Unsteady Total Temperature Research Articles

Development and Application of a Fast-Response Total Temperature Probe for Turbomachinery

The measurement of unsteady total temperature is of great interest for the examination of loss mechanisms in turbomachinery with respect to the improvement of the efficiency. Since conventional thermocouples are limited in frequency response, several fast-response total temperature probes have been developed over the past years. To improve the spatial resolution compared to these existing probes and maintaining a high temporal resolution, a new fast-response total temperature probe has been developed at the Institute of Aircraft Propulsion Systems (ILA), Stuttgart, Germany in cooperation with Berns Engineers, Gilching, Germany. The design of the probe allows a sensitive measuring surface below 1 mm2. A detailed insight into the design of the probe, the measurement principle, the calibration process, and an estimation of the measurement uncertainty is given in the present paper. Furthermore, to prove the functionality of the probe, first experimental results of a simple test bed and of area traverses downstream of the first rotor of a two-stage low pressure turbine are presented. It is shown, that the new probe is capable of detecting rotor characteristic effects as well as rotor-stator-interactions. In addition, a hot-spot is investigated downstream of the first rotor of the turbine, and the findings are compared to the effects known from the literature.

Unsteady Total Temperature Measurements Downstream of a High-Pressure Turbine

An experimental technique for the measurement of flow total temperature in a turbine facility is demonstrated. Two thin film heat transfer gases located at the stagnation point of fused quartz substrates are operated at different temperatures in order to determine the flow total temperature. With this technique, no assumptions regarding the magnitude of the convective heat transfer coefficient are made. Thus, the probe can operate successfully in unsteady compressible flows of arbitrary composition and high free-stream turbulence levels without a heat transfer law calibration. The operation of the total temperature probe is first demonstrated using a small wind tunnel facility. Based on results from the small wind tunnel tests, it appears that the probe total temperature measurements are accurate to within ±1 K. Experiments using the probe downstream of a high-pressure turbine stage are than described. Both high and low-frequency components of the flow total temperature can be accurately resolved with the present technique. The probe measures a time-averaged flow total temperature that is in good agreement with thermocouple measurements made downstream of the rotor. Frequencies as high as 182 kHz have been detected in the spectral analysis of the heat flux signals from the total probe. Through comparison with fast-response aerodynamic probe measurements, it is demonstrated that the current measurement location, the total temperature fluctuations arise mainly due to the isentropic extraction of work by the turbine. The present total temperature probe is demonstrated to be an accurate, robust, fast-response device that is suitable for operation in a turbomachinery environment.

High speed rotor wake total temperature measurements using a hot-film anemometer

To develop a quantitative understanding of unsteady and interacting turbomachine flow fields, it is necessary to quantify the instantaneous efficiency of high speed turbomachines. This requires the measurement of both the unsteady velocity and total temperature variation in the exit flow of a high speed rotor. In this paper, techniques to utilize a single slant-film anemometer to measure unsteady total temperature are developed and evaluated. Then a series of preliminary experiments are performed in a high speed axial fan facility to quantify the instantaneous rotor efficiency. This is accomplished by utilizing these single slant-film methods to measure the total temperature in the rotor wakes. Results show that measurements at multiple overheats and several probe orientations are required. The simplest method proves to be useful for determining parameters used in other methods. An analysis based on King’s law gives good results even when measurements are outside the calibration range. Within the calibration range, a polynomial representation of the wire response to mass flux and total temperature yields good total temperature fluctuation results. A model analysis technique is also assessed.

Aspirating Probe Measurements of the Unsteady Total Temperature Field Downstream of an Embedded Stator in a Multistage Axial Flow Compressor

The results from the area traverse measurements of the unsteady total temperature using a high-response aspirating probe downstream of the second stator of a three-stage axial flow compressor are presented. The measurements were conducted at the peak efficiency operating point. The unsteady total temperature data are resolved into deterministic and unresolved components. Hub and casing regions have high levels of unsteadiness and consequently high levels of mixing. These regions have significant levels of shaft resolved and unresolved unsteadiness. Comparisons are made between the total temperature and the total pressure data to examine the rotor 2 wake characteristics and the temporal variation of the stator exit flow. Isentropic efficiency calculations at the midpitch location show that there is about a 4 percent change in the algebraically averaged efficiency across the blades of the second rotor and if all the rotor 2 blades were behaving as a “best” blade, the improvement in efficiency would be about 1.3 percent. An attempt is made to create a composite flow field picture by correlating the unsteady velocity data with temperature and pressure data.

Turbulence measurements and noise generation in a transonic cryogenic wind tunnel

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous measurements of unsteady total temperature and pressure were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients failed to show vorticity, entropy, or sound as the dominant mode of turbulence in the tunnel.