Results for “Conditional Normalizing Flow” — Page 12

DOE OSTI2022

UK-US Collaboration on Fossil Energy R&D: Steam Side Oxidation

In recent years, interest in increasing the efficiency of power plants based on steam generation has led to the need to develop and qualify materials capable of operating at steam temperatures and pressures significantly higher than those employed in current power plants. The overall focus of this international program is on using ferritic-martensitic steels to the maximum possible temperature, before switching to austenitic steels and/or Ni-based alloys. The relatively low Cr content of these alloys raises concerns regarding their resistance to steam oxidation at these higher temperatures. Earlier work in this collaboration addressed the reliability of data from atmospheric pressure, laboratory-based steam oxidation tests. This raised issues regarding how representative the laboratory-grown oxides were compared to those formed on service-exposed material and how the tests could be made more reliable by introducing added complexity. In general laboratory-scale exposures are conducted under isothermal conditions at ambient or slightly elevated pressure, using a relatively low flow rate of steam. The coupons used in these tests are normally flat cuboids which have been ground to homogenise the surface and remove any pre-existing features. However, there is a concern that these samples and exposures are not representative of service conditions, and so it is necessary to quantify the influence of transient conditions, such as heat flux, pressure and sample geometry/surface conditions. To address such concerns a new collaborative program of work was initiated to determine the influence of these added features on oxidation kinetics and oxide scale morphology. The overall aim was to improve the understanding of alloy performance in ultrasupercritical (USC) steam conditions and qualify suitable test procedures.

20 FOSSIL-FUELED POWER PLANTS↗

NASA NTRS2018

Integrated Oxygen Flow Meter/Heat Exchanger for Portable Life Support Systems

Space suits for future exploration missions will have multi-mission goals with new and challenging requirements for the portable life support system (PLSS). In particular, the space suit ventilation loop requires cooling and flow measurement components that must meet specifications that go well beyond the capabilities of the components used for the existing Extravehicular Mobility Unit. The flow meter must have high measurement accuracy over a wide flow range, compatibility with pure oxygen, low pressure losses, and very compact size. The heat exchanger that cools the ventilation loop must be built from materials that are compatible with the liquid cooling loop, and it must provide efficient gas cooling in a small package across conditions ranging from normal suit pressure to elevated pressure. This paper describes the development of a novel device that combines the flow measurement and cooling functions in a single, compact flow meter/heat exchanger (FMHX). We have developed design methods that enable us to assess trade-offs, optimize performance, and specify the design of an FMHX that meets the requirements and constraints for operation in future PLSSs. We used empirical design correlations combined with computational fluid dynamics analysis to design the FMHX design. Data from tests of a proof-of-concept FMHX validate the design methods and show that the device meets all design requirements. We used the results from these tests to refine the design parameters and predict performance of an optimized, prototype FMHX.

Izenson, Michael G.↗

NASA NTRS2004

Increasing Accuracy in Computed Inviscid Boundary Conditions

A technique has been devised to increase the accuracy of computational simulations of flows of inviscid fluids by increasing the accuracy with which surface boundary conditions are represented. This technique is expected to be especially beneficial for computational aeroacoustics, wherein it enables proper accounting, not only for acoustic waves, but also for vorticity and entropy waves, at surfaces. Heretofore, inviscid nonlinear surface boundary conditions have been limited to third-order accuracy in time for stationary surfaces and to first-order accuracy in time for moving surfaces. For steady-state calculations, it may be possible to achieve higher accuracy in space, but high accuracy in time is needed for efficient simulation of multiscale unsteady flow phenomena. The present technique is the first surface treatment that provides the needed high accuracy through proper accounting of higher-order time derivatives. The present technique is founded on a method known in art as the Hermitian modified solution approximation (MESA) scheme. This is because high time accuracy at a surface depends upon, among other things, correction of the spatial cross-derivatives of flow variables, and many of these cross-derivatives are included explicitly on the computational grid in the MESA scheme. (Alternatively, a related method other than the MESA scheme could be used, as long as the method involves consistent application of the effects of the cross-derivatives.) While the mathematical derivation of the present technique is too lengthy and complex to fit within the space available for this article, the technique itself can be characterized in relatively simple terms: The technique involves correction of surface-normal spatial pressure derivatives at a boundary surface to satisfy the governing equations and the boundary conditions and thereby achieve arbitrarily high orders of time accuracy in special cases. The boundary conditions can now include a potentially infinite number of time derivatives of surface-normal velocity (consistent with no flow through the boundary) up to arbitrarily high order. The corrections for the first-order spatial derivatives of pressure are calculated by use of the first-order time derivative velocity. The corrected first-order spatial derivatives are used to calculate the second- order time derivatives of velocity, which, in turn, are used to calculate the corrections for the second-order pressure derivatives. The process as described is repeated, progressing through increasing orders of derivatives, until the desired accuracy is attained.

