Uniform Inlet Temperature Research Articles

Investigation of Tonal Noise in a High Pressure Turbine Stage Due to Temperature Inhomogeneous of the Inflow

The tonal sound emission of a high pressure turbine stage due to total temperature inhomogeneous of the inflow investigated numerically. A non-uniform mean temperature made by a result of the discrete burners inside the annular combustion chamber. In present paper we made a setting that 14 periodic total temperature distribution in the azimuthal direction in the turbine inlet. Through comparison between non-uniform inlet temperature case and uniform inlet temperature case, the results show that the sound power emitted in the downstream direction is increased by 5.9 dB at the blade-passing frequency and by remarkably 11.6 dB at the first harmonic of the blade-passing frequency. This result indicated the total temperature fluctuation in the inlet of turbine stage would affect the sound field drastically.

Heat Transfer for the Blade of a Cooled Stage and One-Half High-Pressure Turbine—Part I: Influence of Cooling Variation

Heat-flux measurements are presented for a one-and-one-half stage high-pressure turbine operating at design-corrected conditions with modulated cooling flows in the presence of different inlet temperature profiles. Coolant is supplied from a heavily film-cooled vane and the purge cavity (between the rotor disk and the upstream vane) but not from the rotor blades, which are solid metal. Thin-film heat-flux gauges are located on the uncooled blade pressure and suction surface (at multiple span locations), on the blade tip, on the blade platform, and on the disk and vane sides of the purge cavity. These measurements provide a comprehensive picture of the effect of varying cooling flow rates on surface heat transfer to the turbine blade for uniform and radial inlet temperature profiles. Part I of this paper examines the macroscopic influence of varying all cooling flows together, while Part II investigates the individual regions of influence of the vane outer and purge cooling circuits in more detail. The heat-flux gauges are able to track the cooling flow over the suction surface of the airfoil as it wraps upwards along the base of the airfoil for the uniform vane inlet temperature profile. A similar comparison for the radial profile shows the same coolant behavior but with less pronounced changes. From these comparisons, it is clear that cooling impacts each temperature profile similarly. Nearly all of the cooling influence is limited to the blade suction surface, but small changes are observed for the pressure surface. In addition to the cooling study, a novel method of calculating the adiabatic wall temperature is demonstrated. The derived adiabatic wall temperature distribution shows very similar trends to the Stanton number distribution on the blade.

Aerodynamics and Heat Transfer for a Cooled One and One-Half Stage High-Pressure Turbine–Part II: Influence of Inlet Temperature Profile on Blade Row and Shroud

Heat flux measurements are presented for the uncooled blades of a one and one-half stage turbine operating at design corrected conditions with a fully cooled upstream vane row and with rotor disk cavity purge flow. This paper highlights the differences in blade heat flux and temperature caused by uniform, radial, and hot streak inlet temperature profiles. A general discussion of temperature profile migration is provided in Part I, and Part III presents data for hot streak magnitudes and alignments. The heat flux and fluid temperature measurements for the blade airfoil, platform, angel wing (near the root), and tip as well as for the stationary outer shroud are influenced by the vane inlet temperature profile. The inlet temperature profile shape can be clearly observed in the blade Stanton number measurements, with the radial and hot streak profiles showing a greater redistribution of energy than the uniform case due to secondary flows. Hot-gas segregation is observed to increase with the strength of the temperature distortion. Measurements for the hot streak profile show a segregation of higher temperature fluid to the pressure surface when compared with a uniform profile. The introduction of vane and purge cooling is found to further accentuate the flow segregation due to coolant migration to the suction surface.

