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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Effects of velocity profile and inclination on dual-jet-induced pressures on a flat plate in a crosswind

An experimental study was conducted to determine surface pressure distributions on a flat plate with dual subsonic, circular jets exhausting from the surface into a crossflow. The jets were arranged in both side-by-side and tandem configurations and were injected at 90 deg and 60 deg angles to the plate, with jet-to-crossflow velocity ratio of 2.2 and 4. The major objective of the study was to determine the effect of a nonuniform (vs uniform) jet velocity profile, simulating the exhaust of a turbo-fan engine. Nonuniform jets with a high-velocity outer annulus and a low-velocity core induced stronger negative pressure fields than uniform jets with the same mass flow rate. However, nondimensional lift losses (lift loss/jet thrust lift) due to such nonuniform jets were lower than lift losses due to uniform jets. Changing the injection angle from 90 deg to 60 deg resulted in moderate (for tandem jets) to significant (for side-by-side jets) increases in the induced negative pressures, even though the surface area influenced by the jets tended to reduce as the angle decreased. Jets arranged in the side-by-side configuration led to significant jet-induced lift losses exceeding, in some cases, lift losses reported for single jets.

Jakubowski, A. L.↗
NASA NTRS2019

Assessment of Mixer-Ejector Nozzle with Thermal Acoustic Shield for Jet Noise Reduction

A tendency for excessive exhaust jet mixing noise from low bypass ratio turbofan engines is recognized as a key challenge in the design of commercial supersonic aircraft. In this work we investigate a unique combination of two noise mitigation methods as a novel strategy to reduce jet mixing noise. First, a thermal acoustic shield (TAS) is used to reflect high frequency acoustic waves at small angles to the jet axis; second, a mixer-ejector (ME) nozzle is used to mechanically shield noise propagating at large angles to the axis. The ME shroud also provides a convenient location for a TAS nozzle and improves TAS effectiveness by limiting the downstream extent of high frequency noise generation. In an additional benefit for a velocity-matched TAS stream, the ME allows a reduction in strength of the TAS outer shear layer which could serve as a secondary noise source. The present work provides a quantitative assessment of the ME-TAS concept, using a combination of RANS CFD simulations, acoustic analogy calculations for the farfield Green's function, and surrogate-based modeling and parameter space exploration. We first evaluate a subscale configuration, then use scaling arguments to apply subscale results to the systems-level analysis of a flight configuration; the latter configuration includes a generic low bypass ratio turbofan engine with an engine-driven electric generator for supplementary heating of the TAS stream. Additional RANS CFD calculations are performed for a notional ME-TAS geometry based on the full scale configuration, and various modeling assumptions and operational characteristics are evaluated. The ME-TAS concept is shown to provide effective shielding for high frequency jet noise, and should enable comparable noise suppression to a stand-alone ME of considerably greater length, weight and drag. In addition to investigating the integrated ME-TAS system, the present work differs from previous research into TAS and related fluidic shield concepts through the inclusion of modern numerical analysis tools and the systematic numerical examination of various design parameters.

thermal acoustic shield↗
NASA NTRS1964

Comments on exhaust flow field and surface impingement

In recent months there has been interest in the problem of the impingement of a jet exhaust on simulated lunar surfaces. The problem has been described both experimentally and theoretically. In the June issue of the AIAA Journal there appeared two Technical Notes that seemed to complicate unnecessarily the analysis of the free-jet expansion and the surface pressure distribution. The purpose of the present comment is to recall briefly the simple results of the theory and to make a more complete comparison with the experiniental data of Ref. 1

LUNAR SURFACE↗
NASA NTRS1973

Low-frequency rear quadrant noise of a turbojet engine with exhaust duct muffling

A J-65 engine was run with a tuned sound-absorbing exhaust duct to study the internal and jet components of rear quadrant noise. Full muffler, hard wall duct, and regular production engine configurations were tested. The jet exhaust velocities were subsonic. The use of the exhaust muffler extended the relation between the jet noise and the eighth power of the jet velocity to lower velocities than for the hard wall duct.

Woodward, R. P.↗
NASA NTRS1985

Effects of non-uniform velocity profiles on dual jets in a crossflow

The interaction between engine exhaust jets and the freestream affects the aerodynamic and stability characteristics of VTOL aircraft during the transition from hover to forward flight. This interaction is often modeled as a simple uniform jet issuing from a flat plate into a subsonic crossflow. The distribution of pressures induced by the jet on the surface of the plate can be used to predict the lift loss and pitching moment for a full-scale aircraft. The uniform jet model has limitations because an actual turbofan engine generates a rather nonuniform exit velocity profile. The purpose of this work is to study the effect of a nonuniform velocity profile on the surface pressure distribution. The mutual interaction of dual jets also is investigated in side-by-side and tandem configurations. Detailed pressure distributions are presented for two jet-to-freestream velocity ratios of 2.2 and 4.0. One important finding is that a nonuniform jet with a high velocity periphery and a low velocity core has a higher effective velocity ratio than a uniform jet with the same mass flow.

