Results for “Internal and external flows” — Page 9

NASA NTRSDate not supplied

Linear Interaction Approximation for the Prediction of Noise Generated by Turbulence/Shock Interactions

In this paper we review the basic development of Linear Interaction Approximation (LIA), a linear inviscid approach to study the interaction of weak turbulence with flow discontinuities, and implement a formulation to calculate the acoustic field due to the incidence of vortical and entropic disturbances on a planar shock. The work is motivated by the observance in nozzles with internal mixers and external plugs of a shock formed by local flow accelerations, even at sub-critical pressure ratios. Exhaust systems with internally mixed/externally plugged nozzles are currently under consideration for use in commercial supersonic aircraft and it is important to have an assessment of the impact of this shock on the noise radiated by these nozzles. Numerical results are presented for the fluctuating pressure emitted by (separate) incident single-wave vorticity and entropy modes and for incident isotropic fields of turbulence and entropy. Further applications of the formulation to the flow fields in internally mixed/externally plugged nozzles, and to the modification of mixing noise sources and the scattering of internally generated noise by the shock, are discussed as future work.

Jet noise, shock waves, aircraft noise↗

NASA NTRSDate not supplied

Linear Interaction Approximation for the Prediction of Noise Generated by Turbulence/Shock Interaction

In this paper we review the basic development of Linear Interaction Approximation (LIA), a linear inviscid approach to study the interaction of weak turbulence with flow discontinuities, and implement a formulation to calculate the acoustic field due to the incidence of vortical and entropic disturbances on a planar shock. The work is motivated by the observance in nozzles with internal mixers and external plugs of a shock formed by local flow accelerations, even at sub-critical pressure ratios. Exhaust systems with internally mixed/externally plugged nozzles are currently under consideration for use in commercial supersonic aircraft and it is important to have an assessment of the impact of this shock on the noise radiated by these nozzles. Numerical results are presented for the fluctuating pressure emitted by (separate) incident single-wave vorticity and entropy modes and for incident isotropic fields of turbulence and entropy. Further applications of the formulation to the flow fields in internally mixed/externally plugged nozzles, and to the modification of mixing noise sources and the scattering of internally generated noise by the shock, are discussed as future work.

Jet noise↗

NASA NTRS1985

Performance Improvement for Nonaxisymmetric Nozzles

Internal flow separation eliminated during reverse thrust. Convergent and Divergent Nozzle Flaps rotate to form reverser blocker for reverse-thrust operation. During cruise operation, drums rotate in direction of external flow. During reverse-thrust operation, drums rotate in direction of internal flow. Rotating-drum thrust reverser and boundarylayer control device improves performance of nonaxisymmetric nozzles in three ways: (1) Controls thrust-reverser exhaust port area by elimination of internal flow separation in reverser exhaust port; (2) provides control of reverse-thrust flow direction (exhaust angle); and (3) eliminates external flow separation over nozzle boattail.

Berrier, B. L.↗

NASA NTRS1986

Pretest Report for the Full Span Propulsive Wing/Canard Model Test in the NASA Langley 4 x 7 Meter Low Speed Wind Tunnel Second Series Test

A full span propulsive wing/canard model is to be tested in the NASA Langley Research Center (LaRC) 4 x 7 meter low speed wind tunnel. These tests are a continuation of the tests conducted in Feb. 1984, NASA test No.290, and are being conducted under NASA Contract NAS1-17171. The purpose of these tests is to obtain extensive lateral-directional data with a revised fuselage concept. The wings, canards, and vertical tail of this second test series model are the same as tested in the previous test period. The fuselage and internal flow path have been modified to better reflect an external configuration suitable for a fighter airplane. Internal ducting and structure were changed as required to provide test efficiency and blowing control. The model fuselage tested during the 1984 tests was fabricated with flat sides to provide multiple wing and canard placement variations. The locations of the wing and canard are important variables in configuration development. With the establishment of the desired relative placement of the lifting surfaces, a typically shaped fuselage has been fabricated for these tests. This report provides the information necessary for the second series tests of the propulsive wing/canard model. The discussion in this report is limited to that affected by the model changes and to the second series test program. The pretest report information for test 290 which is valid for the second series test was published in Rockwell report NR 83H-79. This report is presented as Appendix 1 and the modified fuselage stress report is presented as Appendix 2 to this pretest report.

