Michel Mansour

Full-Scale Wind Turbine Near-Wake Measurements Using an Instrumented Uninhabited Aerial Vehicle

In this paper, the first-ever measurements of the wake of a full-scale wind turbine using an instrumented uninhabited aerial vehicle (UAV) are reported. The key enabler for this novel measurement approach is the integration of fast response aerodynamic probe technology with miniaturized hardware and software for UAVs that enable autonomous UAV operation. The measurements, made to support the development of advanced wind simulation tools, are made in the near-wake (0.5D–3D, where D is rotor diameter) region of a 2 MW wind turbine that is located in a topography of complex terrain and varied vegetation. Downwind of the wind turbine, profiles of the wind speed show that there is strong three-dimensional shear in the near-wake flow. Along the centerline of the wake, the deficit in wind speed is a consequence of wakes from the rotor, nacelle, and tower. By comparison with the profiles away from the centerline, the shadowing effects of nacelle and tower diminish downstream of 2.5D. Away from the centerline, the deficit in wind speed is approximately constant ≈ 25%. However, along the centerline, the deficit is ≈ 65% near to the rotor, 0.5D–1.75D, and only decreases to ≈ 25% downstream of 2.5D.

Seven-Sensor Fast-Response Probe for Full-Scale Wind Turbine Flowfield Measurements

The unsteady wind profile in the atmospheric boundary layer upstream of a modern wind turbine is measured. The measurements are accomplished using a novel measurement approach that is comprised of an autonomous uninhabited aerial vehicle (UAV) that is equipped with a seven-sensor fast-response aerodynamic probe (F7S-UAV). The autonomous UAV enables high spatial resolution (∼6.3% of rotor diameter) measurements, which hitherto have not been accomplished around full-scale wind turbines. The F7S-UAV probe developed at ETH Zurich is the key-enabling technology for the measurements. The time-averaged wind profile from the F7S-UAV probe is found to be in very good agreement to an independently measured profile using the UAV. This time-averaged profile, which is measured in moderately complex terrain, differs by as much as 30% from the wind profile that is extrapolated from a logarithmic height formula; therefore, the limited utility of extrapolated profiles, which are commonly used in site assessments, is made evident. The time-varying wind profiles show that at a given height, the velocity fluctuations can be as much as 44% of the time-averaged velocity, therefore indicating that there are substantial loads that may impact the fatigue life of the wind turbine’s components. Furthermore, the shear in the velocity profile also subjects the fixed pitch blade to varying incidences and loading. Analysis of the associated velocity triangles indicates that the sectional lift coefficient at midspan of this modern turbine would vary by 12% in the measured time-averaged wind profile. These variations must be accounted in the structural design of the blades. Thus, the measurements of the unsteady wind profile accomplished with this novel measurement system demonstrate that it is a cost effective complement to the suite of available site assessment measurement tools.

Time-resolved entropy measurements using a fast response entropy probe

This paper describes a recently developed miniature fast response entropy probe and its application in the turbomachinery facilities at ETH Zurich. The development of the probe is motivated by the need to more clearly document the loss generation mechanisms in the harsh environment of turbomachines. The probe is comprised of a piezoresistive sensor and a pair of thin-film gauges that measure the unsteady pressure and temperature, respectively. The unsteady relative entropy can thus be determined. The design, manufacture and calibration of the probe are first presented in detail. Its application to detail the unsteady entropy field, and associated losses, in a centrifugal compressor, axial turbine and film cooling flows are then described.

The Thermodynamics of Wake Blade Interaction in Axial Flow Turbines: Combined Experimental and Computational Study

This paper reports on insights into the detailed thermodynamics of axial turbine nozzle guide vane (NGV) wakes as they interact with the rotor blades. The evidence presented is both computational and experimental. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations are used to compare the experimental observations with theoretical predictions. Output processing with both Eulerian and Lagrangian approaches is used to track the property variation of the fluid particles. The wake is found to be hot and loses heat to the surrounding fluid. The Lagrangian output processing shows that the entropy of the wake will fall due to heat loss as it passes through the rotor and this is corroborated experimentally. The experimental vehicle is a 1.5-stage shroudless turbine with modest Mach numbers of 0.5 and high response instrumentation. The entropy reduction of the wake is determined to be about four times the average entropy rise of the whole flow across the rotor. The results show that the work done by the wake fluid on the rotor is approximately 24% lower than that of the free-stream. The apparent experimental efficiency of the wake fluid is 114% but the overall efficiency of the turbine at midheight is around 95%. It is concluded that intrafluid heat transfer has a strong impact on the loss distribution even in a nominally adiabatic turbine with moderate row exit Mach numbers of 0.5.

