bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equivalent Circuits for the Numerical Solution of the Critical Speeds of Flexible Shafts
Authors: Kron Gabriel 
Published: March 2021

Abstract
A special type of equivalent circuit is developed that is particularly suited for the numerical calculation of the critical speeds of uniformly rotating shafts. The shaft may consist of several spans rotating in flexible bearings supported by a flexible foundation. Either the various spans may be asymmetrical along two principal axes or the bearings may have asymmetrical flexibilities. The same circuits are, of course, valid also for the study of the natural frequency of vibration of a skewed asymmetrical beam held by flexible supports at several points, such as a turbine bucket. The circuits may be solved by slide rule, by punch-card methods, or by a “network analyzer.” The procedure is self-checking as the correctness of the numbers may be checked at any stage of the calculations. For the symmetrical case, the results are identical with those found by the method of Prohl (1) or Myklestad (2), even though the circuit method requires fewer calculations. In general, the equivalent circuits for the various spans, bearings, overhung loads, and foundations are independent and are interchangeable for different combinations of shaft structure. Also, any variation in a component part leaves the circuits of the other parts unchanged. A punch-card study of a turbine generator shaft with fixed bearings carrying a high-pressure turbine, a low-pressure turbine, and a generator is given in a companion paper by A. W. Rankin (3).
Local Stress Distribution in Cylindrical Shells
Authors: Beskin Leon 
Published: March 2021

Abstract
The stress distribution in cylindrical shells with light frames is very different from the conventional beam distribution in the neighborhood of the applied loads. The problem is examined hereafter for circular cylinders with circular frames of constant section. The case of an indefinite shell with one loaded frame is examined in detail, and diagrams are given for the following unit conditions: Concentrated radial force, tangential force, couple.
A Photoelectric Method of Measuring Damping in Metal Forks at Elevated Temperatures
Authors: Pochapsky T. E. , Mase W. J. 
Published: March 2021

Abstract
Engineering measurements of internal friction in metals have been obtained from the decay characteristics of tuning forks of metals of interest. A damping program at Battelle Memorial Institute, conducted for the Office of Scientific Research and Development, called for such measurements at temperatures up to 1500 F, and it was necessary to develop suitable apparatus for obtaining accurate results at those elevated temperatures. A photoelectric method of measuring tine amplitude decay, using shutters on a vibrating fork to modulate light directed at a photocell, was developed. It proved to give very satisfactory results and had none of the mechanical difficulties in operation and uncertainties in results that were encountered at high temperatures when platinum-wire Sauereisen-cemented strain gages were used. It was necessary to reduce energy losses from the fork to its support by using a compliant coupling. This suspension worked so well that the lower limit of decrement measurements was probably determined by acoustic losses. It is believed that such losses added less than 0.00004 to the decrements of steel forks. This report includes details of construction of the equipment and reviews tests performed to establish its accuracy.
Concentrated-Force Problems in Plane Strain, Plane Stress, and Transverse Bending of Plates
Authors: Symonds P. S. 
Published: March 2021

Abstract
A general method is described for the solution of problems of transverse bending of thin plates acted on by concentrated normal forces, and of problems of plane stress or plane strain, in which concentrated forces are applied to the boundaries. The solution is taken in two parts: (a) The special functions which give the stresses or deflections in the neighborhood of the concentrated forces. (b) A complementary function, satisfying the appropriate biharmonic equation, such that the complete solution satisfies the boundary conditions of the problem. For certain types of boundaries, this complementary function can be determined by expanding the concentrated-force functions as infinite trigonometric series. Then by addition of general solutions of the appropriate biharmonic equation, the required boundary conditions may be satisfied. The method is first illustrated by solving the plate-bending problem, for which the solution is known, of a clamped circular disk loaded by a transverse force at any point. It is then applied to the problem of an infinite plate fixed at an inner circular boundary, with outer edge free, and loaded by a transverse force at any point. This solution is obtained in finite form, and typical curves of deflection, bending moments, and shear forces are given in Figs. 3 to 8, inclusive. Using this result, solutions are next obtained for ring-shaped plates of finite outer radius, with the force applied either at the outer edge or at any point between the inner clamped edge and the outer free edge. The former case was previously solved by H. Reissner. Curves comparing the maximum moments and shears in the infinite plate with those of the annular plate with force either at the outer edge, or inside the ring are given in Figs. 9 to 12, inclusive. Finally, a solution is given of the problem in plane stress of a large plate containing an elliptical hole, which is loaded by line forces at the ends of the minor axes of the ellipse. Curves showing results of this solution are given in Figs. 14 and 15.
The Influence of Oil-Film Journal Bearings on the Stability of Rotating Machines
Authors: Hagg A. C. 
Published: March 2021