Moore, C. L.↗
NASA NTRS1975

Influence of multitube mixer nozzle geometry on CTOL-OTW jet noise shielding

Acoustic shielding benefits for CTOL over-the-wing (OTW) applications were obtained experimentally with various multitube nozzles using a simple board to represent a wing. Eight nozzles consisting of three to thirteen 2.36-cm diameter tubes were tested. The nozzles included single and double rings of tubes. Shielding surface lengths of 15.0 to 54.4 cm were used with each nozzle. Far-field noise data were obtained at 90 deg from the jet axis and with a nominal jet exhaust velocity of 200 m/sec. The jet noise shielding benefits for the nozzles with double rows of tubes, in terms of sound pressure level spectra, are correlated successfully as a function of an earlier developed parameter for nozzles with a single ring of tubes that includes consideration of the number of tubes and the local peak velocity in the flow field at the trailing edge of the shielding surface.

Vonglahn, U.↗
NASA NTRS1975

Influence of multitube mixer nozzle geometry on CTOL-OTW jet noise shielding

Acoustic shielding benefits for CTOL over-the-wing (OTW) applications were obtained experimentally with various multitube nozzles using a simple board to represent a wing. Eight nozzles consisting of three to thirteen 2.36-cm diameter tubes were tested. The nozzles included single and double rings of tubes. Shielding surface lengths of 15.0 to 54.4 cm were used with each nozzle. Far-field noise data were obtained at 90 deg from the jet axis and with a nominal jet exhaust velocity of 200 m/sec. The jet noise shielding benefits for the nozzles with double rows of tubes, in terms of sound pressure level spectra, are correlated successfully as a function of an earlier developed parameter for nozzles with a single ring of tubes that includes consideration of the number of tubes and the local peak velocity in the flow field at the trailing edge of the shielding surface.

Von Glahn, U.↗
NASA NTRS2010

Fifty Years of Fluidic Injection for Jet Noise Reduction

The paper reviews 50 years of research investigating jet noise reduction through fluidic injection. Both aqueous and gaseous injection concepts for supersonic and subsonic jet exhausts are discussed. Aqueous injection reduces jet noise by reducing main jet temperature through evaporation and main jet velocity through momentum transfer between water droplets and the main jet. In the launch vehicle environment where large quantities of fluid do not have to be carried with the vehicle, water injection is very effective at reducing excess overpressures. For in-flight use, aqueous injection is problematic as most studies show that either large quantities of water or high injection pressures are required to achieve noise reduction. The most effective noise reduction injection systems require water pressures above 2000 kPa (290 psi) and water-to-mainjet mass flow rates above 10% to achieve overall sound pressure level reductions of roughly 6 dB in the peak jet noise direction. Injection at lower pressure (roughly 1034 kPa or 150 psi) has resulted in a 1.6 EPNdb reduction in effective perceived noise level. Gaseous injection reduces noise through jet plume modifications resulting from the introduction of streamwise vorticity in the main jet. In subsonic single-stream jets, air injection usually produces the largest overall sound pressure level reductions (roughly 2 dB) in the peak jet noise direction. In dual-stream jets, properly designed injection systems can reduce overall sound pressure levels and effective perceived noise levels but care must be taken to choose injector designs that limit sound pressure level increases at high frequencies. A reduction of 1.0 EPNdB has been achieved with injection into the fan and core streams. However, air injection into dual-stream subsonic jets has received little attention and the potential for noise reduction is uncertain at this time. For dual-stream supersonic jets, additional research needs to be conducted to determine if reductions can be achieved with injection pressures available from current aircraft engines. 1.

Henderson, Brenda↗
NASA NTRS2013

The Effects of Surfaces on the Aerodynamics and Acoustics of Jet Flows

Aircraft noise mitigation is an ongoing challenge for the aeronautics research community. In response to this challenge, low-noise aircraft concepts have been developed that exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces manifest a complex behavior in which acoustic and aerodynamic characteristics are altered. In this paper, the variation of the aerodynamics, acoustic source, and far-field acoustic intensity are examined as a large at plate is positioned relative to the nozzle exit. Steady Reynolds-Averaged Navier-Stokes solutions are examined to study the aerodynamic changes in the field-variables and turbulence statistics. The mixing noise model of Tam and Auriault is used to predict the noise produced by the jet. To validate both the aerodynamic and the noise prediction models, results are compared with Particle Image Velocimetry (PIV) and free-field acoustic data respectively. The variation of the aerodynamic quantities and noise source are examined by comparing predictions from various jet and at plate configurations with an isolated jet. To quantify the propulsion airframe aeroacoustic installation effects on the aerodynamic noise source, a non-dimensional number is formed that contains the flow-conditions and airframe installation parameters.