Aerothermal Performance of Streamwise and Compound Angled Pulsating Film Cooling Jets

The quantification of aerothermal loss is carried out for streamwise and compound angled film cooling jets with and without large scale pulsation. This paper reports on the simultaneous measurements of the unsteady pressure and temperature field of streamwise and a 60 deg compound angled film cooling jet, both with a 30 deg surface angle over a flat plate with no pressure gradients. Turbine representative nondimensionals in terms of the geometry and operating conditions are studied. The main fiow is heated more than the injected flow to have a temperature difference and hence a density ratio of 1.3, while the blowing ratio is maintained at 2. The entropy change, derived from pressure and temperature measurements, is calculated by using modified reference conditions to better reflect the losses in both the jet and the freestream. The effects of the periodic unsteadiness associated with rotating machinery are simulated by pulsating the jets. These effects are documented through time-resolved entropy change contours. Mass-averaged entropy and kinetic energy loss coefficients seem to be apt quantities for comparing the aerothermal performance of streamwise and compound angled injections. It is observed that the mass-averaged entropy loss of a streamwise jet doubles when it is pulsated, whereas that of a compound angled jet increases by around 50%. It may be conjectured from the measurements shown in this study that streamwise oriented jets suffer most of their entropy losses at the hole exit due to separation, whereas in compound angled jets, downstream thermal mixing between the jet and the freestream is the dominant mechanism.

Unsteady Wet Steam Flow Measurements in a Low-Pressure Test Steam Turbine

Turbo Machinery Research Department, Research & Development Center, Mitsubishi Hitachi Power System, Ltd. 1-1, Saiwai-cho, 3-chome, Hitachi-city, Ibaraki, 317-0073 Japan, chongfei_duan@mhps.com, koji_ishibashi@mhps.com, shigeki1_senoo@mhps.com Laboratory for Energy Conversion, Department of Mechanical and Process Engineering, ETH Zurich IET, ML J 33, Sonneggstr, 3, CH-8092, Zurich, Switzerland bosdas@lec.mavt.ethz.ch, michel.mansour@lec.mavt.ethz.ch, rabhari@lec.mavt.ethz.ch Department of Mechanical Engineering, Aristotle University of Thessaloniki 54124, Thessaloniki, Greece anestis.kalfas@lec.mavt.ethz.ch

Unsteady Wet Steam Flow Field Measurements in the Last Stage of Low Pressure Steam Turbine

Modern steam turbines need to operate efficiently and safely over a wide range of operating conditions. This paper presents a unique unprecedented set of time-resolved steam flowfield measurements from the exit of the last two stages of a low pressure (LP) steam turbine under various volumetric massflow conditions.The measurements were performed in the steam turbine test facility in Hitachi city in Japan. A newly developed fast response probe equipped with a heated tip to operate in wet steam flows was used. The probe tip is heated through an active control system using a miniature high-power cartridge heater developed in-house.Three different operating points, including two reduced massflow conditions, are compared and a detailed analysis of the unsteady flow structures under various blade loads and wetness mass fractions is presented. The measurements show that at the exit of the second to last stage the flow field is highly three dimensional. The measurements also show that the secondary flow structures at the tip region (shroud leakage and tip passage vortices) are the predominant sources of unsteadiness at 85% span. The high massflow operating condition exhibits the highest level of periodical total pressure fluctuation compared to the reduced massflow conditions at the inlet of the last stage. In contrast at the exit of the last stage, the reduced massflow operating condition exhibits the largest aerodynamic losses near the tip. This is due to the onset of the ventilation process at the exit of the LP steam turbine. This phenomenon results in 3 times larger levels of relative total pressure unsteadiness at 93% span, compared to the high massflow condition. This implies that at low volumetric flow conditions the blades will be subjected to higher dynamic load fluctuations at the tip region.Copyright

