Core Stream Research Articles

Some Aspects of Modeling Compressor Behavior in Gas Turbine Performance Calculations

Performance calculation procedures for gas turbine engines are usually based on the performance characteristics of the engine components, and especially the turbo components are of major interest. In this paper methods of modelling compressors in gas turbine performance calculations are discussed. The basic methodologies based on Mach number similarity are summarized briefly including some second order effects. Under extreme engine partload conditions, as for example subidle or windmilling, the operating points in the compressor map are located in a region which is usually not covered by rig tests. In addition the parameters usually used in compressor maps are no longer appropriate. For these operating conditions a method is presented to extrapolate compressor maps towards very low spool speed down to the locked rotor. Instead of the efficiency more appropriate parameters as for example specific work or specific torque are suggested. A compressor map prepared with the proposed methods is presented and discussed. As another relevant topic the performance modelling of fans for low bypass ratio turbofans is covered. Due to the flow splitter downstream of such a fan the core and bypass stream may be throttled independently during engine operation and bypass ratio becomes a third independent parameter in the map. Because testing a fan on the rig for various bypass ratios is a very costly task, a simplified method has been developed which accounts for the effects of bypass ratio.

A Review of the ‘Value’ Literature and Implications for Relationship Marketing

The creation and delivery of value to customers is of increasing interest to researchers and practitioners. This paper identifies and reviews nine core streams of literature that have been influential on current research in the field of customer value. It argues that while much of the literature has focused on value creation for the customer, the relationship-marketing paradigm demands a broader view that includes other stakeholders. Two new perspectives that fit this broader view, customer value and shareholder value and relationship value are investigated and the implications of integrating a value orientation with a relationship marketing approach are discussed.

Investigation of the mixing flow structure in multilobe mixers

A computational procedure is described to study the mixing flow in a multilobe turbofan mixer. The predictions have been obtained using a finite volume method to solve the density-weighted time-averaged Navier-Stokes equations. Turbulence is characterized by the k-e eddy viscosity model. To fit the irregular boundaries of the flowfield, curvilinear nonorthogonal coordinates are employed. The robustness of the computational procedure is enhanced by making use of nonstaggered grids. In the calculation the computational domain contains not only the mixing duct but also the lobe itself. Three kinds of configuration are under consideration : a confluent mixer, a convoluted mixer, and a forced mixer. Results show that the streamwise vortex generated at the trailing edge is the most prominent flow structure for the forced mixer, responsible for the effective mixing. The strength of the streamwise vortex can be characterized by the circulation. A parameter termed mixedness is defined to describe the effects of the mixing process. In addition to the streamwise vortex, normal vortices are generated by the velocity difference in the shear layer between the core and fan streams.

Fixed geometry mixer/ejector suppression system for turbofan aircraft engines

An internal flow mixer is attached to the rearward end of a turbofan engine for inverting the engine fan and core streams. Rearwardly of the internal flow mixer is a multi-lobed exhaust nozzle which mixes ambient air with the gases flowing from the flow mixer. An ejector housing lined with acoustic absorption material receives the flow from the exhaust nozzle and discharges the thrust producing gases in noise abatement condition.

COMBUSTION OSCILLATIONS IN A TWIN-STREAM AFTERBURNER

In a modern turbo-fan engine, the afterburner flame-holders are positioned in the mixing flow between the core and bypass streams. These two streams have different velocities and temperatures. They also have different duct lengths and, therefore, different acoustic properties. The influence of such a twin-stream supply on acoustically coupled combustion oscillations is investigated in this paper. Measurements on an experimental rig show how differences in the acoustic impedances, the mean velocities and the mean temperatures in the two supply streams lead to appreciably different unsteady heat release rates in the two streams. These affect the frequency of the combustion oscillations. A theory explains these results and correctly describes the variation in frequency as the properties of the two supply streams are varied.

A Comparison of the Measured and Predicted Flow Field in a Modern Fan-Bypass Configuration

A three-dimensional viscous Navier–Stokes flow solver was used to predict core and bypass rotor performance and radial flow characteristics of a 4.6:1 bypass ratio, single-stage fan. The three-dimensional flow solver can handle several blade rows simultaneously and has the capability to include a downstream splitter. Results of the analysis are compared with experimental data obtained during rig testing of a modern high bypass single-stage turbofan in which rotor performance for both bypass and core streams was measured.

