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At least 109 records · Page 6
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NASA NTRS2004

Single Airfoil Gust Response Problem: Category 3, Problem 1

An unsteady aerodynamic code, called GUST3D (ref. 3), has been developed to solve equation (8) for flows with periodic vortical disturbances. The code uses a frequency-domain approach with second-order central differences and a pressure radiation condition in the far field. GUST3D requires as input certain mean flow quantities which are calculated separately by a potential flow solver. The solver calculates the mean ow using a Gothert's Rule approximation (ref. 3). On the airfoil surface, it uses the solution calculated by the potential code FLO36 (ref. 4). Figures 1-2 show the mean pressure along the airfoil surface for the two airfoil geometries. In Figures 3 - 8, we present the RMS pressure on the airfoil surface. Each figure shows three GUST3D solutions (calculated on grids with different far-field boundary locations). Three solutions are shown to provide some indication of the numerical uncertainty in the results. Figures 9 - 13 present the acoustic intensity. We again show three solutions per case. Note that no results are presented for the k1 = k2 = 2.0 loaded airfoil case, as an acceptable solution could not be obtained. A few comments need to be made about the results shown. First, since the last Workshop, the GUST3D code has been substantially upgraded. This includes implementing a more accurate far-field boundary condition (ref. 5) and developing improved gridding capabilities. This is the reason for any differences that may exist between the present results and results from the last Workshop. Second, the intensity results on the circle R = 4C were obtained using a Kirchoff method (ref. 6). The Kirchoff surface was the circle R = 2C. Finally, the GUST3D code is most accurate for low reduced frequencies. A new domain decomposition approach (ref. 7) has been developed to improve accuracy. Both the single domain and domain decomposition approaches were used in generating the present results.

Scott, James R.↗
NASA NTRS2004

Benchmark Solution For The Category 3, Problem 2: Cascade - Gust Interaction

The benchmark solution for the cascade-gust interaction problem is computed using a linearized Euler code called LINFLUX. The inherently three-dimensional code is run in the thin-annulus limit to compute the two-dimensional cascade response. The calculations are carried out in the frequency-domain and the unsteady response at each of the gust s three frequency component is computed. The results are presented on modal basis for pressure perturbations (i.e., acoustic modes) as well as velocity perturbations (i.e., convected gust modes) at each frequency.

Envia, Edmane↗
NASA NTRS2004

Comparisons of the Solutions for the Category 3--Problem 2: Cascade-Gust Interaction

Six different solutions were submitted for this benchmark problem. These were obtained using a variety of methods that can be conveniently categorized in two main groups, a nonlinear time-domain group and a linearized frequency-domain group. The first includes solutions submitted by (1) Hixon, (2) Nallasamy et. al, (3) Shieh et. al, and (4) Wang et. al, and the second includes solutions submitted by (5) Coupland and (6) Serrano et. al. Methods (1) and (2) use sixth order compact differencing schemes and the rest are essentially second order in space. With the exception of the solution submitted by Shieh et. al, all are individually discussed in great detail in the workshop proceedings. Comparisons of the submitted solutions with the benchmark solution are presented below. Due to differences in the level of solution detail provided to the author by the participants, the comparisons do not always include results from all submissions. It should be noted at the outset that, since the benchmark solution itself was numerically computed, the comparisons are somewhat subjective. In order to provide maximum latitude for the participants of the workshop, no restrictions were placed on the type of method that could be used to solve the problem. Neither was there were any stipulations to use a particular grid topology or grid density. Therefore, without a detailed study of the critical features of the computed solutions, it is not possible to make concrete statements about the relative merits of one method over another. Such a study is beyond the scope of the current exercise, especially since complete flowfield details were not provided to the author by all participants. Instead a package, containing the information about the benchmark solution (both the steady and unsteady parts of it), is included on the proceedings CD should the authors who submitted solutions for this problem wish to examine in detail the benchmark solution and compare their results to it.

Envia, Edmane↗
NASA NTRS2004

Category 5: Sound Generation In Viscous Problems. Problem 2: Sound Generation By Flow Over a Cavity

The discrete frequency sound produced by the flow of air at low subsonic speeds over a deep cavity was investigated. A long aspect ratio rectangular cavity with a leading edge overhang that cut off of the cavity opening was placed flush with the top surface of a wind tunnel. The approach flow velocity was maintained at 50 m/s for the benchmark problem although results are also presented for other conditions. Boundary layer measurements conducted with a single element hotwire anemometer indicated that the boundary layer thickness just upstream of the cavity was equal to 17 mm. Sound pressure level measurements were made at three locations in the cavity: the center of the leading edge wall, the center of the cavity floor, and the center of the trailing edge wall. Three discrete tones were measured at all three locations with corresponding Strouhal numbers (based on cavity opening length and approach flow velocity) equal to 0.24, 0.26, and 0.41. The amplitudes of each tone were approximately equal at each measurement location in the cavity. Measurements made at other approach flow conditions indicated that the approach flow velocity and the boundary layer thickness affected the frequency characteristics of the discrete tones.