Abstract
The self-excited vibration caused by the lubricating films of journal bearings and commonly called oil-film whirl or oil whip is discussed. The upper limit of whirling frequency has been found to be one-half rotational frequency in the general case; actually the phenomenon will manifest itself at a frequency which is invariably below this limit. Stability criteria have been developed for certain common systems in terms of bearing and rotor parameters. The tilting-pad bearing of Michell has been established as a so-called “stable” or “nonwhirling” bearing. This bearing and related types are probably the only oil-film journal bearings which are incapable of exciting oil whip, regardless of the system to which they are applied. Qualitatively the results of the paper appear to be in agreement with observations. In certain cases, results have been substantiated experimentally.
Analytical Design of Centrifugal Air Compressors
Authors: Concordia C. , Dowell M. F. 
Published: March 2021

Abstract
The object of this paper is to describe a general method of design and analysis which has been developed for, and applied primarily to, the design of supercharger centrifugal impellers. The method has also been used as a systematic means for the analysis of such impellers as well as for the design of the corresponding diffusers and of gas-turbine compressors and turbines. The development was undertaken with the idea of obtaining, as nearly as possible, a self-sufficient and self-contained rational design method which would be influenced as little as possible by preconceived notions of what the impeller blades should look like. The method is also complete in the sense that it is not used merely as a guide to the character of the blade shape, e.g., to determine limiting curvatures. Instead, one starts from and uses the basic laws of the fluid motion to determine the required flow path and thus the complete blade shape. On the other hand, the fullest use has been made of available experience and test results as checks of the theory.
An Improved Fuse Escapement for the Mark 18 and Other U. S. Navy Mechanical Time Fuses
Authors: Kelly F. G. , Zar J. L. 
Published: March 2021

Abstract
Theoretical shortcomings of previous Army and Navy fuse escapements are pointed out. The development of a new escape wheel and lever is described, in which spurious torques due to the fall of escape-wheel teeth against the pallets are eliminated; and a tooth shape is derived which delivers accelerating impulses symmetrically about the neutral position of the lever. Fuses with the new escapement have a timing rate which is independent of driving torque over the range of torques encountered; they can be assembled with one size of wheel and lever and with no hand-matching, function at low driving torques, and have given improved firing-test performance.
The Theory of Curved Beams
Authors: Best G. C. 
Published: March 2021

Abstract
In this paper, the theory of curved beams is developed by a somewhat different procedure from that customarily employed. Deflections at the centroid are first assumed and then loads and stresses resulting from these deflections are estimated. This process works out in a somewhat more orderly fashion than the conventional development. Throughout, all measurements are to the centroidal axis rather than to the neutral axis. Final results are presented in such a form that satisfactory accuracy may be obtained from slide-rule computations and approximate integration. Hence the procedure is applicable to any section, it being unnecessary first to develop a special formula for each different section. An illustrative example is given. The theory is extended to cover the case of unsymmetrical bending of curved beams. The effects of torsion, which will probably also occur in the generalized case, are not treated. These can be superimposed upon stresses due to bending.
Reconstructing Compressor Nonuniform Circumferential Flow Field From Spatially Undersampled Data—Part 2: Practical Application for Experiments
Authors: Lou Fangyuan , Matthews Douglas R. , Kormanik Nicholas J. , Key Nicole L. 
Published: March 2021

Abstract
In the previous part of the paper, a novel method to reconstruct the compressor nonuniform circumferential flow field using spatially undersampled data points is developed. In this part of the paper, the method is applied to two compressor research articles to further demonstrate the potential of the novel method in resolving the important flow features associated with these circumferential nonuniformities. In the first experiment, the static pressure field at the leading edge of a vaned diffuser in a high-speed centrifugal compressor is reconstructed using pressure readings from nine static pressure taps placed on the hub of the diffuser. The magnitude and phase information for the first three dominant wavelets are characterized. Additionally, the method shows significant advantages over the traditional averaging methods for calculating repeatable mean values of the static pressure. While using the multi-wavelet approximation method, the errors in the mean static pressure with one dropout measurement are 70% less than the pitchwise-averaging method. In the second experiment, the full annulus total pressure field downstream of Stator 2 in a three-stage axial compressor is reconstructed from a small segment of data representing 20% coverage of the annulus. Results show very good agreement between the reconstructed total pressure profile and the experiment at a variety of spanwise locations from near hub to near shroud. The features associated with blade row interactions accounting for passage-to-passage variations are resolved in the reconstructed total pressure profile.
Steady and Unsteady Temperature Measurements in the Wake of a Linear Cascade With Heated Airfoils
Authors: Aberle-Kern Svenja , Ripplinger Thomas , Niehuis Reinhard 
Published: March 2021