Aerodynamics and Heat Transfer for a Cooled One and One-Half Stage High-Pressure Turbine—Part I: Vane Inlet Temperature Profile Generation and Migration

As controlled laboratory experiments using full-stage turbines are expanded to replicate more of the complicated flow features associated with real engines, it is important to understand the influence of the vane inlet temperature profile on the high-pressure vane and blade heat transfer as well as its interaction with film cooling. The temperature distribution of the incoming fluid governs not only the input conditions to the boundary layer but also the overall fluid migration. Both of these mechanisms have a strong influence on surface heat flux and therefore component life predictions. To better understand the role of the inlet temperature profile, an electrically heated combustor emulator capable of generating uniform, radial, or hot streak temperature profiles at the high-pressure turbine vane inlet has been designed, constructed, and operated over a wide range of conditions. The device is shown to introduce a negligible pressure distortion while generating the inlet temperature conditions for a stage-and-a-half turbine operating at design-corrected conditions. For the measurements described here, the vane is fully cooled and the rotor purge flow is active, but the blades are uncooled. Detailed temperature measurements are obtained at rake locations upstream and downstream of the turbine stage as well as at the leading edge and platform of the blade in order to characterize the inlet temperature profile and its migration. The use of miniature butt-welded thermocouples at the leading edge and on the platform (protruding into the flow) on a rotating blade is a novel method of mapping a temperature profile. These measurements show that the reduction in fluid temperature due to cooling is similar in magnitude for both uniform and radial vane inlet temperature profiles.

Developments in Hot-Streak Simulators for Turbine Testing

The importance of understanding the impact of hot-streaks, and temperature distortion in general, on the high pressure turbine is widely appreciated, although it is still generally the case that turbines are designed for uniform inlet temperature—often the predicted peak gas temperature. This is because there is an insufficiency of reliable experimental data both from operating combustors and from rotating turbine experiments in which a combustor representative inlet temperature profile has accurately been simulated. There is increasing interest, therefore, in experiments that attempt to address this deficiency. Combustor (hot-streak) simulators have been implemented in six rotating turbine test facilities for the study of the effects on turbine life, heat transfer, aerodynamics, blade forcing, and efficiency. Three methods have been used to simulate the temperature profile: (a) the use of foreign gas to simulate the density gradients that arise due to temperature differences, (b) heat exchanger temperature distortion generators, and (c) cold gas injection temperature distortion generators. Since 2004 three significant new temperature distortion generators have been commissioned, and this points to the current interest in the field. The three new distortion generators are very different in design. The generator designs are reviewed, and the temperature profiles that were measured are compared in the context of the available data from combustors, which are also collected. A universally accepted terminology for referring to and quantifying temperature distortion in turbines has so far not developed, and this has led to a certain amount of confusion regarding definitions and terminology, both of which have proliferated. A simple means of comparing profiles is adopted in the paper and is a possible candidate for future use. New whole-field combustor measurements are presented, and the design of an advanced simulator, which has recently been commissioned to simulate both radial and circumferential temperature nonuniformity profiles in the QinetiQ/Oxford Isentropic Light Piston Turbine Test Facility, is presented.

Performance evaluation of mixed convection in an inclined square channel with uniform temperature walls

Numerical analyses were performed for the effect of inclined angle on the mixing flow in a square channel with uniform temperature walls ( T w = 30 °C) and inlet temperature ( T 0 = 10 °C). Three-dimensional governing equations were solved numerically for Re = 100, Pr = 0.72 and various inclined angles (from −90° to 90°). Three-dimensional behavior of fluid in a channel was examined for each angle. Thermal performance was evaluated using the relationship between Nusselt number ratio and pressure loss ratio with and without buoyancy induced flow as a parameter of inclined angles. High heat transfer and low pressure loss region was from −15° to −60° in thermal performance using mean Nusselt number ratio.

Attributes of a derived differential/difference energy equation within the platform of the L�v�que problem

The main idea of the Leveque approximation was to provide a simple asymptotic solution for the development of the thermal boundary layer in a laminar tube flow with fully established velocity and uniform inlet temperature. Inspired in the “flat plate passage” idealization, Leveque assumed that the hydrodynamic boundary layer was confined to a thin annular region near the wall so that the velocity varied linearly with the distance y = R - r measured from the wall in an equivalent “parallel-plate passage”. In contrast, this paper addresses the Leveque problem adhering to the original energy conservation equation in cylindrical coordinates continually, but without making any geometric and/or hydrodynamic assumptions a priori. The semi-analytic solution procedure proposed here combines the Transversal Method Of Lines (TMOL) with the Frobenius method, a particular case of the power series method.

