Bayesian Mass Averaging in Rigs and Engines

This paper introduces the Bayesian mass average and details its computation. Owing to the complexity of flow in an engine and the limited instrumentation and the precision of the sensor apparatus used, it is difficult to rigorously calculate mass averages. Building upon related work, this paper views any thermodynamic quantity's spatial variation at an axial plane in an engine (or a rig) as a Gaussian random field. In cases where the mass flow rate is constant in the circumferential direction but can be expressed via a polynomial or spline radially, this paper presents an analytical calculation of the Bayesian mass average. In cases where the mass flow rate itself can be expressed as a Gaussian random field, a sampling procedure is presented to calculate the Bayesian mass average. Examples of the calculation of the Bayesian mass average for temperature are presented, including with a real engine case study where velocity profiles are inferred from stagnation pressure measurements.

Improving heat and mass transfer rates through continuous drop-wise condensation

Drop-wise condensation (DWC) has been the focus of scientific research in vapor condensation technologies since the 20th century. Improvement of condensation rate in DWC is limited by the maximum droplet a condensation surface could sustain and the frequency of droplet shedding. Furthermore, The presence of non-condensable gases (NCG) reduces the condensation rate significantly. Here, we present continuous drop-wise condensation to overcome the need of hydrophobic surfaces while yet maintaining micron-sized droplets. By shifting focus from surface treatment to the force required to sweep off a droplet, we were able to utilize stagnation pressure of jet impingement to tune the shed droplet size. The results show that droplet size being shed can be tuned effectively by tuning the jet parameters. our experimental observations showed that the effect of NCG is greatly alleviated by utilizing this technique. An improvement by multiple folds in mass transfer compactness factor compared to state-of-the-art dehumidification technology was possible.

Non-axisymmetric complete flow conditioning gauzes

This paper presents a novel methodology for the design of a gauze that produces distributions of stagnation pressure, swirl angle, pitch angle and turbulence intensity, tailored in both the radial and circumferential directions. A distortion gauze is made from a large number of small-scale circumferential and radial blades with tailored thickness and camber distributions. By controlling the blade design independently in both the radial and circumferential directions, the target inflow pattern can be achieved. 1D correlations are used to initialise the blades and they are refined using full 3D CFD simulations. The final design is additively manufactured for use in rotating rigs. In this paper, the method has been used to reproduce four target inflow patterns with large variations in stagnation pressure and flow angularity. Two examples model the inlet flow distortion seen at the aerodynamic interface plane of an aft-mounted boundary layer ingesting fan. The final two examples model the inlet distortion at inlet to an axial compressor spool caused by upstream structural struts in a swan neck duct. The gauzes are shown to replicate the structures of the target flow in an experimental test. These kind of flow structures would be extremely difficult or impossible to replicate in an experiment in any other way. Graphical abstract

Numerical Evaluation of Losses in Shrouded and Cantilevered Stators of a Multi-Stage Axial Compressor

The loss coefficient based only on the stagnation pressure has traditionally been used in the analysis of axial compressors for the comparison between shrouded and cantilevered stator configurations. In recent years, engineers have been able to perform more detailed Computational Fluid Dynamics simulations, allowing them to resolve the flow field in the leakage paths. The two stator hub designs are, however, affected by the rotating surfaces in a different way: in cantilevered stators, the relative rotation between the stator and the hub imparts energy to the hub flow, whereas in shrouded stators, the rotating inner leakage surface imparts energy to the seal cavity leakage flow. The aim of this work is to analyze the performance of a multi-stage axial compressor featuring a change of stator hub configuration, by employing both the conventional loss coefficient based on the stagnation pressure and the loss coefficient based on the entropy change. It is shown, that in the evaluation of the losses of a multi-stage axial machine, it is essential to consider the different 3D distributions of stagnation temperature resulting from the two stator hub configurations, which are transferred to the downstream rows.

Flow Characterization of Bluff Bodies: A Two-Dimensional Transformation From Square to Triangular Cylinder

In the present study, two-dimensional unsteady, incompressible flow around a square body that is being transformed into a vertex oriented towards the flow configuration of a triangular body is numerically investigated at Re =100 using ANSYS FLUENT 19.0 software. The purpose is to explore the effect of this transformation on the wake characteristics of a square body with l/d = 1 to a triangular body with l/d = 0; where l is the length of lateral and front surface, and d is the body height. The effect on the flow behavior caused by the leading-edge transformation from the prospect of wake width, recirculation length and stagnation pressure difference is discussed. It is seen that as the l/d ratio decreases, the vortex strength increases which is attributed to the higher stagnation pressure difference value resulting in more intense rolling of the shedding vortex and a smaller wake width. For lower l/d, the fluid traverses a longer distance along the lateral surfaces resulting in greater loss of momentum and hence the lower vortex formation length. The mean drag coefficient is found to be minimum for l/d = 0.75 with stagnation pressure difference and recirculation length being the more dominating factor on this variation. The flow in all the cases separates at the rear surface and the general trend of decrease in drag coefficient with decrease in wake width is not followed. However, such modification leads to better aerodynamic outcome by weakening the periodic drag and lift forces.

Sensitivity of Multi-Stage Compressor Performance Assessment to Measurement Rake Positions

For an accurate performance assessment of a multi-stage compressor, the circumferentially non-uniform flow at the compressor exit needs to be understood and sampled in a way that minimizes uncertainties. To quantify the effect of the measurement rake positions in the exit duct on compressor performance a combined computational and experimental approach is used on a modern 4-stage compressor. The computational analysis is based on unsteady calculations of a 180-degree sector of the test compressor and experimental verification is provided by comparing to area-traverse data downstream of the outlet guide vanes. It is shown that the exit measurement rakes are subject to circumferential flow variations caused primarily by the combined effect of the potential field of the struts housed within the exit duct and the wakes originating from the outlet guide vanes. A circumferential camber pattern, applied to the outlet guide vanes, designed to shield the upstream compressor blade rows against the potential field of the exit struts, is found to reduce the amplitude of the circumferential variation in stagnation pressure and shift its circumferential phase. Recognizing that a smaller numerical model, consisting only of the last rotor, the outlet guide vanes and the exit struts, is sufficient to capture the relevant flow mechanisms, the circumferential variations in stagnation pressure and temperature at the rake position are quantified as a function of the exit capacity. The stagnation pressure and temperature uncertainty within a +/-2 deg circumferential range around the nominal rake position is found to be up to 2.25 times larger than the change of the nominal values over an 87.1–106.0% variation of the exit capacity. Three options to position the rakes to reduce the uncertainty in compressor efficiency are presented — moving the rake downstream as well as leaning and verniering the rakes over the outlet guide vane pitch. Moving the rake from the leading edge to the trailing edge plane of the exit struts reduced the efficiency uncertainty by 2.6%, while leaning and verniering the rakes reduced the efficiency uncertainty by 0.2% and 0.7% respectively. The knowledge gained from the large-scale, detailed CFD predictions can used to support future measurement campaigns.