Unsteady Aerodynamic Measurements Research Articles

Understanding Thermal Unsteadiness in Engine Representative Flows and Improved Methodologies for Derived Heat Transfer Calculations Using Thin-Film Gauges

Abstract The Oxford Turbine Research Facility (OTRF) is a high-speed rotating transient test facility, which allows unsteady aerodynamic and heat transfer measurements at engine representative conditions. In addition, a variety of inlet temperature profiles can be simulated in the rig including radial distortion, circumferential distortion, and swirl. However, the engine representative flows cause complications in the processing of heat transfer data. The unsteadiness in temperature data was found to significantly rise as temperature distortions were introduced in the nozzle guide vane (NGV) inlet profile, to model a lean-burn combustor exit. Using the NGV inlet temperature profile survey data, the thermal unsteadiness has been quantified and compared with a uniform inlet. The experiments with a radially varying NGV inlet temperature profile showed up to nine times higher thermal unsteadiness, compared to the uniform inlet. The second part of the paper is a continuation of the work presented in a previous paper by Singh et al. and describes improved methodologies for derived heat transfer calculations using thin-film gauges. In addition, the uncertainty associated with the derived heat transfer parameters, such as the heat transfer coefficient and adiabatic wall temperature has been quantified. The refined processing techniques have been demonstrated on casing heat transfer measurements, acquired in the OTRF with two inlet temperature profiles.

Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation

Abstract The first part of the paper presents commissioning of a single-stage high-pressure (HP) turbine employed in a series of extensive experiments to study the aerodynamics and heat transfer on the rotor surface and casing liner. The Oxford Turbine Research Facility (OTRF), a high-speed rotating transient test facility has the capability to take unsteady aerodynamic and heat transfer measurements at engine representative conditions with a variety of inlet temperature profiles including radial distortion and swirl. A temperature profile survey was conducted at the inlet of the HP nozzle guide vane (NGV). Static and total pressure and temperature measurements have been taken at various locations on the rig including NGV surface, inlet and exit, and rotor exit to establish rig operating conditions. Detailed description of mass flow rate measurements along with calculation of heat loss factor in the rig is presented. The second part of the paper presents a parametric study performed to improve heat transfer measurement calculations from high-frequency response thin-film gauges. The effect of parameters like material properties and thickness of substrate on heat flux has been studied. A detailed uncertainty analysis for heat flux is also presented. A thermal model calibrated with analytical solutions has been developed to optimize thin-film gauge configurations and to study side-conduction effects.

A Novel MEMS-Based Probe for Unsteady Aerodynamic Measurements: A Proof-of-Concept Study

A novel MEMS-based probe is described which is capable of measuring unsteady flow angles, total pressure and velocity. Uniquely, this probe uses shear stress sensors to relate the surface streamline directions on the probe face to the freestream flow angles. The probe has the potential to be miniaturised to around 1mm in diameter and achieve a temporal resolution of up to several 100kHz. A computational study of virtual calibrations is used to understand how to adjust the probe geometry and sensor locations to maximise the sensitivity and range of the device. The most promising configuration was calibrated experimentally using a large-scale probe to demonstrate the feasibility of the concept.

Computational and Experimental Study of Hot Streak Transport Within the First Stage of a Gas Turbine

Abstract The paper discusses the migration, the interaction with the blades, and the attenuation of hot streaks generated by combustor burners, during their propagation within the first turbine stage of aero-engines. Experiments and computational fluid dynamics (CFD) simulations were carried out in the framework of the European Project RECORD and on its follow-up. Measurements considering burner-representative temperature perturbations injected upstream of an un-cooled high-pressure gas turbine stage were performed in the high-speed closed-loop test-rig of the Politecnico di Milano (Italy). The hot streaks were injected in a streamwise direction at the stage inlet in four different circumferential positions with respect to the stator blade. They feature a 20% over-temperature with respect to the main flow. Detailed temperature measurements as well as unsteady aerodynamic measurements upstream and downstream of the blade rows were performed. Time-accurate CFD simulations of the flow upstream and within the turbine stage were performed with the TRAF code, developed by the Università degli Studi di Firenze (Italy). Measurements show a relevant attenuation of hot streaks throughout their transport within the stator and the rotor blade rows, highly depending on the injection azimuthal position. The perturbations were observed to lose their spatial coherence, especially in the transport within the rotor, and to undergo severe spanwise migration. Simulations exhibit a good agreement with the experiments on the measurement planes and allow tracking the complex flow phenomena occurring within the blade rows. Finally, the aerodynamic and thermal implications of the inlet temperature perturbations are properly highlighted and discussed.