Henderson, Brenda S.↗
NASA NTRS2004

Category 3: Sound Generation by Interacting With a Gust

Solve the time-dependent inviscid flow equations for this geometry subject to the specified inflow/outflow mean conditions and the fluctuating inflow velocity distortion. (1) Compute the unsteady solution until periodicity in pressure is achieved by showing that at least two successive periods are identical. Periodicity must be achieved on both the airfoil surface and the inflow/outflow boundaries. (2) Once periodicity is achieved, compute the pressure frequency spectra on the reference airfoil on both the upper and lower surfaces at x=(-0.25c,0.00, +0.25c), on the inflow boundary at (x,y)={1.5c,-0.3c), (-1.5c,0.0),(-1.5c,0.3c)} and on the outflow boundary at (x,y)= {(1.5c,-0.3c),(1.5c,0.0), (1.5c,0.3c)}. Express the spectral results in dB using the standard definition 20 log(P(sub(r.m.s)/P(sub ref), where p(sub ref) == 20 microPa. (3) Extract the harmonic pressure distributions on the inflow and outflow boundaries (i.e., on x= -/+ 1.5c lines) at the fundamental frequency omega and apply a Fourier transform in y direction to identify the spatial (i.e., mode order) structure of the pressure perturbations. Express the result in dB for each mode order. Repeat the process for the frequencies 2omega and 3omega.

Envia, Edmane↗
NASA NTRS2004

Category 3: Sound Generation by Interacting with a Gust

The cascade-gust interaction problem is solved employing a time-domain approach. The purpose of this problem is to test the ability of a CFD/CAA code to accurately predict the unsteady aerodynamic and aeroacoustic response of a single airfoil to a two-dimensional, periodic vortical gust.Nonlinear time dependent Euler equations are solved using higher order spatial differencing and time marching techniques. The solutions indicate the generation and propagation of expected mode orders for the given configuration and flow conditions. The blade passing frequency (BPF) is cut off for this cascade while higher harmonic, 2BPF and 3BPF, modes are cut on.

Scott, James R.↗
NASA NTRS2004

Category 5: Sound Generation in Viscous Problems

Two problems are considered. Problem 1: Aeolian tones, sound generation by flow over cylinders, are relevant to airframe and power plant noise (heat exchanger, power transmission lines and chimneys). The purpose of this problem is to test the ability of a CFD/CAA code to accurately predict sound generation by viscous flows and sound propagation through interactions between acoustic wave & solid wall and between acoustic waves & shear layers. Problem 2: Sound generation by flow over a cavity.Air flows over the cavity shown below with a mean approach flow velocity of 50 m/s. The boundary layer that develops over the flat plate is turbulent with a thickness of 14 mm at the entrance to the cavity. Calculate the power spectra at the center of each cavit wall and the center of the cavity floor. Experimental data will be available for comparison.

Lee, Soogab↗
NASA NTRS2004

Test-Analysis Correlation of a Crash Simulation of a Vertical Drop Test of a Commuter-Category Aircraft

A finite element model of an ATR42-300 commuter-class aircraft was developed and a crash simulation was executed. Analytical predictions were correlated with data obtained from a 30-feet per second (9.14-meters per second) vertical drop test of the aircraft. The purpose of the test was to evaluate the structural response of the aircraft when subjected to a severe, but survivable, impact. The aircraft was configured with seats, dummies, luggage, and other ballast. The wings were filled with 8,700 lb. (3,946 kilograms) of water to represent the fuel. The finite element model, which consisted of 57,643 nodes and 62,979 elements, was developed from direct measurements of the airframe geometry. The seats, dummies, luggage, simulated engines and fuel, and other ballast were represented using concentrated masses. The model was executed in LS-DYNA, a commercial finite element code for performing explicit transient dynamic simulations. Analytical predictions of structural deformation and selected time-history responses were correlated with experimental data from the drop test to validate the simulation.

