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At least 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Experimental investigation of the performance of vortex generators mounted in the supersonic portion of a mixed-compression inlet

Vortex generators were investigated as a means of controlling the throat boundary layer in a Mach 2.5 mixed-compression inlet. With or without throat bleed, the generators were unable to produce the inlet peak recoveries available with good performance bleed. Generators placed on the unbled inlet centerbody ahead of the cowl shock impingement point degraded inlet performance. Generators placed further aft on the unbled centerbody, but ahead of the throat, improved inlet performance at conditions where the terminal shock could cause boundary layer separation. Adding generators to the inlet with throat bleed reduced performance. Bleed aft of the generators degraded the vortex flow field.

Michell, G. A.↗
NASA NTRS1971

Buckling analysis for axially compressed flat plates, structural sections, and stiffened plates reinforced with laminated composites

A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked plate and beam elements. Plates are idealized as multilayered orthotropic elements. Structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply-supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections, and stiffened plates is investigated. Buckling loads are the lowest of all possible general and local failure modes, and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections, and stiffened plates including boron-reinforced structures are discussed. In general correlations are reasonably good.

Viswanathan, A. V.↗
NASA NTRS1971

Compressive behavior of titanium alloy skin-stiffener specimens selectively reinforced with boron-aluminum composite

A method of selectively reinforcing a conventional titanium airframe structure with unidirectional boron-aluminum composite attached by brazing was successfully demonstrated in compression tests of short skin-stiffener specimens. In a comparison with all-titanium specimens, improvements in structural performance recorded for the composite-reinforced specimens exceeded 25 percent on an equivalent-weight basis over the range from room temperature to 700 K (800 F) in terms of both initial buckling and maximum strengths. Performance at room temperature was not affected by prior exposure at 588 K (600 F) for 1000 hours in air or by 400 thermal cycles between 219 K and 588 K (-65 F and 600 F). The experimental results were generally predictable from existing analytical procedures. No evidence of failure was observed in the braze between the boron-aluminum composite and the titanium alloy.

Herring, H. W.↗
NASA NTRS1971

An exact closed form solution for constant area compressible flow with friction and heat transfer

The well-known differential equation for the one-dimensional flow of a compressible fluid with heat transfer and wall friction has no known solution in closed form for the general case. This report presents a closed form solution for the special case of constant heat flux per unit length and constant specific heat. The solution was obtained by choosing the square of a dimensionless flow parameter as one of the independent variables to describe the flow. From this exact solution, an approximate simplified form is derived that is applicable for predicting subsonic flow performance characteristics for many types of constant area passages in internal flow. The data included in this report are considered sufficiently accurate for use as a guide in analyzing and designing internal gas flow systems.

Sturas, J. I.↗
NASA NTRS1971

Calculation of turbulent boundary layers with heat transfer and pressure gradient utilizing a compressibility transformation. Part 1: Summary report

The analysis uses a compressibility transformation and utilizes higher order closure rules to complete the transformation. By requiring that the momentum equations in differential form be satisfied at the wall and at the sublayer edge, correspondence rules are obtained which relate the variable property (VP) flow to a constant property (CP) flow in which mass transfer and pressure gradient occur simultaneously. A new CP formulation is developed and numerical results for a variety of cases are presented. Comparisons with earlier forms of the transformation and with experiment are included. For the zero pressure gradient case some differences between the various predictions are observed. For the several pressure gradient cases examined, the results are found to be essentially identical to those given by first order closure rules; i.e., by a form of transformation which relates the VP flow to a CP flow with pressure gradient but zero mass transfer.

Economos, C.↗
NASA NTRS1971

Operational procedure for computer program for design point characteristics of a compressed-air generator with through-flow combustor for V/STOL applications

The computer program described in this report calculates the design-point characteristics of a compressed-air generator for use in V/STOL applications such as systems with a tip-turbine-driven lift fan. The program computes the dimensions and mass, as well as the thermodynamic performance of a model air generator configuration which involves a straight through-flow combustor. Physical and thermodynamic characteristics of the air generator components are also given. The program was written in FORTRAN IV language. Provision has been made so that the program will accept input values in either SI units or U.S. customary units. Each air generator design-point calculation requires about 1.5 seconds of 7094 computer time for execution.