Ultrasonic probe tip

An ultrasonic probe tip is provided with improved characteristics for removing material during surgery on a cataract or the like, and reducing the removed material into smaller particles. The tip includes a body section and a cutting section with a passage extending through both sections. Aspiration is provided to the passage means through a collector passageway within a smooth, cylindrical head. An annular sharpened edge on the cutting section removes the material and emulsifies the particles. The cutting section is an enlarged chamber to receive a core stream of liquid from the operation site drawn into and defined by the smaller passage in the body section to generate vortex action clearing the operation site, reducing the size of the particles to prevent clogging and prevent cavitation. The interior surface of the enlarged chamber can be roughened, such as by etching, in order to provide additional emulsification action. The tip is fabricated of titanium and used on conventional ultrasonic handpieces.

Combustion studies of metallized fuels for solid-fuel ramjets

Combustion phenomena of highly metallized, boron containing, solid fuels in solid-fuel ramjets (SFRJ) were studied by means of high-speed photography using a windowed two-dimensional SFRJ combustor. The ex- periments indicated the existence of a gas-phase diffusion of the volatile fuel ingredients within the bound- ary layer above the fuel surface. It was also revealed that material is often emitted from the surface in the form of large pieces arid segments. Flow impingement on the surface may cause surface heating and glowing by chemical reactions, which promote the high-speed ejection of hot particles and the emittance and disintegration of large glowing segments and pieces from the fuel surface layer into the gas stream. HERMOCHEMICAL evaluation of fuel candidates for advanced solid-fuel ramjet (SFRJ) systems reveals the high energy and energy density of some metals, especially boron and boron compounds.1 Compared with the commonly used hydrocarbon (HC) fuels, boron exhibits remarkable theoretical heat of combustion per unit mass (about 30% higher than HCs) and per unit volume (almost three times that of HC). As an ingredient of solid fuels for ramjets, metals, in- cluding elemental boron or boron compounds (e.g., boron carbide), are usually introduced as fine powders into a matrix of polymeric material. In spite of the promising potential, the practical use of solid-fuel formulations highly loaded with metal particles can present severe problems associated with complex burning phenomena, which have major effects on the energy genera- tion process within the combustor and may lead to poor combustion efficiencies and low motor performance. Experimental investigations and modeling of the combus- tion of nonmetallized fuels in SFRJ combustors have pro- vided a good description of the main combustion and flow characteristics.2'3 See Fig. la. The foremost region of the combustor is characterized by a separated recirculation flow zone generated by the inlet step used for stabilization. Downstream of the reattachmeht zone, often along most of the fuel grain length, a gas-phase diffusion flame, typically a narrow flame sheet, is established within the turbulent boundary layer that develops over the condensed fuel sur- face.4 Fuel vapors diffuse from the decomposing fuel beneath the flame, while oxygen is transported to the from the core stream along the combustor centerline. Heat feedback from the to the condensed fuel determines the fuel regression rate and completes the combustion cycle. The situations encountered when using highly metallized fuels are somewhat different (Fig. Ib). Although the flow characteristics are similar to those existing in the combustor employing nonmetallized fuels, the combustion phenomena are not the same. Metal particles tend to accumulate and coalesce at the condensed fuel surface prior to their ejection into the gas stream. The result may be the formation of

Experimental Evaluation of Heavy Fan-High-Pressure Compressor Interaction in a Three-Shaft Engine: Part 1—Experimental Setup and Results

Severe aerodynamic interaction between the fan core stream section and the high-pressure compressor of a three-shaft low-bypass-ratio engine is described. At high fan running lines a heavy single-cell rotating stall was found in the fan core stream even at high aerodynamic speeds between 90–98%. The rotating circumferential distortion with 180–200 deg sector angle is swallowed by the intermediate pressure compressor but erodes the high-pressure compressor surge margin by about 22%, leading to steady-state surges. A remotely mounted transducer in a specific arrangement was used successfully for measurements in the hot environment behind intermediate and high-pressure compressor using a so-called “long-line” system with a closed end at the downstream pipe.