Abstract
Understanding basic aerodynamic and thermodynamic processes in engine components is critical to achieving higher efficiencies and lower fuel consumption in aircraft engines. To aid in this process, a linear compressor cascade was investigated in the high-speed cascade wind tunnel of the Institute of Jet Propulsion to quantify the influence of heat transfer on the temperature distribution in the wake and, finally, the profile loss. For this purpose, a patented five-hole probe with an integrated thermocouple was developed and applied for steady measurements. Additionally, a hot-wire measurement setup was implemented to receive temperature fluctuations via the constant current (CC) mode as well as velocity fluctuations via the constant temperature (CT) mode. A novel method for a two-way temperature and velocity correction for the two types of hot-wire measurement is presented. Good agreement between the measurement data of the five-hole probe and averaged data from hot-wire anemometry was found. The temperature distribution indicates the occurrence of energy separation which in some cases is overlain with the effects of heat transfer. In addition, the analysis of unsteady fluctuations of temperature and velocity give more detailed information about the vortex shedding in the wake, including the size of the vortices. Finally, this is the first discussion of energy separation at a compressor cascade combined with overlain effects of heat transfer on the blade surface.
A Machine-Learnt Wall Function for Rotating Diffusers
Authors: Tieghi Lorenzo , Corsini Alessandro , Delibra Giovanni , Tucci Francesco Aldo 
Published: March 2021

Abstract
Data-driven tools and techniques have proved their effectiveness in many engineering applications. Machine-learning has gradually become a paradigm to explore innovative designs in turbomachinery. However, industrial computational fluid dynamics (CFD) experts are still reluctant to embed similar approaches in standard practice and very few solutions have been proposed so far. The aim of the work is to prove that standard wall treatments can obtain serious benefits from machine-learning modeling. Turbomachinery flow modeling lives in a constant compromise between accuracy and the computational costs of numerical simulations. One of the key factors of the process is defining a proper wall treatment. Many works point out how insufficient resolutions of boundary layers may lead to incorrect predictions of turbomachinery performances. Wall functions are universally exploited to replicate the physics of boundary layers where grid resolution does not suffice. Widespread wall functions were derived by the observation of a few canonical flows, further expressed as a simple polynomial of Reynolds number and turbulent kinetic energy. Despite their popularity, these functions are frequently applied in flows where the ground assumptions cease to be true, such as rotating passages or swirled flows. In these flows, the mathematical formulations of wall functions do not account for the distortion on the boundary layer due to the combined action of centrifugal and Coriolis forces. Here, we will derive a wall function for rotating passages, through means of machine-learning. The algorithm is directly implemented in the NS equations solver. Cross-validation results show that the machine-learnt wall treatment is able to effectively correct the turbulent kinetic energy field near the solid walls, without impairing the accuracy of the Reynolds-averaged numerical simulations (RANS) turbulence model in any way.
Experimental Investigation of Tip Design Effects on the Unsteady Aerodynamics and Heat Transfer of a High-Speed Turbine
Authors: Cernat Bogdan C. , Lavagnoli Sergio 
Published: March 2021

Abstract
While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high-pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. In the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. Reynolds-averaged Navier–Stokes (RANS) simulations are employed to predict the aerodynamic and thermal fields of the individual profiles using test-calibrated boundary conditions. Isothermal steady computations are performed at different wall temperatures to compute the adiabatic wall temperature and the heat transfer convective coefficient. Low-order models are used to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high-frequency aerodynamic measurements to identify the rotor secondary flow structures.
Single and Multiple Circumferential Casing Groove for Stall Margin Improvement in a Transonic Axial Compressor
Authors: Mustaffa A. F. , Kanjirakkad V. 
Published: March 2021