Dyson, Roger↗

NASA NTRS1999

Measurement of Two-Phase Flow Characteristics Under Microgravity Conditions

This paper describes the technical approach and initial results of a test program for studying two-phase annular flow under the simulated microgravity conditions of KC-135 aircraft flights. A helical coil flow channel orientation was utilized in order to circumvent the restrictions normally associated with drop tower or aircraft flight tests with respect to two-phase flow, namely spatial restrictions preventing channel lengths of sufficient size to accurately measure pressure drops. Additionally, the helical coil geometry is of interest in itself, considering that operating in a microgravity environment vastly simplifies the two-phase flows occurring in coiled flow channels under 1-g conditions for virtually any orientation. Pressure drop measurements were made across four stainless steel coil test sections, having a range of inside tube diameters (0.95 to 1.9 cm), coil diameters (25 - 50 cm), and length-to-diameter ratios (380 - 720). High-speed video photographic flow observations were made in the transparent straight sections immediately preceding and following the coil test sections. A transparent coil of tygon tubing of 1.9 cm inside diameter was also used to obtain flow visualization information within the coil itself. Initial test data has been obtained from one set of KC-135 flight tests, along with benchmark ground tests. Preliminary results appear to indicate that accurate pressure drop data is obtainable using a helical coil geometry that may be related to straight channel flow behavior. Also, video photographic results appear to indicate that the observed slug-annular flow regime transitions agree quite reasonably with the Dukler microgravity map.

Keshock, E. G.↗

NASA NTRS1974

Shock shapes of blunt bodies in hypersonic helium, air, and CO2 flows

A primary factor governing hypersonic flowfield characteristics of blunt vehicles entering planetary atmospheres is the normal shock density ratio. Hence, a means of duplicating or simulating the high density ratios experienced during planetary entry is needed. One facility having the capability of generating a range of hypersonic-hypervelocity flow conditions in arbitrary test gases is the expansion tube. Preliminary shock shape results obtained in the Langley 6-in. expansion tube at hypersonic conditions are presented. Normal shock density ratios from approximately 4 to 19 were generated using helium, air, and CO2 test gases at freestream velocities from 5 to 7 km/sec. Test models were a flat-faced cylinder and the Viking aeroshell.

Miller, C. G.↗

NASA NTRS1999

Influence of Buoyant Convection on the Stability of Enclosed Laminar Flames

An investigation of the stability limits of Enclosed Laminar Flames (ELF) was conducted in the Middeck Glovebox (MGBX) facility on the STS-87 Space Shuttle mission (November to December 1997). The primary objective of the ELF glovebox investigation is to determine the effect of buoyancy on the stability of round, laminar, gas-jet diffusion flames in a co-flow air duct. Comparison tests were conducted in normal gravity to allow isolation and identification of the influence of buoyancy. The results were used to map the lift-off and blow-out stability limits as a function of the fuel and air velocities for the two buoyancy conditions. Approximately 50 tests were conducted during the Space Shuttle mission, using a 50/50 mixture (volume basis) of methane and nitrogen as the fuel. The experimental results verified the hypothesis that substantially greater velocities are required to destabilize the flame in microgravity. The increase in air velocity required to induce lift off in microgravity (compared to normal gravity) was nearly equal to the increase required to induce blow out. Furthermore, the air velocity increase was relatively independent of the fuel flow, except at low fuel flows. At high fuel flows, it was found that the microgravity flames tend to immediately blow out after lift off. This is in agreement with the free-jet theory which suggests that stable lifted flames are not possible for fuels with a Schmidt number of 0.5<Sc<l, such as the diluted methane used in this study. However, stable lifted flames were observed in microgravity at low fuel flows, and in normal gravity, despite the fuel's low Schmidt number. The discrepancy between the experimental data and the theory of Chung and Lee is presumably due to the differences in the flow condition; namely, the ducted flow versus a free jet, and a non-similar velocity profile versus a self-similar profile.