Stewart, V. R.↗

NASA NTRSDate not supplied

Diagnosing Noise Features Of Internally Mixed, External Plug Exhaust Systems

In internally mixed exhaust systems, a lobed or forced mixer is employed to mix the core and bypass streams before they exit the common nozzle. For moderate bypass-ratio engines this marginally improves thrust, and provides a significant acoustic benefit. Indeed, it has been thought that a fully mixed jet creates the lowest noise you can get from a two-stream engine. Typically, the forced mixer system produces a bit more noise than a fully mixed equivalent jet, noise that has been called “excess noise”. In recent testing, this excess noise seemed to be amplified when an external plug was employed in the exhaust system to reduce boattail drag. Identifying the mechanism of this excess noise and mitigating it is key to creating commercial supersonic vehicles that are acoustically acceptable around airports. This paper adds to that investigation, analyzing results from recent tests where far-field acoustic data were acquired on two sets of flows with matched fully mixed flow conditions. One set of flows had a heated core stream, making it a dual-stream jet. The other set had both streams heated to the same temperature, making a single-stream jet that matched the fully mixed temperature and velocity of the dual-stream jet. These flows were tested in two lobed-mixer exhaust systems with internal and external plugs. Analysis of flow and noise data from the nozzles with combinations of single- and dual-stream flows, and with and without flight streams, gives insight into how and why the noise of the dual-stream and single-stream jet differ. One additive source, present in nozzles both with and without external plugs, comes from inside the nozzle, likely the internal shear layer coming off the lobed mixer. This noise source is not impacted by a change in flight stream and has a distinctive spectral directivity that is amplified by the presence of the external plug. Finding the exact source mechanism of this new source will be key to making the internally mixed exhaust systems reach their lowest possible sound level.

Noise prediction, supersonic, jet noise↗

NASA NTRSDate not supplied

Diagnosing Noise Features Of Internally Mixed, External Plug Exhaust Systems

In internally mixed exhaust systems, a lobed or forced mixer is employed to mix the core and bypass streams before they exit the common nozzle. For moderate bypass-ratio engines this marginally improves thrust, and provides a significant acoustic benefit. Indeed, it has been thought that a fully mixed jet creates the lowest noise you can get from a two-stream engine. Typically, the forced mixer system produces a bit more noise than a fully mixed equivalent jet, noise that has been called “excess noise”. In recent testing, this excess noise seemed to be amplified when an external plug was employed in the exhaust system to reduce boattail drag. Identifying the mechanism of this excess noise and mitigating it is key to creating commercial supersonic vehicles that are acoustically acceptable around airports. This paper adds to that investigation, analyzing results from recent tests where far-field acoustic data were acquired on two sets of flows with matched fully mixed flow conditions. One set of flows had a heated core stream, making it a dual-stream jet. The other set had both streams heated to the same temperature, making a single-stream jet that matched the fully mixed temperature and velocity of the dual-stream jet. These flows were tested in two lobed-mixer exhaust systems with internal and external plugs. Analysis of flow and noise data from the nozzles with combinations of single- and dual-stream flows, and with and without flight streams, gives insight into how and why the noise of the dual-stream and single-stream jet differ. One additive source, present in nozzles both with and without external plugs, comes from inside the nozzle, likely the internal shear layer coming off the lobed mixer. This noise source is not impacted by a change in flight stream and has a distinctive spectral directivity that is amplified by the presence of the external plug. Finding the exact source mechanism of this new source will be key to making the internally mixed exhaust systems reach their lowest possible sound level.