The Effect of Hot-Streaks on HP Vane Surface and Endwall Heat Transfer: An Experimental and Numerical Study

Pronounced nonuniformities in combustor exit flow temperature (hot-streaks), which arise because of discrete injection of fuel and dilution air jets within the combustor and because of endwall cooling flows, affect both component life and aerodynamics. Because it is very difficult to quantitatively predict the effects of these temperature nonuniformities on the heat transfer rates, designers are forced to budget for hot-streaks in the cooling system design process. Consequently, components are designed for higher working temperatures than the mass-mean gas temperature, and this imposes a significant overall performance penalty. An inadequate cooling budget can lead to reduced component life. An improved understanding of hot-streak migration physics, or robust correlations based on reliable experimental data, would help designers minimize the overhead on cooling flow that is currently a necessity. A number of recent research projects sponsored by a range of industrial gas turbine and aero-engine manufacturers attest to the growing interest in hot-streak physics. This paper presents measurements of surface and endwall heat transfer rate for a high-pressure (HP) nozzle guide vane (NGV) operating as part of a full HP turbine stage in an annular transonic rotating turbine facility. Measurements were conducted with both uniform stage inlet temperature and with two nonuniform temperature profiles. The temperature profiles were nondimensionally similar to profiles measured in an engine. A difference of one-half of an NGV pitch in the circumferential (clocking) position of the hot-streak with respect to the NGV was used to investigate the affect of clocking on the vane surface and endwall heat transfer rate. The vane surface pressure distributions, and the results of a flow-visualization study, which are also given, are used to aid interpretation of the results. The results are compared to two-dimensional predictions conducted using two different boundary layer methods. Experiments were conducted in the Isentropic Light Piston Facility (ILPF) at QinetiQ Farnborough, a short-duration engine-sized turbine facility. Mach number, Reynolds number, and gas-to-wall temperature ratios were correctly modeled. It is believed that the heat transfer measurements presented in this paper are the first of their kind.

Assessment of the local thermal non-equilibrium condition in developing forced convection flows through fluid-saturated porous tubes

The present investigation is concerned with the numerical simulation of forced convection heat transfer flows in a tube filled with a fluid-saturated porous medium. Steady state incompressible flows with isothermal tube walls are considered along with a uniform inlet approach velocity and temperature conditions. In addition, the generalized form of the momentum equation is considered by accounting for the solid boundary and the Forchheimer quadratic inertial effects without invoking the boundary layer approximations. Moreover, the energy transport is simulated using the two-equation model, which accounts separately for the local fluid and solid temperatures. The numerical solution is obtained through the application of the finite volume method. The validity of the local thermal equilibrium (LTE) was tested over a wide domain of the employed dimensionless parameters, namely; the Peclet number, Biot-like number, effective fluid-to-solid thermal conductivity ratio, Reynolds number, Forchheimer dimensionless coefficient and Darcy number. The validity of the LTE condition was examined for the full tube length and upon excluding the first tube diameter length.

Performance Evaluation of Mixed Convection in an Inclined Square Channel with Uniform Temperature Walls

Abstract Numerical analyses were performed for the effect of inclined angle on the mixing flow in a square channel with uniform temperature walls (Tw = 30 °C) and inlet temperature (T0 = 10 °C). Three-dimensional governing equations were solved numerically for Re = 100, Pr = 0.72 and various inclined angles (from −90° to 90°). Three-dimensional behavior of fluid in a channel was examined for each angle. Thermal performance was evaluated using the relationship between Nusselt number ratio and pressure loss ratio with and without buoyancy induced flow as a parameter of inclined angles. High heat transfer and low pressure loss region was from −15° to −60° in thermal performance using mean Nusselt number ratio.