Brooker, John E.↗

DOE OSTI2023

Demonstration of Pronghorn’s Subchannel Code Modeling of Liquid-Metal Reactors and Validation in Normal Operation Conditions and Blockage Scenarios

Pronghorn-SC is a subchannel code within the Multiphysics Object-Oriented Simulation Environment (MOOSE). Initially designed to simulate flows in water-cooled, square lattice, subchannel assemblies, Pronghorn-SC has been expanded to simulate liquid-metal-cooled flows in triangular lattices, hexagonal subchannel assemblies. For this purpose, the algorithm of Pronghorn-SC was adapted to solve the subchannel equations as they are applicable to a hexagonal wire-wrapped sodium-cooled fast reactor. Cheng–Todreas models for pressure drop and cross-flow models were adopted and a coolant heat conduction term was added. To solve these equations, an improved implicit algorithm was developed robust enough to deal with the numerical issues, associated with low flow and recirculation phenomena. To confirm the prediction capability of Pronghorn-SC, calculations and comparisons with available experimental data of 19- and 37-pin assemblies were performed, as well as other subchannel codes. Finally, a flow blockage modeling feature was added. This capability was validated for both water-cooled square sub-assemblies and sodium-cooled hexagonal sub-assemblies, using experimental data of partially and fully blocked cases.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS2009

Visco Jet Joule-Thomson Device Characterization Tests in Liquid Methane

Joule-Thomson (J-T) devices have been identified as critical components for Thermodynamic Vent Systems (TVS) planned for future space exploration missions. Lee Visco Jets (The Lee Company) (Ref. 4) are one type of J-T device that may be used for LCH4 propellant systems. Visco Jets have been previously tested and characterized in LN2 and LH2 (Refs. 6 and 7), but have not been characterized in LOX or LCH4. Previous Visco Jet tests with LH2 resulted in clogging of the Visco Jet orifice under certain conditions. It has been postulated that this clogging was due to the presence of neon impurities in the LH2 that solidified in the orifices. Visco Jets therefore require testing in LCH4 to verify that they will not clog under normal operating conditions. This report describes a series of tests that were performed at the NASA Glenn Research Center to determine if Visco Jets would clog under normal operating conditions with LCH4 propellant. Test results from this program indicate that no decrease in flow rate was observed for the Visco Jets tested, and that current equation used for predicting flow rate appears to under-predict actual flow at high Lohm ratings.

Jurns, John M.↗

NASA NTRS2016

Passive Rocket Diffuser Testing: Reacting Flow Performance of Four Second-Throat Geometries

Second-throat diffusers serve to isolate rocket engines from the effects of ambient back pressure. As one of the nation's largest rocket testing facilities, the performance and design limitations of diffusers are of great interest to NASA's Stennis Space Center. This paper describes a series of tests conducted on four diffuser configurations to better understand the effects of inlet geometry and throat area on starting behavior and boundary layer separation. The diffusers were tested for a duration of five seconds with a 1455-pound thrust, LO2/GH2 thruster to ensure they each reached aerodynamic steady state. The effects of a water spray ring at the diffuser exits and a water-cooled deflector plate were also evaluated. Static pressure and temperature measurements were taken at multiple axial locations along the diffusers, and Computational Fluid Dynamics (CFD) simulations were used as a tool to aid in the interpretation of data. The hot combustion products were confirmed to enable the diffuser start condition with tighter second throats than predicted by historical cold-flow data or the theoretical normal shock method. Both aerodynamic performance and heat transfer were found to increase with smaller diffuser throats. Spray ring and deflector cooling water had negligible impacts on diffuser boundary layer separation. CFD was found to accurately capture diffuser shock structures and full-flowing diffuser wall pressures, and the qualitative behavior of heat transfer. However, the ability to predict boundary layer separated flows was not consistent.

