Passive flow control study in a convoluted intake using Stereo Particle Image Velocimetry

The ability of vortex generators (VG) to reduce the unsteady distortion at the exit plane of an S-duct (AIP) is investigated. The 3 components of the velocity at the AIP were measured using a Stereo Particle Velocimetry system with high spatial resolution. This enabled an assessment of the synchronous swirl distortion at the duct exit. A total of nine VG cases have been investigated with a systematic variation of key design variables. Overall the VGs change the duct secondary flows and separation and are able to substantially restructure the flow field at the AIP. The pressure distortion could be reduced up to 50% and a reduction in pressure loss of 30% was achieved for the mean flow field. The VGs have a substantial influence on the unsteadiness of the flow field with a reduction in peak swirl unsteadiness of 61% and an overall reduction of unsteady swirl distortion of 67%. They also suppress the primary unsteady flow switching mechanism of the datum configuration which is associated with the oscillation of bulk and twin swirl regimes. Consequently, extreme events which leads to high swirl intensity are suppressed which lower by 45% the maximum swirl intensity for the VG cases

Dynamic flow distortion investigation in an S-duct using DDES and SPIV data

The dynamic flow distortion generated within convoluted aero-engine intakes can affect the performance and operability of the engine. There is a need for a better understanding of the main flow mechanisms which promote flow distortion at the exit of S-shaped intakes. This paper presents a detailed analysis of the main coherent structures in an S-duct flow field based on a Delayed Detached Eddy Simulation (DDES). The DDES capability to capture the characteristics of the highly unsteady flow field is demonstrated against high resolution, synchronous Stereoscopic Particle Image Velocimetry (SPIV) measurements at the Aerodynamic Interface Plane (AIP). The flow field mechanisms responsible for the main AIP perturbations are identified. Clockwise and counter-clockwise stream-wise vortices are alternately generated around the separation region at a frequency of St=0.53, which promotes the swirl switching at the AIP. Spanwise vortices are also shed from the separation region at a frequency of St=1.06, and convect downstream along the separated centreline shear layer. This results in a vertical modulation of the main loss region and a fluctuation of the velocity gradient between the high and low velocity flow at the AIP

Passive flow control study in an S-duct intake using Stereo Particle Image Velocimetry

The ability of vortex generators to reduce the unsteady distortion at the exit plane of an S duct is investigated. The three components of the velocity at the aerodynamic interface plane were measured using a stereo particle velocimetry system with high spatial resolution. This enabled an assessment of the synchronous swirl distortion at the duct exit. A total of nine vortex generator cases have been investigated with a systematic variation of key design variables. Overall, the vortex generators change the duct secondary flows and separation and are able to substantially restructure the flowfield at the aerodynamic interface plane. The pressure distortion could be reduced up to 50%, and a reduction in pressure loss of 30% was achieved for the mean flowfield. The vortex generators had a substantial influence on the unsteadiness of the flowfield with a reduction in peak swirl unsteadiness of 61% and an overall reduction of unsteady swirl distortion of 67%. They also suppressed the primary unsteady flow switching mechanism of the datum configuration, which is associated with the oscillation of bulk and twin swirl regimes. Consequently, extreme events that lead to high swirl intensity are suppressed, which lower by 45% the maximum swirl intensity for the vortex generator cases

Convoluted intake distortion measurements using stereo particle image velocimetry

The unsteady distorted flowfields generated within convoluted aeroengine intakes can compromise the engine performance and operability. Therefore, there is a need for a better understanding of the complex characteristics of the distorted flow at the exit of S-shaped intakes. This work presents a detailed analysis of the unsteady swirl distortion based on synchronous, high-spatial-resolution measurements using stereoscopic particle image velocimetry. Two S-duct configurations with different centerline offsets are investigated. The high-offset duct shows greater levels of dynamic and steady swirl distortion and a notably greater tendency toward bulk swirl patterns associated with high swirl distortion. More discrete distortion patterns with locally high swirl levels and the potential to impact the engine operability are identified. The most energetic coherent structures of the flowfield are observed using proper orthogonal decomposition. A switching mode is identified that promotes the alternating swirl switching mechanism and is mostly associated with the occurrence of potent bulk swirl events. A vertical mode that characterizes a perturbation of the vertical velocity field promotes most of the twin swirl flow distortion topologies. It is postulated that it is associated with the unsteadiness of the centerline shear layer