Jackson, Karen E.↗
NASA NTRS2006

The Mars Microbeam Raman Spectrometer (MMRS): From Concept to Category-1 Proposal

Laser Raman Spectroscopy is flexible and can be deployed in many ways. The Mars Microbeam Raman Spectrometer (MMRS) is tailored for rover-based mobility platform and for Mars fundamental science objectives. The MMRS was initiated by science requirements to determine mineralogy, mineral chemistry, and molecular phase identification, including organics. MMRS is ready for any near term mission to Mars and the Moon. Science is the driving force for development.

mobility↗
NASA NTRS2015

Variability in the Propagation Phase of CFD-Based Noise Prediction: Summary of Results From Category 8 of the BANC-III Workshop

The usage of Computational Fluid Dynamics (CFD) in noise prediction typically has been a two part process: accurately predicting the flow conditions in the near-field and then propagating the noise from the near-field to the observer. Due to the increase in computing power and the cost benefit when weighed against wind tunnel testing, the usage of CFD to estimate the local flow field of complex geometrical structures has become more routine. Recently, the Benchmark problems in Airframe Noise Computation (BANC) workshops have provided a community focus on accurately simulating the local flow field near the body with various CFD approaches. However, to date, little effort has been given into assessing the impact of the propagation phase of noise prediction. This paper includes results from the BANC-III workshop which explores variability in the propagation phase of CFD-based noise prediction. This includes two test cases: an analytical solution of a quadrupole source near a sphere and a computational solution around a nose landing gear. Agreement between three codes was very good for the analytic test case, but CFD-based noise predictions indicate that the propagation phase can introduce 3dB or more of variability in noise predictions.

Lopes, Leonard↗
NASA NTRS2019

Pilot Evaluation of Proposed Go-Around Criteria for Transport Category Aircraft

The primary objective of this study was to capture pilot feedback and decision-making with regard to proposed, hypothetical, go-around criteria that were developed based on previous research. A secondary objective of the study was to assess crew members' awareness of the aircraft state on approach. An experiment was conducted using Boeing 737-800 and Airbus A330-200 level D full-flight simulators, in which pilots flew multiple approaches which were on the borderline of the proposed go-around criteria at 300 ft. Pilots were instructed that they could either execute a go-around or land the airplane on each run, forcing a decision for the borderline cases at 300 ft. Pilots were instructed to go around if the aircraft was outside of the go-around criteria at 300 ft or if either pilot was uncomfortable with the approach. The results revealed that: 1) the most important factors which drove go-around decision-making during the experiment were airspeed and localizer deviation, 2) the objective data suggested that the 300-ft gate is viable, although many pilots were still uncomfortable with that gate height; perhaps more emphasis on checking stability at 1,000 ft and 500 ft would make more pilots comfortable with the 300-ft go-around gate, 3) allowing for momentary deviations should be considered, and 4) the acceptability of the criteria is highly dependent on given pilot's risk tolerance. Overall, the proposed criteria performed well, and most pilots would find the criteria acceptable with some minor adjustments.

go-arounds↗
NASA NTRS2019

Best Practices for Evaluating Flight Deck Interfaces for Transport Category Aircraft with Particular Relevance to Issues of Attention, Awareness, and Understanding CAST SE-210 Output 2 Report 6 of 6

Attention, awareness, and understanding of the flight crew are a critical contributor to safety and the flight deck plays a critical role in supporting these cognitive functions. Changes to the flight deck need to be evaluated for whether the changed device provides adequate support for these functions. This report describes a set of diverse evaluation methods. The report recommends designing the interface-evaluation to span the phases of the device development, from early to late, and it provides methods appropriate at each phase. It describes the various ways in which an interface or interface component can fail to support awareness as potential issues to be assessed in evaluation. It summarizes appropriate methods to evaluate different issues concerning inadequate support for these functions, throughout the phases of development.

Billman, Dorrit O.↗
NASA NTRS2021

Go-Around Criteria Refinement for Transport Category Aircraft

Presently, airline pilots are trained to go around if, when lower than 500 ft above the ground, they are outside of a handful of parameters such as airspeed, position, and rate of descent. At times, pilots do not comply with these criteria, perhaps owing to their conservative nature or complexity. This paper examines potential refinements to the continue-to-land decision from the combined results of three flight simulator experiments. Potential refinements include simplifying the number of parameters and lowering the altitude at which pilots make the decision. First, refinements were developed by evaluating pilots’ touchdown performance and qualitative data in a variety of starting and environmental conditions. Second, 30 of those pilots evaluated the refinements under several induced instabilities during the approach. The results showed little difference in touchdown performance when lowering the decision altitude from 500 to 300 ft; however, significant differences arose when the decision altitude was lowered further to 100 ft. The proposed new criteria include assessments of deviations in airspeed and position, no rate-of-descent audio warning, and having an appropriate engine setting at 1000, 500, and 300 ft height above threshold. Additionally, a recommendation is made that if the proposed criteria are not met at the 1000 or 500 ft height above threshold the pilots may make corrections and continue the approach; however, if the criteria are not met at 300 ft, then a go-around should be performed.

stabilized approach criteria↗