Jones, Daniel R.↗

NASA NTRS1984

Effect of initial conditions on turbulent reattachment downstream of a backward-facing step

The reattachment of a fully turbulent, two-dimentional shear layer downstream of a backward-facing step has been studied experimentally. The work examines the effect of variations in inlet conditions on the process of reattachment. A series of experiments was conducted in a low-speed wind tunnel using specialized instrumentation suited to the highly turbulent reversing flow near reattachment. Accurate characterization of the time-mean features of the reattaching flows was possible. Assuming linear scaling normalized on distance from reattachment, distributions of normalized pressure coefficient and forward flow fraction, and time-averaged skin friction coefficient appear universal for two-dimensional reattachment, independent of initial conditions and step height, for given duct geometry (area ratio) and for high step-height Reyolds numbers with thin separating boundary layers. The results suggest universal flow structure in the reattachment zone.

Westphal, R. V.↗

DOE OSTI2024

MARVEL Reactor Fuel Performance Report (Rev.2)

The Microreactor Applications Research Validation and EvaLuation (MARVEL) project is producing a high temperature liquid metal-cooled nuclear test bed at Idaho National Laboratory (INL) to ultimately improve the integration of microreactors to end-user applications. This ambitious effort seeks to design, authorize, construct, test, and operate the reactor within five years. In order to construct and operate the MARVEL reactor in a timely manner, the system will utilize materials and component designs which have already been used, qualified, or licensed from previous reactors. The MARVEL reactor will be located at the INL Transient Reactor Test (TREAT) facility in the north high-bay equipment pit and will use the existing 304 stainless steel-clad U-ZrH1.6 pin-type fuel system developed by General Atomics and purchased from TRIGA International. This fuel has been previously qualified under the United States Department of Energy’s (US DOE) Reduced Enrichment for Research and Test Reactors (RERTR) Program. Even though the regulator of the MARVEL reactor is the US DOE, the standards and overall approach recommended by the Nuclear Regulatory Commission is well-defined and utilized here. Following NUREG-1537 regulatory guidance, this report documents the authorization case for the MARVEL fuel system’s application to MARVEL and establishes stable and predictable fuel performance during the most thermophysically unfavorable conditions achievable in the MARVEL reactor. To that end, this report provides a comprehensive survey of the known thermophysical properties, performance, and quantitative relationships associated with the MARVEL reactor fuel element and uses this information to determine its mechanical integrity and risk of reaching unacceptable conditions during the most extreme accident scenarios predicted for the reactor using the most conservative assumptions available. The information contained herein is compiled from a combination of historical reports and peer reviewed scientific publication manuscripts. Known mechanisms under which the fuel is susceptible to failure are highlighted and compared to conditions that could exist in the MARVEL reactor during an unanticipated transient or accident scenario. The two scenarios considered for analysis in this report are (1) an unprotected loss of flow accident and (2) a hypothetical unprotected loss of coolant accident during the loss of flow accident. Preliminary 2D steady-state analyses herein indicate that both fuel-cladding chemical interactions and fuel-cladding mechanical interactions are negligible throughout the fuel’s operational cycle under both normal and high temperature accident scenario conditions. Although higher fidelity 3D time-dependent modeling and simulations are planned, the following may be concluded presently. The MARVEL fuel element maintains its geometric stability and structural integrity during the most extreme accident scenarios predicted for the MARVEL reactor. The hoop stress during the unprotected loss of flow accident reaches about -1.27 MPa; this negative stress indicates that it is compressive rather than tensile. The compressive stress is a result of the NaK pressure on the outside of the fuel element, caused by the restricted thermal expansion of the NaK coolant, exceeding the internal pressures generated inside of the fuel element. The hoop stress generated in the cladding during the unprotected loss of coolant accident reaches a maximum of about approximately 10 MPa, which is nearly an order of magnitude less than the predicted yield strength of the cladding under high-temperature accident scenario conditions. Calculations were compared with results from high performance computational simulations using BISON and are in very close agreement. A conservative MARVEL fuel meat peak temperature limit of 900 °C is recommended presently, which is about 180 °C higher than the peak fuel temperature predicted to occur during the most extreme accident. Based on the known properties and behavior of the MARVEL fuel element, the fuel successfully meets its design and safety requirements under normal and most extreme accident conditions with a large safety margin.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2026