Noise prediction↗

NASA NTRS1951

Low-Lift Drag and Duct Pressure Recovery of a 1/8.25-Scale Model of the Consolidated Vultee XF-92 Airplane at Mach Numbers from 0.7 to 1.4

A flight investigation has been made to determine the external drag and pressure recovery of a 1/8.25 - scale flight model of the Consolidated Vultee XF-92 from Mach numbers 0.7 to 1.4 and Reynolds numbers from 8.5 x 10(exp 6) to 19.2 x 10(exp 6) at or near zero lift. Relative mass flow, average pressure recovery, total drag, internal drag, and external drag are presented as functions of Mach number. Between Mach numbers of 0.90 and 0.975, the external drag of the configuration (including base drag of the inner body and additive drag) was about equal to that of a similar model with a faired nose and no mass flow; however, at supersonic speeds the drag coefficient for the faired-nose model remained relatively constant whereas the drag coefficient for the ducted model continued to increase sharply. The internal drag coefficient of the duct was roughly constant at 0.013 up to a Mach number of 1.20; after which it decreased to 0.0075 at a Mach number of 1.4. The over-all pressure recovery of the inlet and duct varied from 94 percent at a Mach number of 0.7 to about 91 percent at a Mach number of 1.4 at a relative-mass-flow ratio of about 0.30. The losses in pressure recovery were believed to be caused by the possible occurrence of separation of flow from the inner body and by an aerodynamically unclean internal configuration which did not duplicate the form proposed for the original XF-92 airplane.

Mitcham, Grady L.↗

NASA NTRS1988

Three-dimensional incompressible Navier-Stokes computations of internal flows

Several incompressible Navier-Stokes solution methods for obtaining steady and unsteady solutions are discussed. Special attention is given to internal flows which involve distinctly different features from external flows. The characterisitcs of the flow solvers employing the method of pseudocompressibility and a fractional step method are briefly described. This discussion is limited to a primitive variable formulation in generalized curvilinear coordinates. Computed results include simple test cases and internal flow in the Space Shuttle main engine hot-gas manifold.

Kwak, D.↗

NASA NTRS1975

Acoustic characteristics of a large scale wind-tunnel model of a jet flap aircraft

The expanding-duct jet flap (EJF) concept is studied to determine STOL performance in turbofan-powered aircraft. The EJF is used to solve the problem of ducting the required volume of air into the wing by providing an expanding cavity between the upper and lower surfaces of the flap. The results are presented of an investigation of the acoustic characteristics of the EJF concept on a large-scale aircraft model powered by JT15D engines. The noise of the EJF is generated by acoustic dipoles as shown by the sixth power dependence of the noise on jet velocity. These sources result from the interaction of the flow turbulence with flap of internal and external surfaces and the trailing edges. Increasing the trailing edge jet from 70 percent span to 100 percent span increased the noise 2 db for the equivalent nozzle area. Blowing at the knee of the flap rather than the trailing edge reduced the noise 5 to 10 db by displacing the jet from the trailing edge and providing shielding from high-frequency noise. Deflecting the flap and varying the angle of attack modified the directivity of the underwing noise but did not affect the peak noise. A forward speed of 33.5 m/sec (110 ft/sec) reduced the dipole noise less than 1 db.

Falarski, M. D.↗

NASA NTRS1977

Interactive calculation procedure for supersonic flows

An interactive procedure was developed for supersonic viscous flows that can be used for either two-dimensional or axisymmetric configurations. The procedure is directed to supersonic internal flows as well as those supersonic external flows that require consideration of mutual interaction between the outer flow and the boundary layer flow. The flow field is divided into two regions: an inner region which is highly viscous and mostly subsonic and an outer region where the flow is supersonic and in which viscous effects are small but not negligible. For the outer region a numerical solution is obtained by applying the method of characteristics to a system of equations which includes viscous and conduction transport terms only normal to the streamlines. The inner region is treated by a system of equations of the boundary layer type that includes higher order effects such as longitudinal and transverse curvature and normal pressure gradients. These equations are coupled and solved simultaneously in the physical coordinates by using an implicit finite difference scheme. This system can also be used to calculate laminar and turbulent boundary layers using a scalar eddy viscosity concept.