Delayed detached-eddy simulation and particle image velocimetry investigation of S-Duct flow distortion

The dynamic flow distortion generated within convoluted aeroengine intakes can affect the performance and operability of the engine. There is a need for a better understanding of the main flow mechanisms that promote flow distortion at the exit of S-shaped intakes. This paper presents a detailed analysis of the main coherent structures in an S-duct flowfield based on a delayed detached-eddy simulation. The capability of this numerical approach to capture the characteristics of the highly unsteady flowfield is demonstrated against high-resolution, synchronous stereoscopic particle image velocimetry measurements at the aerodynamic interface plane. The flowfield mechanisms responsible for the main perturbations at the duct outlet are identified. Clockwise and counterclockwise streamwise vortices are alternately generated around the separation region at a frequency of St=0.53 St=0.53 , which promote the swirl switching at the duct outlet. Spanwise vortices are also shed from the separation region at a frequency of St=1.06 St=1.06 and convect downstream along the separated centerline shear layer. This results in a vertical modulation of the main loss region and a fluctuation of the velocity gradient between the high- and low-velocity flow at the aerodynamic interface plane

Experimental aerodynamic investigation of a Krueger flap device using Particle Image Velocimetry

This paper presents the initial assessment of one of the validation experiments of the Unsteady High-lift Aerodynamics - Unsteady RANS validation project (UHURA). The aim of the study is to investigate the unknown aerodynamic characteristics of a slotted Krueger flap during deployment and retraction phases. The DLR-F15 airfoil model was equipped with a full span actuated Krueger device. A test campaign was conducted at the ONERA L1 wind tunnel. The test included measurements of steady and unsteady pressures along with phase locked Particle Image Velocimetry to achieve high quality validation data for the UHURA project. The results highlighted the transient behaviour of the flow during the deployment of the Krueger

Characteristics of unsteady total pressure distortion for a complex aero-engine intake duct

Some types of aero-engine intake systems are susceptible to the generation of secondary flows with high levels of total pressure fluctuations. The resulting peak distortion events may exceed the tolerance level of a given engine, leading to handling problems or to compressor surge. Previous work used distortion descriptors for the assessment of intake-engine compatibility to characterise modestly curved intakes where most of the self-generated time-dependent distortion was typically found to be dominated by stochastic events. This work investigates the time-dependent total pressure distortion at the exit of two high off-set diffusing S-duct intakes with the aim of establishing whether this classical approach, or similar, could be applied in these instances. The assessment of joint probability maps for time dependent radial and circumferential distortion metrics demonstrated that local ring-based distortion descriptors are more appropriate to characterise peak events. Extreme Value Theory (EVT) was applied to predict the peak distortion levels that could occur for a test time beyond the experimental data set available. Systematic assessments of model sensitivities to the de-clustering frequency, the number of exceedances and sample time length were used to extend the EVT application to local distortion descriptors and to provide guidelines on its usage

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Experimental and computational aerodynamic studies of convoluted intake ducts.