MARVEL Reactor Fuel Performance Report

The Microreactor Applications Research Validation and EvaLuation (MARVEL) project is producing a high temperature liquid metal-cooled nuclear test bed at Idaho National Laboratory (INL) to ultimately improve the integration of microreactors to end-user applications. This ambitious effort seeks to design, authorize, construct, test, and operate the reactor within five years. In order to construct and operate the MARVEL reactor in a timely manner, the system will utilize materials and component designs which have already been used, qualified, or licensed from previous reactors. The MARVEL reactor will be located at the INL Transient Reactor Test (TREAT) facility in the north high-bay equipment pit and will use the existing 304 stainless steel-clad U-ZrH1.6 pin-type fuel system developed by General Atomics and purchased from TRIGA International. This fuel has been previously qualified under the United States Department of Energy’s (US DOE) Reduced Enrichment for Research and Test Reactors (RERTR) Program. Even though the regulator of the MARVEL reactor is the US DOE, the standards and overall approach recommended by the Nuclear Regulatory Commission is well-defined and utilized here. Following NUREG-1537 regulatory guidance, this report documents the authorization case for the MARVEL fuel system’s application to MARVEL and establishes stable and predictable fuel performance during the most thermophysically unfavorable conditions achievable in the MARVEL reactor. To that end, this report provides a comprehensive survey of the known thermophysical properties, performance, and quantitative relationships associated with the MARVEL reactor fuel element and uses this information to determine its mechanical integrity and risk of reaching unacceptable conditions during the most extreme accident scenarios predicted for the reactor using the most conservative assumptions available. The information contained herein is compiled from a combination of historical reports and peer reviewed scientific publication manuscripts. Known mechanisms under which the fuel is susceptible to failure are highlighted and compared to conditions that could exist in the MARVEL reactor during an unanticipated transient or accident scenario. The two scenarios considered for analysis in this report are (1) an unprotected loss of flow accident and (2) a hypothetical unprotected loss of coolant accident during the loss of flow accident. Preliminary 2D steady-state analyses herein indicate that both fuel-cladding chemical interactions and fuel-cladding mechanical interactions are negligible throughout the fuel’s operational cycle under both normal and high temperature accident scenario conditions. Although higher fidelity 3D time-dependent modeling and simulations are planned, the following may be concluded presently. The MARVEL fuel element maintains its geometric stability and structural integrity during the most extreme accident scenarios predicted for the MARVEL reactor. The hoop stress during the unprotected loss of flow accident reaches about -1.27 MPa; this negative stress indicates that it is compressive rather than tensile. The compressive stress is a result of the NaK pressure on the outside of the fuel element, caused by the restricted thermal expansion of the NaK coolant, exceeding the internal pressures generated inside of the fuel element. The hoop stress generated in the cladding during the unprotected loss of coolant accident reaches a maximum of about approximately 10 MPa, which is nearly an order of magnitude less than the predicted yield strength of the cladding under high-temperature accident scenario conditions. Calculations were compared with results from high performance computational simulations using BISON and are in very close agreement. A conservative MARVEL fuel meat peak temperature limit of 900 °C is recommended presently, which is about 180 °C higher than the peak fuel temperature predicted to occur during the most extreme accident. Based on the known properties and behavior of the MARVEL fuel element, the fuel successfully meets its design and safety requirements under normal and most extreme accident conditions with a large safety margin.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2020

Joint Estimation of Operational Topology and Outages for Unbalanced Power Distribution Systems

Not provided.

Engineering↗

DOE OSTI2016

Study of Convection Heat Transfer in a Very High Temperature Reactor Flow Channel: Numerical and Experimental Results

Very High Temperature Reactors (VHTRs) are one of the Generation IV gas-cooled reactor models proposed for implementation in next generation nuclear power plants. A high temperature/pressure test facility for forced and natural circulation experiments has been constructed. This test facility consists of a single flow channel in a 2.7 m (9’) long graphite column equipped with four 2.3kW heaters. Extensive 3D numerical modeling provides a detailed analysis of the thermal-hydraulic behavior under steady-state, transient, and accident scenarios. In addition, forced/mixed convection experiments with air, nitrogen and helium were conducted for inlet Reynolds numbers from 500 to 70,000. Our numerical results were validated with forced convection data displaying maximum percentage errors under 15%, using commercial finite element package, COMSOL Multiphysics. Based on this agreement, important information can be extracted from the model, with regards to the modified radial velocity and property gas profiles. Our work also examines flow laminarization for a full range of Reynolds numbers including laminar, transition and turbulent flow under forced convection and its impact on heat transfer under various scenarios to examine the thermal-hydraulic phenomena that could occur during both normal operation and accident conditions.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRS1986