Pressure tap cavity for unsteady aerodynamic pressure measurements

Extensive laboratory experiments were carried out to investigate the effect of a cavity behind the pressure tap on unsteady aerodynamic pressure measurements. The volume of the studied cavity (truncated cone) is 1.5 mm3 behind the pressure tap (cylinder) of 1 mm3 and the studied frequency range is up to 256 Hz. This design with a cavity behind the pressure tap and the studied frequency range are common for a wide range of mechanical, civil, aerospace, and environmental engineering applications. The experiments were performed using three different facilities, i.e. a signal generator, a low-turbulence wind tunnel, and a high-turbulence wind tunnel. Conclusions were made based on the quantitative analysis of the peak amplitude and frequency of the amplitude spectral density of pressure fluctuations as well as on the standard deviation of pressure fluctuations. Results were qualitatively analyzed with respect to phase shifts and amplitude deviations. The results clearly indicate that a 2.5 mm3 cavity with a pressure tap is suitable for unsteady pressure measurements in the frequency range up to 256 Hz as the phase shift and amplitude deviation of the unsteady pressure signal in those conditions proved to be negligible.

A Parametric Study of the Blade Row Interaction in a High Pressure Turbine Stage

An extensive experimental analysis on the subject of the unsteady periodic flow in a high subsonic high pressure (HP) turbine stage has been carried out at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy). In this paper the aerodynamic blade row interaction in HP turbines, enforced by increasing the stator and rotor blade loading and by reducing the stator-rotor axial gap, is studied in detail. The time-averaged three-dimensional flowfield in the stator-rotor gap was investigated by means of a conventional five-hole probe for the nominal (0 deg) and highly positive (+22 deg) stator incidences. The evolution of the viscous flow structures downstream of the stator is presented to characterize the rotor incoming flow. The blade row interaction was evaluated on the basis of unsteady aerodynamic measurements at the rotor exit, performed with a fast-response aerodynamic pressure probe. Results show a strong dependence of the time-averaged and phase-resolved flowfield and of the stage performance on the stator incidence. The structure of the vortex-blade interaction changes significantly as the magnitude of the rotor-inlet vortices increases, and very different residual traces of the stator secondary flows are found downstream of the rotor. On the contrary, the increase in rotor loading enhances the unsteadiness in the rotor secondary flows but has a little effect on the vortex-vortex interaction. For the large axial gap, a reduction of stator-related effects at the rotor exit is encountered when the stator incidence is increased as a result of the different mixing rate within the cascade gap.

V-Tail Stalling at Combined Angles of Attack and Sideslip

References 1Sakell, L., and Knight, D. D. (eds.), Proceedings of the First AFOSR Conference on Dynamic Motion Computational Fluid Dynamics, Rutgers Univ., New Brunswick, NJ, 1996. 2Baysal, O., Singh, K. P., and Yen, G.-W., “Dynamic CFD Methods for Prescribed and Aerodynamically-Determined Relative-Moving Multibody Problems,”Proceedings of theFirst AFOSRConference on DynamicMotion CFD, edited by L. Sakell and D. Knight, Rutgers Univ., New Brunswick, NJ, 1996, pp. 31–44. 3Singh, K. P., and Baysal, O., “3D Unstructured Method for Flows Past Bodies in 6-DOF Relative Motion,” Proceedings of 6th International Symposium on CFD, edited by M. Hafez, Vol. 3, Univ. of California, Davis, CA, 1995, pp. 1161–1168. 4Singh,K. P., Newman, J. C., III, and Baysal, O., “Dynamic Unstructured Method for Flows Past MultipleObjects in RelativeMotion,”AIAA Journal, Vol. 33, No. 4, 1995, pp. 641–659. 5Rausch, V. L., McClinton, C. R., and Hicks, J. W., “Scramjets Breathe New Life into Hypersonics,” Aerospace America, Vol. 35, No. 7, 1997, pp. 40–46. 6Batina, J. T., “Unsteady Euler Airfoil SolutionsUsing Unstructured Dynamic Meshes,” AIAA Paper 89-0115, Jan. 1989. 7Baysal, O., “Flow Analysis and Design Optimization Methods for Nozzle-Afterbody of a Hypersonic Vehicle,” Computational Methods in Hypersonic Aerodynamics, Kluwer, Dordrecht, The Netherlands, 1992, pp. 341–386. 8Baysal, O., and Luo, X.-B., “Computational Aeromechanics Method with Multigrid Accelerated Dual Time Stepping on Unstructured Meshes,” Proceedings of American Society ofMechanicalEngineers FluidsEngineering Division Summer Meeting, American Society of Mechanical Engineers, New York, FEDSM-98-4939, 1998. 9Baysal, O., and Luo, X.-B., “Staging of a Hypersonic Vehicle: Numerical Simulations Using Dynamic Unstructured Meshes,” Proceedings of 16th AIAA Applied AerodynamicsConference, Reston, VA, 1998, pp. 85– 95. 10Pirzadeh,S., “Recent Progress inUnstructuredGridGeneration,”AIAA Paper 92-0445, Jan. 1992. 11Hanel, D., Schwane, R., and Seider, G., “On the Accuracy of Upwind Schemes for the Solution of the Navier–Stokes Equations,” AIAA Paper 87-1005, Jan. 1987. 12Landon, R., “NACA 0012 Oscillatory and Transient Pitching,” Compendium of Unsteady Aerodynamic Measurements, AGARD Rept. 702, 1982, pp. 3.3–3.25. V-Tail Stalling at Combined Angles of Attack and Sideslip