Complex aero-engine intakes for embedded propulsion systems are expected to play a major role in the next generation of aircraft. However, convoluted intake diffusers can lead to the development of distorted flows with high levels of unsteady total pressure and swirl distortion. This may exceed the tolerance level of a given engine and lead to compressor surge and performance degradation. Historically, flow control devices were used to reduce the distortion to acceptable levels for the engine. However, the effect of flow control devices on the important unsteady flow field distortion has received little attention. Conventionally, flow distortion assessment for an intake relies on a limited number of time dependent total pressure measurements and even fewer steady swirl measurements at the Aerodynamic Interface Plane (AIP). However, these conventional measurement techniques have a relatively low spatial resolution and the lack of unsteady swirl data are insufficient to capture the characteristics of the unsteady distortion for convoluted intakes. This work presents the assessment of the unsteady distortion for two representative S-ducts as well as the impact of vortex generator flow control devices. The flow field at the AIP was mainly assessed with Stereo-Particle Image Velocimetry which provided synchronous high spatial resolution measurements of the 3 velocity components at the AIP. The effect of the passive flow control devices was investigated through multiple configurations with a systematic change of the design variables. The unsteady flow field was also numerically investigated with the Zonal Detached Eddy Simulation (ZDES) including passive flow control devices implemented with a Chimera grid. The use of vortex generators (VGs) within the S-duct changed the secondary flow, substantially restructured and stabilised the flow field at the AIP. As a result, the total pressure recovery could be improved with a reduction in pressure loss up to 30%. The steady total pressure distortion was also reduced with an improvement of up to 50% compared with the baseline configuration. The substantial influence of the VGs on the flow field unsteadiness typically reduced the unsteady swirl distortion by 67%. Consequently, extreme events that led to high swirl intensity for the baseline configuration were suppressed and the maximum swirl intensity was reduced by 45%. Similar findings were demonstrated for both S-duct geometries with a minor effect of the inlet Mach number on the swirl distortion. The results also highlighted the main coherent flow mechanisms that drives the unsteady distortion at the AIP with the occurrence of large deviations from the time averaged flow field for the baseline configuration. An extreme value theory methodology was established to estimate the maximum levels of peak total pressure distortion for these types of S-duct intakes based on reduced experimental data sets and to provide guidelines on its usage. The ZDES model was proven to be able to simulate the unsteady flow field at the AIP, to provide the time averaged and fluctuating levels of swirl distortion within 1% and 13% respectively of the measurements. The CFD solution was able to capture the main coherent structures and their characteristic frequencies as well as the rare and intense distortion events. The strong impact of the flow control devices on the AIP flow field was also captured by the ZDES. Compared with the measurements, the ZDES calculated similar levels of reduction of mean and unsteady swirl distortion as well as the correct pressure loss levels when flow control devices were used. Overall, this work quantified the highly beneficial impact of passive flow control devices on the unsteady total pressure and swirl flow fields for S-duct intakes. The use of S-PIV provided about 200 times more measurement points at the AIP than the conventional 40 high-bandwidth Pitot probes and demonstrated the necessity to assess the unsteady swirl distortion characteristics for the assessment of aero-engine intakes. Finally, the ZDES model was shown to be able to calculate the unsteady distortion with and without flow control devices which provides a viable method for industrial applications of aero-engine intake design at a reduced computational cost.PhD in Aerospac

Numerical investigation of the unsteady distortion for an S-duct intake with mechanical vortex generators

Flow control devices are used within complex intakes to reduce the flow distortion which can adversely impact the stability and performance of embedded engines. There is a need to assess the capability of modern computational methods such as detached eddy based models to compute the unsteady flowfield and to evaluate the potential benefits of flow control devices on the unsteady distortion. This paper investigates the unsteady flowfield for an S-duct using Zonal Detached Eddy Simulations (ZDES) with passive flow control devices modelled with an overlapping Chimera grid method. The ability of ZDES to evaluate the impact of passive flow control devices on the unsteady flow distortion was assessed. The computed unsteady flowfield at the Aerodynamic Interface Plane was compared with experimental data based on total pressure and velocity field measurements. For the baseline configuration, the ZDES model has proven to be able to simulate the unsteady flowfield at the AIP, to provide the time averaged and fluctuating levels of swirl distortion within 1% and 13% respectively of the measurements. The strong impact of the flow control devices on the AIP flowfield was also captured by the ZDES. The overall increase of pressure ratio (PR) at the AIP due to the flow control devices was predicted with less than 1% error. The 65% reduction in swirl distortion fluctuation when the flow control devices are used was predicted within less than 8% error by the ZDES compared with S-PIV measurements. Overall it was determined that the ZDES method is able to simulate the unsteady flow and distortion characteristics for both the baseline reference configuration as well as the case with flow control