Heat transfer measurements on an intermediate-pressure nozzle guide vane tested in a rotating annular turbine facility, and the modifying effects of a non-uniform inlet temperature profile

In modern gas turbine engines there exist significant temperature gradients in the combustor exit flow. These gradients arise because both fuel and dilution air are introduced within the combustor as discrete jets. The effects of this non-uniform temperature field on the aerodynamics and heat transfer rate distributions of nozzle guide vanes and turbine blades is difficult to predict, although an increased understanding of the effects of temperature gradients would enhance the accuracy of estimates of turbine component life and efficiency. Low-frequency measurements of heat transfer rate have been conducted on an annular transonic intermediate-pressure (IP) nozzle guide vane operating downstream of a high-pressure (HP) rotating turbine stage. Measurements were conducted with both uniform and non-uniform inlet temperature profiles. The non-uniform temperature profile included both radial and circumferential gradients of temperature. Experiments were conducted in the isentropic light piston facility at QinetiQ Pyestock, a short-duration engine-size turbine facility with 1.5 turbine stages, in which Mach number, Reynolds number and gas—wall temperature ratios are correctly modelled. Experimental heat transfer results are compared with predictions performed using boundary layer methods.

THE NUSSELT NUMBER AND FRICTION FACTOR AT THE ENTRANCE OF A MICRO-DUCT

Expressions are presented for the Nusselt number and friction factor at the entrance of a micro-duct with uniform inlet velocity and temperature profiles and for the gas flow and heat transfer in the velocity-slip and temperature-jump regime. The entrance Nusselt number and friction factor are shown to be of finite values, and they are dependent on the Knudsen number and gas-wall accommodation factors but independent of the geometrical form of duct section

COMBINED CONVECTION AND RADIATION IN SIMULTANEOUSLY DEVELOPING FLOW AND HEAT TRANSFER WITH NONGRAY GAS MIXTURES

Abstract Combined convection and radiation in simultaneously developing laminar flow and heat transfer in a smooth tube is numerically considered with the P-I approximation and the exponential wideband model. The fluid is a mixture of carbon dioxide, water vapor, and nitrogen, The bulk mean temperature variation, temperature profiles, and Nusselt numbers are shown for a uniform inlet temperature and several constant wall temperatures. Nusselt numbers for simultaneously developing flow are compared with those for thermally developing flow. The effects of the mole fraction of the nongray gases and the wall emissivity on convective and radiative Nusselt numbers are explored.

Development of three-dimensional, streamwise-periodic flows in mixed-convection heat transfer

The three-dimensional, parabolized form of the coupled equations of motion and energy are solved to study the development of mixed-convection heat transfer in the entrance region of horizontal square ducts. The specific problem considered here is that of axially uniform heat flux and peripherally uniform temperature with parabolic inlet profile and uniform inlet temperature in a square cross-section. Previous studies have been confined mostly to two-dimensional flows in the fully developed region. Recent two-dimensional calculations have indicated the existence of multiple steady-state solutions in the fully developed region with two- and four-cell flow structure. Present three-dimensional calculations, carried over the whole entrance length and the full cross-section, indicate the evolutionary path that lead to such two-dimensional flows. Furthermore they shed new light on the nature of flows in regions where all known two-dimensional solutions become unstable in some manner. For low Grashof numbers and Pr = 0.73 the secondary velocities develop into an axially invariant state with two counter-rotating vortices. For Grashof numbers above 2.2 × 105 the inlet profiles evolve into a state with a four-cell secondary flow structure. As in a related problem of flow in a curved channel (Winters 1987; Bara et al. 1992), the two-dimensional, four-cell solutions are found to be unstable to asymmetric perturbations. Such perturbations trigger a new, streamwise-periodic mode which is sustained over long lengths in the flow direction. For Grashof numbers above 5.6 × 105 axially invariant two-cell solutions reappear. Some of the three-dimensional solutions corresponding to the streamwise periodic mode lack the reflective symmetry about the vertical centreline and hence these flows occur with multiplicity of two.

