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Results for “Drag coefficient”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Models of Lift and Drag Coefficients of Stalled and Unstalled Airfoils in Wind Turbines and Wind Tunnels

Equations are developed with which to calculate lift and drag coefficients along the spans of torsionally-stiff rotating airfoils of the type used in wind turbine rotors and wind tunnel fans, at angles of attack in both the unstalled and stalled aerodynamic regimes. Explicit adjustments are made for the effects of aspect ratio (length to chord width) and airfoil thickness ratio. Calculated lift and drag parameters are compared to measured parameters for 55 airfoil data sets including 585 test points. Mean deviation was found to be -0.4 percent and standard deviation was 4.8 percent. When the proposed equations were applied to the calculation of power from a stall-controlled wind turbine tested in a NASA wind tunnel, mean deviation from 54 data points was -1.3 percent and standard deviation was 4.0 percent. Pressure-rise calculations for a large wind tunnel fan deviated by 2.7 percent (mean) and 4.4 percent (standard). The assumption that a single set of lift and drag coefficient equations can represent the stalled aerodynamic behavior of a wide variety of airfoils was found to be satisfactory.

Spera, David A.↗
NASA NTRS1984

Method to estimate drag coefficient at the air/ice interface over drifting open pack ice from remotely sensed data

A knowledge in near real time, of the surface drag coefficient for drifting pack ice is vital for predicting its motions. And since this is not routinely available from measurements it must be replaced by estimates. Hence, a method for estimating this variable, as well as the drag coefficient at the water/ice interface and the ice thickness, for drifting open pack ice was developed. These estimates were derived from three-day sequences of LANDSAT-1 MSS images and surface weather charts and from the observed minima and maxima of these variables. The method was tested with four data sets in the southeastern Beaufort sea. Acceptable results were obtained for three data sets. Routine application of the method depends on the availability of data from an all-weather air or spaceborne remote sensing system, producing images with high geometric fidelity and high resolution.

Feldman, U.↗
NASA NTRS1988

Measurements of droplet drag coefficients in a polydispersed turbulent flow field

Measurements of drag coefficient versus Reynolds number were obtained in a polydispersed turbulent flow field for three turbulence velocities and for freestream turbulence intensities between 3 and 12 percent. Results are presented for a single nozzle with low number density and a twin nozzle with higher number density. The results for drops smaller than 30 microns showed strong differences from existing low turbulence results. The drag relation was found to be weakly affected by the freestream velocity and to be strongly affected by the velocity fluctuation levels of individual size classes. A drag effect with the drop-drop interaction may also be possible.

Rudoff, R. C.↗
DOE OSTI2023

Heavy-Duty Vehicle Air Drag Coefficient Estimation: From an Algebraic Perspective

When a heavy-duty vehicle (HDV) operates at the nominal highway speed, over two-thirds of its total resistive force comes from the air drag, contributing to more than half of its fuel consumption. One effective countermeasure to reduce the fuel consumption of HDVs is platooning, which employs connectivity and automated driving technologies to link two or more HDVs in convoy. Platooning allows HDVs to drive closer together and yields improved fuel economy and less CO2 emission thanks to the reduced air drag. Maximizing the energy benefits of an HDV platoon requires quantifying the drag interaction between vehicles. In practice, modeling the drag reduction in a platoon boils down to identifying the relationship between the air drag coefficient C d and the inter-vehicle distance d. Existing approaches to identify C d (d) include vehicle field tests, wind tunnel experiments, and computational fluid dynamics simulation, which can howbeit be time-consuming and cost prohibitive. In contrast, this paper proposes an algebraic approach, which relies on onboard-measurable variables, to estimate the air drag coefficient of an HDV in a platoon. Its algebraic nature avoids the classical persistence of excitation condition for parameter identification and can yield the identified parameter almost instantaneously. Simulation results demonstrate its effectiveness and the improved estimation speed over a recursive least squares identifier.

Wang, Zejiang↗
NASA NTRS1987

Evaluation of icing drag coefficient correlations applied to iced propeller performance prediction

Evaluation of three empirical icing drag coefficient correlations is accomplished through application to a set of propeller icing data. The various correlations represent the best means currently available for relating drag rise to various flight and atmospheric conditions for both fixed-wing and rotating airfoils, and the work presented here ilustrates and evaluates one such application of the latter case. The origins of each of the correlations are discussed, and their apparent capabilities and limitations are summarized. These correlations have been made to be an integral part of a computer code, ICEPERF, which has been designed to calculate iced propeller performance. Comparison with experimental propeller icing data shows generally good agreement, with the quality of the predicted results seen to be directly related to the radial icing extent of each case. The code's capability to properly predict thrust coefficient, power coefficient, and propeller efficiency is shown to be strongly dependent on the choice of correlation selected, as well as upon proper specificatioon of radial icing extent.

Miller, Thomas L.↗
NASA NTRS1972

A review of sphere drag coefficients applicable to atmospheric density sensing

A comprehensive search has been performed on the drag coefficient of spheres in the Reynolds number range from 50 to 50,000 and for Mach numbers up to 5. This Reynolds-Mach number range corresponds to the range of interest in the falling sphere technique of atmospheric sensing. In this technique, the knowledge of the sphere's trajectory and its aerodynamic characteristics are utilized to obtain the density of the atmosphere. Presently available data have been collected and analyzed as to their validity and applicability to atmospheric density measurements. A new drag table is recommended for use in these measurements.

Krumins, M. V.↗
NASA NTRS1975

Drag coefficient of 20-degree conical ribbon parachute

An empirical formula for the steady-state drag coefficient of a 20-degree conical ribbon parachute is developed. The derived expression takes into account the effect of suspension line length and geometric porosity within the limits of practical design. Also included are factors which provide drag reduction due to skirt reefing and the wake behind a primary body. The calculated values are in agreement with the available experimental results.

Utreja, L. R.↗
NASA NTRS1975

Prediction of the drag coefficient of a 20-degree conical ribbon parachute

An empirical formula for the steady state drag coefficient of a 20 degree conical ribbon parachute is developed. The derived expression takes into account the effect of suspension line length and geometric porosity within the limits of practical design. Also included are factors which provide drag reduction due to skirt reefing and the wake behind a primary body. The calculated values are in agreement with the available experimental results.

Utreja, L. R.↗