Tassa, Y.↗

NASA NTRS1988

MODIS Information, Data, and Control System (MIDACS) system specifications and conceptual design

The MODIS Information, Data, and Control System (MIDACS) Specifications and Conceptual Design Document discusses system level requirements, the overall operating environment in which requirements must be met, and a breakdown of MIDACS into component subsystems, which include the Instrument Support Terminal, the Instrument Control Center, the Team Member Computing Facility, the Central Data Handling Facility, and the Data Archive and Distribution System. The specifications include sizing estimates for the processing and storage capacities of each data system element, as well as traffic analyses of data flows between the elements internally, and also externally across the data system interfaces. The specifications for the data system, as well as for the individual planning and scheduling, control and monitoring, data acquisition and processing, calibration and validation, and data archive and distribution components, do not yet fully specify the data system in the complete manner needed to achieve the scientific objectives of the MODIS instruments and science teams. The teams have not yet been formed; however, it was possible to develop the specifications and conceptual design based on the present concept of EosDIS, the Level-1 and Level-2 Functional Requirements Documents, the Operations Concept, and through interviews and meetings with key members of the scientific community.

Han, D.↗

NASA NTRS1992

A nozzle internal performance prediction method

A prediction method was written and incorporated into a three-dimensional Navier-Stokes code (PAB3D) for the calculation of nozzle internal performance. The following quantities are calculated: (1) discharge coefficient; (2) normal, side, and axial thrust ratios; (3) rolling, pitching, and yawing moments; and (4) effective pitch and yaw vector angles. Four different case studies are presented to confirm the applicability of the methodology. Internal and, in most situations, external flow-field regions are required to be modeled. The computed nozzle discharge coefficient matches both the level and the trend of the experimental data within quoted experimental data accuracy (0.5 percent). Moment and force ratios are generally within 1 to 2 percent of the absolute level of experimental data, with the trends of data matched accurately.

Carlson, John R.↗

NASA NTRS1992

Analysis of a space emergency ammonia dump using the FLOW-NET two-phase flow program

Venting of cryogenic and non-cryogenic fluids to a vacuum or a very low pressure will take place in many space-based systems that are currently being designed. This may cause liquid freezing either internally within the flow circuit or on external spacecraft surfaces. Typical ammonia flow circuits were investigated to determine the effect of the geometric configuration and initial temperature, pressure, and void fraction on the freezing characteristics of the system. The analysis was conducted also to investigate the ranges of applicability of the FLOW-NET program. It was shown that a typical system can be vented to very low liquid fractions before freezing occurs. However, very small restrictions in the flow circuit can hasten the inception of freezing. The FLOW-NET program provided solutions over broad ranges of system conditions, such as venting of an ammonia tank, initially completely filled with liquid, through a series of contracting and expanding line cross sections to near-vacuum conditions.

Navickas, J.↗

NASA NTRS1993

Numerical simulation of non-Newtonian free shear flows

Free shear flows, like those of mixing layers, are encountered in aerodynamics, in the atmosphere, and in the ocean as well as in many industrial applications such as flow reactors or combustion chambers. It is, therefore, crucial to understand the mechanisms governing the process of transition to turbulence in order to predict and control the evolution of the flow. Delaying transition to turbulence as far downstream as possible allows a gain in energy expenditure while accelerating the transition can be of interest in processes where high mixing is desired. Various methods, including the use of polymer additives, can be effective in controlling fluid flows. The drag reduction obtained by the addition of small amounts of high polymers has been an active area of research for the last three decades. It is now widely believed that polymer additives can affect the stability of a large variety of flows and that dilute solutions of these polymers have been shown to produce drag reductions of over 80 percent in internal flows and over 60 percent in external flows under a wide range of conditions. The major thrust of this work is to study the effects of polymer additives on the stability of the incompressible mixing layer through large scale numerical simulations. In particular, we focus on the two dimensional flow and examine how the presence of viscoelasticity may affect the typical structures of the flow, namely roll-up and pairing of vortices.