Abstract
The stability limit of a tip-stalling axial compressor is sensitive to the magnitude of the near-casing blockage. In transonic compressors, the presence of the passage shock could be a major cause for the blockage. Identification and elimination of this blockage could be a key to improving the stability limit of the compressor. In this article, using numerical simulation, the near-casing blockage within the transonic rotor, NASA Rotor 37, is quantified using a blockage parameter. For a smooth casing, the blockage at conditions near stall is maximum at about 20% of the tip axial chord downstream of the tip leading edge. This maximum blockage location is found to be consistent with the location of the passage shock–tip leakage vortex interaction. A datum single casing groove design that minimizes the peak blockage is found through an optimization approach. The stall margin improvement of the datum casing groove is about 0.6% with a negligible efficiency penalty. Furthermore, the location of the casing groove is varied upstream and downstream of the datum location. It is shown that the stability limit of the compressor is best improved when the blockage is reduced upstream of the peak blockage location. This article also discusses the prospects of a multigroove casing configuration.
Detailed Experimental Study of the Flow in a Turbine Rear Structure at Engine-Realistic Flow Conditions
Authors: Vikhorev Valentin , Chernoray Valery , Thulin Oskar , Deshpande Srikanth , Larsson Jonas 
Published: March 2021

AbstractA good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency and reducing emissions from aero-engines. This paper presents a detailed experimental evaluation of an engine-realistic TRS which was studied in an engine-realistic rig at Chalmers University of Technology, Sweden. The TRS test section was equipped with three types of outlet guide vanes (OGVs) which are typical of modern state-of-the-art TRS: regular vanes, thickened vanes, and vanes with an engine-mount recess (a shroud bump). Each of the three vane geometries was studied under on-design and off-design conditions at a fixed flow Reynolds number of 235,000. The study shows that the off-design performance of the TRS strongly depends on the presence of the local flow separation on the OGV suction side near the hub, which is greatly affected by the vane pressure distribution and inlet conditions. Similarly, the OGVs with increased thickness and with a vane shroud bump are shown to affect the performance of the TRS by influencing the losses on the OGV suction side near the hub. Furthermore, the presence of the bump is shown to have a noticeable upstream influence on the outlet flow from the low-pressure turbine and a noticeable downstream influence on the outlet flow from the TRS.
Uncertainty Evaluation on Multi-Hole Aerodynamic Pressure Probes
Authors: Notaristefano Andrea , Gaetani Paolo , Dossena Vincenzo , Fusetti Alberto 
Published: March 2021

Abstract
In the frame of a continuous improvement of the performance and accuracy in the experimental testing of turbomachines, the uncertainty analysis on measurements instrumentation and techniques is of paramount importance. For this reason, since the beginning of the experimental activities at the Laboratory of Fluid Machines (LFM) located at Politecnico di Milano (Italy), this issue has been addressed and different methodologies have been applied. This paper proposes a comparison of the results collected applying two methods for the measurement uncertainty quantification to two different aerodynamic pressure probes: sensor calibration, aerodynamic calibration and probe application are considered. The first uncertainty evaluation method is the so-called “uncertainty propagation” method (UPM); the second is based on the “Monte Carlo” method (MCM). Two miniaturized pressure probes have been selected for this investigation: a pneumatic five-hole probe and a spherical fast-response aerodynamic pressure probe (sFRAPP), the latter applied as a virtual four-hole probe. Since the sFRAPP is equipped with two miniaturized pressure transducers installed inside the probe head, a specific calibration procedure and a dedicated uncertainty analysis are required.
High-Fidelity Simulations of a High-Pressure Turbine Vane Subject to Large Disturbances: Effect of Exit Mach Number on Losses
Authors: Zhao Yaomin , Sandberg Richard D. 
Published: March 2021

Abstract
We report on a series of highly resolved large-eddy simulations of the LS89 high-pressure turbine (HPT) vane, varying the exit Mach number between Ma = 0.7 and 1.1. In order to accurately resolve the blade boundary layers and enforce pitchwise periodicity, we for the first time use an overset mesh method, which consists of an O-type grid around the blade overlapping with a background H-type grid. The simulations were conducted either with a synthetic inlet turbulence condition or including upstream bars. A quantitative comparison shows that the computationally more efficient synthetic method is able to reproduce the turbulence characteristics of the upstream bars. We further perform a detailed analysis of the flow fields, showing that the varying exit Mach number significantly changes the turbine efficiency by affecting the suction-side transition, blade boundary layer profiles, and wake mixing. In particular, the Ma = 1.1 case includes a strong shock that interacts with the trailing edge, causing an increased complexity of the flow field. We use our recently developed entropy loss analysis (Zhao and Sandberg, 2019, “Using a New Entropy Loss Analysis to Assess the Accuracy of RANS Predictions of an HPT Vane,” ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, Paper No. GT2019-90126) to decompose the overall loss into different source terms and identify the regions that dominate the loss generation. Comparing the different Ma cases, we conclude that the main mechanism for the extra loss generation in the Ma = 1.1 case is the shock-related strong pressure gradient interacting with the turbulent boundary layer and the wake, resulting in significant turbulence production and extensive viscous dissipation.