Performance estimation for turbofans with and without mixers

A relatively simple equation set is developed to estimate the optimal performance of mixed-stream turbofans with component losses included. The set provides the specific fuel consumption and required bypass flow and fan pressure ratios to give a prescribed specific thrust for given flight conditions, component design limits, and engine core stream Mach number entering the mixer. Example results confirm the expectation (based on ideal cycle analysis) that the optimal specific fuel consumption and bypass ratio are nearly independent of the fan pressure ratio, provided that an optimal mixer is employed. Further, an engine designed for use in a mixedstream configuration only would best use a lower fan pressure ratio than would an engine deliberately designed for an unmixed exhaust. a0 ec ec> et F / G h K M m p pt S S3> T

Investigation of mixing in a turbofan exhaust duct. II Computer codeapplication and verification

A three-dimensional analysis of turbofan forced mixer nozzle aerodynamics demonstrates that the complex flow structure is dominated by geometrically induced secondary flow rather than by turbulence. The test apparatus consisted of a fixed upstream model section and a rotating shroud. The Mach number of the fan and core streams at the mixing plane (lobe exit) was 0.45, the bypass ratio was about 4, and the Reynolds number based on the shroud radius was 1,100,000. The three velocity components near the exit plane of the lobes were measured using flow angularity probes to provide information about the mixer inflow conditions for turbulent computations. The validity of a previous computer code was demonstrated in a comparison of the nozzle exit temperature data with the computed temperature distributions. The mechanism most responsible for the generation of secondary flow within the lobes is due to the turning of the fan and core streams in opposite radial directions.

A numerical solution of the vertical boundary-layer equations in a horizontally heated porous cavity

A numerical scheme for the solution of the vertical boundary-layer equations in a two-dimensional horizontally heated cavity filled with a porous medium is described. A novel feature of the problem is that although the equations are parabolic, the core boundary conditions at the edge of the layer are not specified a priori. Instead the core stream function and temperature profiles must satisfy certain symmetry conditions requiring an iterative approach in the numerical scheme. The results confirm the possibility of the frequently assumed hypothesis in cavity flows that the vertical boundary layers empty into the core and thus complete the main flux circulation in the cavity. The numerical results are compared with both asymptotic and approximate solutions of the equations.

Part-Span Variable Inlet Guide Vanes for V/STOL Fan Thrust Modulation

Part-span, variable inlet guide vanes (VIGV's) have been proposed as a means of modulating thrust for attitude control of V/STOL aircraft systems. The utilization of these part-span VIGV's in subsonic aircraft system studies have shown significant payoffs in reducing weight and increasing performance of the engine core when used in conjunction with a means of power transfer from one fan to the other. The part-span VIGV's were tested on a TF34 engine at NASA Lewis under a joint NASA-Navy sponsorship to demonstrate the feasibility and performance of these proposed thrust modulating devices on an operational engine system. The results of the tests showed the VIGV's to be an effective thrust modulating device while maintaining core supercharging. The fan was mapped to stall for a range of speeds and VIGV settings. Fan tip performance (modulated by part-span VIGV's) and hub performance (unmodulated) are presented. Testing was repeated with a splitter extended between the core and bypass streams. The effects of distortion were reduced and less stall sensitivity was experienced with the inlet guide vanes (IGV's). At 0-deg IGV closure little effect was seen on fan or core compressor efficiency and measured specific fuel consumption (sfc). Test data indicate that thrust modulation of ±20% can readily be achieved by using part-span VIGV's.

Mach Reflection Associated with Over-Expanded Nozzle Free Jet Flows

The occurrence of Mach reflection within the over-expanded nozzle free jet flow has been examined. A flow model emphasizing the interaction between the outer and central core streams has been developed to deal with flow situations where detailed inviscid calculations of the flowfield with Mach reflexion are not possible. The results obtained show reasonably good agreement with the available experimental data. This method has also produced comparable results where detailed calculations of the flowfield are possible.

Production of Uniform Microspheres

A new technique has been developed for producing microspheres uniform in volume and fluorescence or radioactive tracer. Very uniform spheres with selected diameters are produced by introducing one liquid into the center of a moving stream of a second liquid (of differing surface tension) and breaking the core stream into uniform droplets by the action of a piezoelectric transducer. Fluorescent spheres of 10 μ diam have been produced having a coefficient of variation in volume and fluorescence as low as 3.6%. This corresponds to a diameter variation of about 1.5%.

Separation of gas mixture in an axisymmetric supersonic jet

The separation of gas mixture in an axially symmetric supersonic jet is investigated. The supersonic jet is separated into the peripheral stream and the core stream by a skimmer and the total diffusion flux of the lighter component into the peripheral stream is obtained. The experimental results are presented for the binary gas mixture of hydrogen and nitrogen. An approximate equation is proposed which gives the diffusion flux as a function of cut and Mach number. The experimental results were in fairly good agreement with the results of calculation by the proposed equation.