Krebs, R. P.↗
NASA NTRS1971

Structural efficiencies of five compression panels with curved elements

Structural-efficiency analyses are used to determine the minimum-mass proportions of some panel configurations loaded in uniaxial compression. Five panel constructions, four of which incorporate circular-arc elements and the other a beaded-web corrugation, are shown to have improved structural efficiencies over conventional configurations. In addition to the structural-efficiency equations, which give the mass equivalent flat-plate thickness of the panel necessary to carry a given load, related design equations for calculating the cross-sectional dimensions of these minimum-mass panels are presented. The upper and lower limits of loading, where the design constraints of minimum gage or material yield strength become the dominant design conditions, are established and the corresponding design equations which are applicable outside these limits are also presented.

Giles, G. L.↗
NASA NTRS1972

Tolerance of Mach 2.50 axisymmetric mixed-compression inlets to upstream flow variations

An investigation of the tolerances of two Mach 2.50 axisymmetric mixed-compression inlets to upstream flow variations was conducted. Tolerances of each inlet to angle of attack as a function of decreasing free-stream Mach number were obtained. A local region of overcompression was formed on the leeward side of the inlet at maximum angle of attack before unstart. This region of overcompression corresponded to local subsonic flow conditions ahead of the geometric throat. A uniform Mach number gradient of 0.10 at the cowl lip plane did not affect the inlet's pressure recovery, mass flow ratio, or diffuser exit total-pressure distortion.

Choby, D. A.↗
NASA NTRS1972

Investigation of a mixed compression axisymmetric inlet at Mach number 5.3

The hypersonic diffuser portion of an uncooled high performance mixed compression, axisymmetric inlet suitable for subsonic burning engines was designed and tested. Performance of a model with a 25.4-cm capture diameter was measured in a wind tunnel and the results were compared with theoretical predictions calculated by a comprehensive computer program. All tests were conducted at a Mach number of 5.3 at a total temperature of 667 K and a total pressure of 11.57 atm. The angle of attack ranged from 0 to + or - 3 deg. Performance at angle of attack remained high. Reasonably high performance in the throat (maximum throat pitot-pressure recovery of 77 percent and an average value of 58 percent) was obtained at 0 deg angle of attack with relatively large amounts of boundary-layer bleed (11 to 22 percent of the capture mass flow). The computer program used in the design of this inlet is considered marginally adequate for predicting hypersonic inlet flow fields. Although the program as it now exists is very useful, an improved computer program that more accurately predicts the boundary layer and the shock-wave-boundary-layer interaction and accounts for boundary-layer bleed should be developed for reliability predicting hypersonic inlet flow fields.

Latham, E. A.↗
NASA NTRS1971

A Numerical Study of Displacement Body and Curvature Effects on Incompressible and Compressible Laminar Boundary Layers

This technique has been applied to study such effects on incompressible flow around cylinders at moderate to low Reynolds numbers and for compression ramps at hypersonic Mach numbers by employing a finite difference method to obtain numerical solutions. The results indicate that the technique can be applied successfully in both regimes and does predict the correct trend in regions of large curvature and displacement body effects. It was concluded that curvature corrections should only be attempted in cases where all displacement effects can be fully accounted for.

Wornom, S. F.↗
NASA NTRS1969

Evaluation, construction and endurance testing of compression sealed pyrolytic boron nitride slot insulation

A high-temperature statorette, consisting of an iron-27 percent cobalt magnetic lamination stack and nickel-clad silver conductors, was tested with pyrolytic boron nitride slot insulation. Temperatures were measured in each test to determine characteristics of slot linear heat conductance from statorette conductors. Testing was carried out to temperatures of approximately 1500 F in a vacuum environment of 10-8 torr. Three assemblies were built and tested, each having a different room temperature slot clearance. The final statorette assembly was subjected to a 100-hour vacuum aging test at 1400 F followed by 25 thermal cycles. Temperature data from the three assemblies showed that decreasing slot clearance and increasing compression loading did enhance heat transfer. The temperature difference between slot and lamination at 1400 F increased 4 F during the thermal aging and an additional 10 F during the 25 thermal cycles.

Grant, W. L.↗
NASA NTRS1972

Computer program for solving compressible nonsimilar-boundary-layer equations for laminar, transitional, or turbulent flows of a perfect gas

A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity.