Homsy, G. M.↗

NASA NTRS2009

Proceedings of Minnowbrook Workshops I to VI

This DVD collection includes the complete proceedings of Minnowbrook Workshops I through VI. Titles include Minnowbrook I - 1993 Workshop on End-Stage Boundary Layer Transition (NASA/CP-2007-214667, CASI ID 20070038942), Minnowbrook II - 1997 Workshop on Boundary Layer Transition in Turbomachines (NASA/CP-1998-206958, CASI ID 19980206205), Minnowbrook III - 2000 Workshop on Boundary Layer Transition and Unsteady Aspects of Turbomachinery Flow (NASA/CP-2001-210888, CASI ID 20020067662), Minnowbrook IV - 2003 Workshop on Transition and Unsteady Aspects of Turbomachinery Flows (NASA TM-2004-212913, CASI ID 20040121174), Minnowbrook V - 2006 Workshop on Unsteady Flows in Turbomachinery (NASA/CP-2006-214484, CASI ID 20070024781), and Minnowbrook VI - 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics (NASA/CP-2010-216112, CASI ID 20100018557).

John E. Lagraff↗

NASA NTRS1983

Interactive calculation procedures for mixed compression inlets

The proper design of engine nacelle installations for supersonic aircraft depends on a sophisticated understanding of the interactions between the boundary layers and the bounding external flows. The successful operation of mixed external-internal compression inlets depends significantly on the ability to closely control the operation of the internal compression portion of the inlet. This portion of the inlet is one where compression is achieved by multiple reflection of oblique shock waves and weak compression waves in a converging internal flow passage. However weak these shocks and waves may seem gas-dynamically, they are of sufficient strength to separate a laminar boundary layer and generally even strong enough for separation or incipient separation of the turbulent boundary layers. An understanding was developed of the viscous-inviscid interactions and of the shock wave boundary layer interactions and reflections.

Reshotko, Eli↗

NASA NTRS1993

Three-dimensional hypersonic rarefied flow calculations using direct simulation Monte Carlo method

A summary of three-dimensional simulations on the hypersonic rarefied flows in an effort to understand the highly nonequilibrium flows about space vehicles entering the Earth's atmosphere for a realistic estimation of the aerothermal loads is presented. Calculations are performed using the direct simulation Monte Carlo method with a five-species reacting gas model, which accounts for rotational and vibrational internal energies. Results are obtained for the external flows about various bodies in the transitional flow regime. For the cases considered, convective heating, flowfield structure and overall aerodynamic coefficients are presented and comparisons are made with the available experimental data. The agreement between the calculated and measured results are very good.

Celenligil, M. Cevdet↗

NASA NTRS1957

Interference Effects of Fuselage-Stored Missiles on Inlet Duct Model of an Interceptor-Type Aircraft at Mach Numbers 1.5 to 1.9

The effect of missile armament on the performance of an interceptor-type aircraft model has been determined at Mach numbers 1.5, 1.7, and 1.9 and at angles of attack to 19 deg. With this configuration missiles were carried in a bay located on the bottom of the aircraft fuselage and mounted to a rotatable missile door. Rotation of the door then brought the missiles into the external or firing position. The aircraft model was characterized by triangular-shaped normal-shock inlets located at the wing roots. Relatively short and curved subsonic diffusers fed simulated twin side-by-side turbojet engines. Inasmuch as the missile bay extended considerably ahead of the inlet station, rotation of the missile door created considerable disturbance of the flow entering the inlets. In comparison with the internal missile arrangement, the external missile configurations increased the model lift, drag, and pitching moment. While the diffuser-exit flow distortion and static-pressure fluctuations were not greatly affected, diffuser total-pressure recovery was reduced as much as 0.058 at Mach number 1.9 for one missile configuration. The most detrimental effect of missile-door rotation occurred at the transient door positions, or with the door halfwzy between the missiles-in and -out conditions. At this door position the flow into the inlets was highly asymmetrical. Although the performance of both left and right ducts was generally reduced, the inlet duct on the cavity side of the missile door was most severely penalized, becoming unstable recovery losses and increases in flow distortion. The installation of fuselage fences along the missile bay was only partially effective in reducing these losses.

Piercy, T. G.↗