Unsteady Flow Field and Coarse Droplet Measurements in the Last Stage of a Low Pressure Steam Turbine With Supersonic Airfoils Near the Blade Tip

The largest share of electricity production worldwide belongs to steam turbines. However, the increase of renewable energy production has led steam turbines to operate under part load conditions and increase in size. As a consequence long rotor blades will generate a relative supersonic flow field at the inlet of the last rotor. This paper presents a unique experiment work that focuses at the top 30% of stator exit in the last stage of an LP steam turbine test facility with coarse droplets and high wetness mass fraction under different operating conditions. The measurements were performed with two novel fast response probes. A fast response probe for three dimensional flow field wet steam measurements and an optical backscatter probe for coarse water droplet measurements ranging from 30 up to 110μm in diameter. This study has shown that the attached bow shock at the rotor leading edge is the main source of inter blade row interactions between the stator and rotor of the last stage. In addition, the measurements showed that coarse droplets are present in the entire stator pitch with larger droplets located at the vicinity of the stator’s suction side. Unsteady droplet measurements showed that the coarse water droplets are modulated with the downstream rotor blade-passing period. This set of time-resolved data will be used for in-house CFD code development and validation.© 2016 ASME

Time-Resolved Near-Wake Measurements of a 2MW Wind Turbine

This paper presents time-resolved velocity measurements performed in the near wake of a multi-megawatt wind turbine, using a novel nacelle-mounted fast-response aerodynamic probe. The aerodynamic probe, which has been developed at ETH Zurich, consists of a hemispherical 5-hole probe equipped with fast-pressure sensors. The probe has a measurement uncertainty of ±0.1m/s and a measurement bandwidth of 65Hz. In addition to measurement of the three-dimensional wind velocity vector, the probe is instrumented for the real-time monitoring of meteorological conditions. The measured data are processed in real-time, stored on on-board and accessible via a GPRS modem. As the aerodynamic probe is installed adjacent to the wind turbine’s ultrasonic anemometer, the measurements of the two systems can be compared. The measured wind speeds are found to be in very good agreement and remains on an averaged within ±0.24m/s deviation to the ultrasonic anemometer. The measured yaw angle shows an average offset of −7.5°. This difference is observed since the ultrasonic anemometer does not accurately capture the turning of the flow across the wind turbine’s rotor. From the time-resolved measurements of the aerodynamic probe, the phase-lock averaged measurements show that over one blade passing period the turbulence intensity varies from 13 to 24%, with a maximum degree of anisotropy above 1.4. It is found that a hub passage vortex, which extends over more than 50% of the blade passage width, is present. Thus, from a turbine control perspective the actual placement of the ultrasonic anemometer, even when corrected, can lead to high yaw angle misalignment when the wind turbine is located in moderately or highly complex terrain.© 2013 ASME

Aerothermal Aspects of a Pulsated Inclined Film Cooling Jet in Crossflow

†The present work is conducted to extend the experimental database for validation of an enhanced 3D film cooling model. This paper reports the simultaneous measurements of the pressure and temperature field of streamwise film cooling jet over a flat plate with 30° flow angle. Turbine representative operating conditions and geometry are studied. The main flow is heated at a temperature above the injected coolant to simulate a density ratio of 1.29, while the blowing ratio is maintained at average value of 2. The measurements are performed using a novel fast-response entropy probe, which enables the simultaneous measurement of time-resolved total temperature and pressure. These two measurements are then combined to obtain the kinetic energy loss coefficient and the entropy change, as well as the streamwise baroclinic vorticity production term. The effect of unsteadiness on the aerothermal field, aerothermal losses and baroclinic vorticity is documented. Pulsation is seen to increase the aerothermal losses and baroclinic vorticity production compared to a steady jet.