On a difficulty with accelerating particles at slow-mode shocks

The available information on slow-mode shocks is briefly reviewed in order to determine whether these shocks are capable of accelerating particles to high energies, thus providing a possible mechanism for energetic particle production at reconnection sites. It is noted that in contrast to fast shocks, the evolutionary conditions at a steady slow shock require the upstream plasma to flow into the shock with a normal component slower than the intermediate speed. Consequently, the right-polarized waves will escape from a slow shock, and backstreaming particles scattered by these waves will not be convected back to the shock. There will be no effective compression, and further acceleration will not occur.

Isenberg, P. A.↗

NASA NTRS2001

Membrane Separation of Gases From The Martian Atmosphere

A test bed has been constructed to test membrane modules for separation of gases under temperature and pressure conditions normally encountered on the surface of Mars. The test bed allows independent control of (1) feed flow rates, (2) feed composition, (3) feed pressure, (4) permeate pressure, and (5) operating temperature. Preliminary data obtained at a nominal feed pressure of 760 torr and permeate pressure of 10 torr has demonstrated the ability of one membrane module to operate at temperatures as low as -70 C. At temperatures below -40 C, however, significant loss of carbon dioxide and argon was observed, probably indicating condensation at the relatively high pressure used. As expected, permeation flow rates decreased with decreasing temperature, the flow at -30 C approximately 37% of the value at +23 C. Values of permeability for individual gas components showed similar decreases with decreasing temperature, but permeability ratios changed significantly. For example, the ratio of the permeabilities of carbon dioxide and nitrogen increased from 2.6 at 23 C to 5.6 at -30 C. Additional data at lower operating pressures and temperatures must be obtained in order to optimize design of a usable separation system.

Jennings, Paul A.↗

NASA NTRS2002

Membrane Separation of Gases from the Martian Atmosphere

A test bed has been constructed to test membrane modules for separation of gases under temperature and pressure conditions normally encountered on the surface of Mars. The test bed allows independent control of: (1) feed flow rates, (2) feed composition, (3) feed pressure, (4) permeate pressure, and (5) operating temperature. Preliminary data obtained at a nominal feed pressure of 760 torr and permeate pressure of 10 torr has demonstrated the ability of one membrane module to operate at temperatures as low as -70 C. At temperatures below -40 C, however, significant loss of carbon dioxide and argon was observed, probably indicating condensation at the relatively high pressure used. As expected, permeation flow rates decreased with decreasing temperature, the flow at -30 C approximately 37% of the value at +23 C. Values of permeability for individual gas components showed similar decreases with decreasing temperature, but permeability ratios changed significantly. For example, the ratio of the permeabilities of carbon dioxide and nitrogen increased from 2.6 at 23 C to 5.6 at -30 C. Additional data at lower operating pressures and temperatures must be obtained in order to optimize design of a usable separation system.

Jennings, Paul A.↗

NASA NTRS1993

Laser velocimeter measurements of the flow field generated by a forward-swept propfan during flutter

Results are presented from an investigation to measure the flow field generated by a forward-swept propfan operating in flutter at a low forward velocity. For comparison to the flutter condition, flow field data are also presented for a slightly reduced rotational speed just below flutter. The forward-swept propfan was tested as the front rotor of a counterrotating pusher propeller. A laser Doppler velocimeter (LDV) was used to measure the velocity field in planes normal to the model centerline downstream of the rotor and in planes of constant radius within the blade passages at each operating condition. A comparison of the data taken at the two different operating conditions indicated that the mean, time-averaged flow about the blades did not change drastically as the propfan rotational speed was increased from the stable operating point to the flutter condition. No regions of flow separation could be identified in the data plots of the mean intrablade flow field. The data also indicate that the relative flow about the blades remained subsonic during flutter operation. The blades were found to have a higher than expected tip loading at both operating conditions. This is thought to have been caused by the outer blade sections twisting under load to higher than expected effective blade angles. This high tip loading resulted in strong vortices and a very nonuniform flow downstream of the tips of the forward-swept blades. This high tip loading may also have caused the blade flutter.

Podboy, Gary G.↗