Unsteady aerodynamic force measurements on a super-tall building with a tapered cross section

The unsteady wind loads acting on a super-tall building with a tapered cross section and beveled corners were measured as functions of reduced velocity and motion amplitude. The model amplitude was controlled by an hydraulic actuator and the unsteady sectional aerodynamic loads were measured using manifolded pressure taps. The damping components of the along-wind and cross-wind unsteady aerodynamic forces were obtained from the time histories of fluctuating aerodynamic force. The vertical distribution of damping component dependent on amplitude and reduced frequency are discussed. The obtained aeroelastic damping is compared with those from aeroelastic response measurement and those predicted by quasi-steady theory.

Unsteady Three-Dimensional Flow in a Single-Stage Transonic Fan: Part II—Unsteady Stator Exit Flow Field

Detailed unsteady aerodynamic measurements have been taken in a single-stage transonic fan with a very high stage-hub loading. Two-dimensional dynamic yawmeter probes, capable of measuring mean levels and fluctuations in stagnation pressure, static pressure, and yaw angle have been traversed at rotor exit and downstream of the stator, along with several types of pneumatic three-dimensional probe. Part I describes measurements taken at rotor exit. This paper, Part II, describes measurements taken at stator exit when the fan was operating at near-peak efficiency, on the design speed characteristic. The measurements indicate the effects of Rotor-Stator interaction on the development of the viscous endwall-corner flows at the hub and casing. In addition, they illustrate that significant changes in stagnation pressure level occur within much of the stator exit flow field during the rotor passing cycle.

Unsteady Three-Dimensional Flow in a Single-Stage Transonic Fan: Part I—Unsteady Rotor Exit Flow Field

Detailed unsteady aerodynamic measurements have been taken in a single-stage transonic fan with a very high stator-hub loading. Two-dimensional dynamic yawmeter probes, capable of measuring mean and fluctuating levels of stagnation pressure, static pressure, and yaw angle have been traversed at rotor exit, and downstream of the stator along with several types of pneumatic three-dimensional probe. Part I of this paper describes the dynamic yawmeters and their performance, and presents ensemble-averaged stagnation pressure and random stagnation pressure unsteadiness measurements taken at rotor exit. These are used to illustrate the salient features of the rotor flow field, and the effects of compressor aerodynamic loading. Part II presents measurements taken at stator exit.

Combination probe for hi-frequency unsteady aerodynamic measurements

A combination probe for time-resolved measurements of unsteady compressible flows in transonic wind tunnels is described. The probe measures stagnation (total) temperature and pressure, static pressure, and flow angles in two planes. From these, the fluctuating mass flux, Mach number, and velocity, as well as their components in three directions, can be deduced. The combination probe consists of a dual hot-wire aspirating temperature and pressure probe mounted piggyback with a high-frequency angle probe. The angle probe has four surface-mounted silicon pressure sensors. A scheme for retrieving from the four pressure signals the stagnation and static pressures. Mach number, and flow angles in two planes, is described. The calibrations forming the base for this procedure, obtained from steady-state tests, are given. Typical data obtained in the Karman vortex street shed from a cylinder and at the exit of a Mach 0.4 air jet are presented. >

Unsteady Aerodynamic Measurements on a Rotating Compressor Blade Row at Low Mach Number

An experiment was conducted on a heavily instrumented isolated model compressor rotor to study the unsteady aerodynamic response of the blade row to a controlled pitching oscillation of all blades in an undistorted flow, and to a circumferential inlet flow distortion with nonoscillating blades. To accomplish this, miniature pressure transducers were embedded in the blades and the unsteady pressure time histories were recorded. Both phases of the experiment were performed over a wide range of flow coefficient, from Cx/Um = 0.6 to 0.95 in 0.05 steps, and data were taken at each condition for sinusoidal disturbances characterized by one, two, and four per revolution waves. Steady-state data were acquired for flow coefficients from 0.55 to 0.99 in 0.05 steps. In this paper the steady and unsteady results of the portion of this experiment dealing with oscillating blades are compared with analytical predictions, and the steady results are compared with experimental data from previous work. Although the model blades were instrumented at five spanwise stations, only the midspan measurements will be presented herein. The measured pressures for nonoscillating blades were in good agreement with the steady potential flow predictions (and with previous steady experimental data) when the measured exit angle was imposed as the downstream boundary condition for the analysis. It was found that a quasi-steady approach yielded marginally acceptable agreement with the experimental results for the lowest frequency tested. For the higher reduced frequencies, the experimental data could not be modeled in this manner. In contrast, a comparison of the measurements with the Verdon–Caspar unsteady potential flow theory produced generally good agreement except near the leading edge at high mean incidence (i.e., at low flow coefficient). At high incidence the blades in this experiment had very high steady pressure gradients near the leading edge and it is suspected that this may be responsible for the lack of agreement. The agreement was somewhat better at the higher frequencies.