Mixed convection analysis in large baffled rectangular chambers with internal heat sources

An investigation to determine the effects of mixed convection on the flow structure of large baffled chambers with internal heat sources has been completed. Baffles and internal heat sources are placed symmetrically about the vertical axis while maintaining a constant and uniform inlet velocity, inlet temperature, and wall temperature. Time-dependent experimental and two-dimensional numerical results are compared at various chamber locations to demonstrate the transition of the flow structure through a sequence of bifurcations with increasing internal heat source temperatures.

Laminar Forced-Convective Heat Transfer with Varying Properties in the Entrance Region of Flat Rectangular Ducts

Numerical results for air undergoing laminar forced-convective heat transfer in the entrance region of a flat rectangular duct with uniform wall temperature are obtained for Uniform inlet velocity and temperature profiles. The coupled governing partial differential equal ions are solved in discretized form with property variations being updated through physical property relations. This enables the physical property and thermofluid solutions to converge simultaneously, resulting in a realistic solution to the governing equations. Constant-property results are also obtained, and Nusselt numbers of both the constant-and variable-property models are compared with those of other numerical computations. The results of the variable-property model are also compared with available experimental data. The variable-property results exhibit excellent correlation with the available experimental data. A sensitivity analysis is performed to determine the effects of individual property variations on local Nusselt numbers.

Forced convection heat transfer to a power‐law fluid in arbitrary cross‐section ducts

AbstractA numerical method is developed to predict the three‐dimensional forced convection laminar incompressible flow of a power law fluid in arbitrary cross‐section straight ducts. The continuity equation and boundary layer forms of the energy and momentum equations in rectangular coordinates are transformed into new orthogonal coordinates with boundaries coinciding with the coordinate surfaces. The resulting equations are solved using the finite difference technique.The numerical scheme is capable of handling different hydrodynamic and thermal entry boundary conditions but results are only presented for uniform inlet velocity and temperature profiles and isothermal wall.To demonstrate the wider applicability of the method local heat transfer coefficients and pressure drop in square, trapezoidal and regular pentagonal ducts are computed as functions of pertinent thermal and hydrodynamic parameters.

Laminar Flow and Heat Transfer to a Non-Newtonian Fluid in an Entrance Region of a Square Duct with Prescribed Constant Axial Wall Heat Flux

Abstract Forced-convection heat transfer information as a function of the pertinent nondimensional numbers is obtained numerically for laminar incompressible non-Newtonian fluid flow in the entrance region of a square duct with simultaneously developing temperature and velocity profiles for constant axial wall heat flux with uniform peripheral wall temperature. The power-law model characterizes the non-Newtonian behavior. Finite-difference representations are developed for the equations of the mathematical model, and numerical solutions are obtained assuming uniform inlet velocity and temperature distributions. Results are presented for local and mean Nusselt numbers as functions of the Graetz number and the Prandtl number in the entrance region. Comparisons are made with previous analytical work for Newtonian fluids. The results show a strong effect of the Prandtl number on the Nusselt numbers with fully developed and uniform velocity profiles representing the lower and upper limits, respectively. The re...

LAMINAR FLOW AND HEAT TRANSFER TO A NON-NEWTONIAN FLUID IN AN ENTRANCE REGION OF A SQUARE DUCT WITH PRESCRIBED CONSTANT AXIAL WALL HEAT FLUX

Abstract Forced-convection heat transfer information as a function of the pertinent nondimensional numbers is obtained numerically for laminar incompressible non-Newtonian fluid flow in the entrance region of a square duct with simultaneously developing temperature and velocity profiles for constant axial wall heat flux with uniform peripheral wall temperature. The power-law model characterizes the non-Newtonian behavior. Finite-difference representations are developed for the equations of the mathematical model, and numerical solutions are obtained assuming uniform inlet velocity and temperature distributions. Results are presented for local and mean Nusselt numbers as functions of the Graetz number and the Prandtl number in the entrance region. Comparisons are made with previous analytical work for Newtonian fluids. The results show a strong effect of the Prandtl number on the Nusselt numbers with fully developed and uniform velocity profiles representing the lower and upper limits, respectively. The re...