Price, J. M.↗
NASA NTRS1972

Quasi-one-dimensional compressible flow across face seals and narrow slots. 1: Analysis

An analysis is presented for compressible fluid flow across shaft face seals and narrow slots. The analysis includes fluid inertia, viscous friction, and entrance losses. Subsonic and choked flow conditions can be predicted and analyzed. The model is valid for both laminar and turbulent flows. Results agree with experiment and with solutions which are more limited in applicability. Results show that a parallel film can have a positive film stiffness under choked flow conditions.

Zuk, J.↗
NASA NTRS1972

Effects of eccentricities and lateral pressure on the design of stiffened compression panels

An analysis for determining the effects of eccentricities and lateral pressure on the design of stiffened compression panels is presented. The four types of panel stiffeners considered are integral, zee, integral zee, and integral tee. Mass-strength curves, which give the mass of the panel necessary to carry a specified load, are given along with related design equations needed to calculate the cross-sectional dimensions of the minimum-mass-stiffened panel. The results of the study indicate that the proportions of the panels are geometrically similar to the proportions of panels designed for no eccentricity or lateral pressure, but no cross-sectional dimensions are greater, resulting in significantly increased mass. The analytical minimum-mass designs of zee-stiffened panels are compared with designs from experimentally derived charts. An assumed eccentricity of 0.001 times the length of the panel is used to correlate the analytical and experimental data. Good correlation between the experimentally derived and the analytical curves is obtained for the range of loading where materials yield governs the design. At lower loads the mass given by the analytical curve using this assumed eccentricity is greater than that given by the experimental results.

Giles, G. L.↗
NASA NTRS1972

Computer program for calculating laminar and turbulent boundary layer development in compressible flow

A computer program is described which performs a numerical integration of the equations of motion for a compressible two-dimensional boundary layer. Boundary layer calculations may be carried out for both laminar and turbulent flow for arbitrary Reynolds number and free stream Mach number distribution on planar or axisymmetric bodies with wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and a rough or a smooth wall. A variety of options are available as initial conditions. The program can generate laminar initial conditions such as Falkner-Skan similarity solutions (so that initial wedge flows can be simulated including Blasius or stagnation point flow) or approximate equilibrium turbulent profiles. Alternatively, initial profile input data can be utilized.

Herring, H. J.↗
NASA NTRS1972

Optimum mass-strength analysis for orthotropic ring-stiffened cylinders under axial compression

An analysis was developed to calculate the minimum mass-strength curve for an orthotropic cylinder subjected to axial compressive loading. The analysis, which includes the effects of ring and stringer eccentricities, is in a general form so that various cylinder wall and stiffener geometries can be considered. Several different ring-stiffened orthotropic configurations were studied. The minimum mass-strength curves and the dimensions associated with these curves are presented for (in order of decreasing efficiency) a tubular double bead, a nonsymmetric double bead, a Z-stiffened skin, and a trapezoidal corrugation. A comparison of efficiencies of the configurations shows a tubular element cylinder to be more efficient than a 3-percent core-density honeycomb-sandwich cylinder. It was found that for an optimized Z-stiffened skin, the location of the Z-stiffeners (internal or external) made a negligible difference in efficiency.

Shideler, J. L.↗
NASA NTRS1972

Digital-computer normal shock position and restart control of a Mach 2.5 axisymmetric mixed-compression inlet

Digital computer control of a mixed-compression inlet is discussed. The inlet was terminated with a choked orifice at the compressor face station to dynamically simulate a turbojet engine. Inlet diffuser exit airflow disturbances were used. A digital version of a previously tested analog control system was used for both normal shock and restart control. Digital computer algorithms were derived using z-transform and finite difference methods. Using a sample rate of 1000 samples per second, the digital normal shock and restart controls essentially duplicated the inlet analog computer control results. At a sample rate of 100 samples per second, the control system performed adequately but was less stable.

Neiner, G. H.↗
NASA NTRS1972

An invariant second-order closure model of the compressible turbulent boundary layer on a flat plate

The development of an invariant model designed expressly for the computation of shear flows is discussed. The model for incompressible layers seeks a second-order closure of the equations for the mean and fluctuating fields. The development of a method for computing the behavior of shear layers in compressible forces is described. The complexity of the analysis is restrained by limiting the consideration to a flat plate boundary layer where the mean pressure can be taken to be constant.

Donaldson, C. D.↗