance between the metal shields of the rotor and stator inside the canned motor, forming a long clearance flow. The fluid-induced forces of the clearance flow in canned motor RCP and their effects on the rotordynamic characteristics of the pump are numerically and experimentally analyzed in this work. A transient computational fluid dynamics (CFD) method has been used to investigate the fluid-induced force of the clearance. A vertical experiment rig has also been established for the purpose of measuring the fluid-induced forces. Fluid-induced forces of clearance flow with various whirl frequencies and various boundary conditions are obtained through the CFD method and the experiment. Results show that clearance flow brings large mass coefficient into the rotordynamic system and the direct stiffness coefficient is negative under the normal operating condition. The rotordynamic stability of canned motor RCP does not deteriorate despite the existence of significant cross-coupled stiffness coefficient from the fluid-induced forces of the clearance flow.

Natural gas is traditionally considered as a promising fuel in comparison with gasoline due to the potential of lower emissions and significant domestic reserves. These emissions can be further diminished by using noble gases, such as argon, instead of nitrogen as the working fluid in internal combustion engines. Furthermore, the use of argon as the working fluid can increase the thermodynamic efficiency due to its higher specific heat ratio. In comparison with premixed operation, the direct injection of natural gas enables the engine to reach higher compression ratios while avoiding knock. Using argon as the working fluid increases the in-cylinder temperature at top dead center (TDC) and enables the compression ignition (CI) of natural gas. In this numerical study, the combustion quality and ignition behavior of methane injected into a mixture of oxygen and argon have been investigated using a three-dimensional transient model of a constant volume combustion chamber (CVCC). A dynamic structure large eddy simulation (LES) model has been utilized to capture the behavior of the nonpremixed turbulent gaseous jet. A reduced mechanism consists of 22-species, and 104-reactions were coupled with the CFD solver. The simulation results show that the methane jet ignites at engine-relevant conditions when nitrogen is replaced by argon as the working fluid. Ignition delay times are compared across a variety of operating conditions to show how mixing affects jet development and flame characteristics.

An advanced numerical framework to model CO 2 compressors over a wide range of subcritical conditions is presented in this paper. Thermodynamic and transport properties are obtained through a table look-up procedure with specialized features for subcritical conditions. Phase change is triggered by the difference between the local values of pressure and saturation pressure, and both vaporization and condensation can be modeled. Rigorous validation of the framework is presented for condensation in high pressure CO 2 using test data in a De Laval nozzle. The comparisons between computations and test data include: condensation onset locations, Wilson line, and nozzle pressure profiles as a function of inlet pressures. The framework is applied to the Sandia compressor that has been modeled over broad range of conditions spanning the saturation dome including: near critical inlet conditions (305.4 K, and 7.843 MPa), pure liquid inlet conditions (at 295 K), pure vapor inlet conditions (at 302 K), and two-phase inlet conditions (at 290 K). Multiphase effects ranging from cavitation at the liquid line to condensation at the vapor line have been simulated. The role of real fluid effects in enhancing multiphase effects at elevated temperatures closer to the critical point has been identified. The performance of the compressor has been compared with test data; the computational fluid dynamics (CFD) results also show that the head-flow coefficient curve collapses with relatively minor scatter, similar to the test data, when the flow coefficient is defined on the impeller exit meridional velocity.