Smith, Matthew J.↗
NASA NTRS1999

Aeroperformance and Acoustics of the Nozzle with Permeable Shell

Several simple experimental acoustic tests of a spraying system were conducted at the NASA Langley Research Center. These tests have shown appreciable jet noise reduction when an additional cylindrical permeable shell was employed at the nozzle exit. Based on these results, additional acoustic tests were conducted in the anechoic chamber AK-2 at the Central Aerohydrodynamics Institute (TsAGI, Moscow) in Russia. These tests examined the influence of permeable shells on the noise from a supersonic jet exhausting from a round nozzle designed for exit Mach number, M (sub e)=2.0, with conical and Screwdriver-shaped centerbodies. The results show significant acoustic benefits of permeable shell application especially for overexpanded jets by comparison with impermeable shell application. The noise reduction in the overall pressure level was obtained up to approximately 5-8%. Numerical simulations of a jet flow exhausting from a convergent-divergent nozzle designed for exit Mach number, M (sub e)=2.0, with permeable and impermeable shells were conducted at the NASA LaRC and Hampton University. Two numerical codes were used. The first is the NASA LaRC CFL3D code for accurate calculation of jet mean flow parameters on the basis of a full Navier-Stokes solver (NSE). The second is the numerical code based on Tam's method for turbulent mixing noise (TMN) calculation. Numerical and experimental results are in good qualitative agreement.

Gilinsky, M.↗
NASA NTRS2004

Jet Engine Noise Generation, Prediction and Control

Aircraft noise has been a problem near airports for many years. It is a quality of life issue that impacts millions of people around the world. Solving this problem has been the principal goal of noise reduction research that began when commercial jet travel became a reality. While progress has been made in reducing both airframe and engine noise, historically, most of the aircraft noise reduction efforts have concentrated on the engines. This was most evident during the 1950 s and 1960 s when turbojet engines were in wide use. This type of engine produces high velocity hot exhaust jets during takeoff generating a great deal of noise. While there are fewer commercial aircraft flying today with turbojet engines, supersonic aircraft including high performance military aircraft use engines with similar exhaust flow characteristics. The Pratt & Whitney F100-PW-229, pictured in Figure la, is an example of an engine that powers the F-15 and F-16 fighter jets. The turbofan engine was developed for subsonic transports, which in addition to better fuel efficiency also helped mitigate engine noise by reducing the jet exhaust velocity. These engines were introduced in the late 1960 s and power most of the commercial fleet today. Over the years, the bypass ratio (that is the ratio of the mass flow through the fan bypass duct to the mass flow through the engine core) has increased to values approaching 9 for modern turbofans such as the General Electric s GE-90 engine (Figure lb). The benefits to noise reduction for high bypass ratio (HPBR) engines are derived from lowering the core jet velocity and temperature, and lowering the tip speed and pressure ratio of the fan, both of which are the consequences of the increase in bypass ratio. The HBPR engines are typically very large in diameter and can produce over 100,000 pounds of thrust for the largest engines. A third type of engine flying today is the turbo-shaft which is mainly used to power turboprop aircraft and helicopters. An example of this type of engine is shown in Figure IC, which is a schematic of the Honeywell T55 engine that powers the CH-47 Chinook helicopter. Since the noise from the propellers or helicopter rotors is usually dominant for turbo-shaft engines, less attention has been paid to these engines in so far as community noise considerations are concerned. This chapter will concentrate mostly on turbofan engine noise and will highlight common methods for their noise prediction and reduction.

Huff, Dennis L.↗
NASA NTRS1984

An empirical method for predicting the mixing noise levels of subsonic circular and coaxial jets

An empirical method for predicting the static free field source noise levels of subsonic circular and coaxial jet flow streams is presented. The method was developed from an extensive data base of 817 jet tests obtained from five different government and industry sources in three nations. The prediction method defines the jet noise in terms of four components which are overall power level, power spectrum level, directivity index, and relative spectrum level. The values of these noise level components are defined on a grid consisting of seven frequency parameter values (Strouhal numbers) and seven directivity angles. The value of the noise level at each of these grid points is called a noise level coordinate and was defined as a function of five jet exhaust flow state parameters which are equivalent jet velocity, equivalent jet total temperature, the velocity ratio (outer stream to inner stream), temperature ratio, and area ratio. The functions were obtained by curve fitting in a least squares sense the noise level coordinates from the data base in a five dimensional flow state space using a third order Taylor series. The noise level coordinates define the component noise levels for all frequencies and directivities through a bicubic spline function.

Russell, J. W.↗
NASA NTRS1987

A multiple-time-scale turbulence model based on variable partitioning of turbulent kinetic energy spectrum

A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model.

Kim, S.-W.↗
NASA NTRS1989

A multiple-time-scale turbulence model based on variable partitioning of the turbulent kinetic energy spectrum

A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model.

Kim, S.-W.↗