Large-scale instabilities in a STOVL upwash fountain

The fountain flow created by two underexpanded axisymmetric, turbulent jets impinging on a ground plane was studied through the use of laser-based experimental techniques. Velocity and turbulence data were acquired in the jet and fountain flow regions using laser doppler velocimetry and particle image velocimetry. Profiles of mean and rms velocities along the jet centreline are presented for nozzle pressure ratios of two, three and four. The unsteady nature of the fountain flow was examined and the presence of large-scale coherent structures identified. A spectral analysis of the fountain flow data was performed using the Welch method. The results have relevance to ongoing studies of the fountain flow using large eddy simulation techniques

Controlling unsteady cavity flows using internal structures

We report experimental measurements and preliminary analysis on a series of geometric modifications to a rectangular cavity, aimed at alleviating the severity of the aeroacoustic environment. The cavity had a length-to-depth ratio of 5 and a width-to-depth ratio of 1, and featured a simplified representation of a generic missile on the centre line. The modifications consisted of full width and depth ribs or “collars” with a cutout for the missile. Collars could be fitted at various combinations of locations in the cavity and were either straight (i.e. perpendicular to the cavity centre line), leaned or yawed. The cavity flowfield was characterised by surface pressure measurements along the ceiling. Judging from the available measurements the presence of collars modified the mean pressure distribution, and appeared to reduce the acoustic tones and generally lower the broadband noise

Mutual interference between jets and intakes in STOVL aircraft

During wind tunnel testing of jet-lift, short take-off and vertical landing (STOVL) aircraft it is usual to simulate the jet efflux but not the intake flows. The intakes, which are commonly faired over or are unpowered, are generally tested in separate wind tunnel experiments. The forces acting on the wind tunnel model are determined by the linear addition of the forces obtained from the two separate tests. There is some doubt as to whether this is a valid approach. A systematic experimental investigation was, therefore, conducted to determine the magnitude of any jet/intake interference effects on a generic jet-lift STOVL aircraft in transitional flight, out of ground effect. Comparisons made between separate and simultaneous jet and intake testing concluded that a mutual jet/intake interference effect does exist. The existence of this interference means that the aerodynamic wing lift loss in transitional flight deduced from isolated jet and intake testing is less than the lift loss obtained from simultaneous jet and intake testing. The experimental research was supplemented by some simplified computational fluid dynamics (CFD) studies of elements of the flow-field about the aircraft using the k-e turbulence model. The numerical modelling enabled aspects of the flow-field around the aircraft to be visualised which could not easily be done using the experimental apparatus. It is a requirement of the Eng]) programme that part of this thesis must address a management topic linked to the research. In this case the management aspects of wind tunnel project work were examined. A scenario was developed which established a requirement for a large-scale, low-speed wind tunnel with a Reynolds number capability of 20 million. A study was performed on the decision-making process and investment appraisal methods used in the procurement of such a wind tunnel.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Isoaspartate, Carbamoyl phosphate synthase-1, and carbonic anhydrase-III as biomarkers of liver injury

We had previously shown that alcohol consumption can induce cellular isoaspartate protein damage via an impairment of the activity of protein isoaspartyl methyltransferase (PIMT), an enzyme that triggers repair of isoaspartate protein damage. To further investigate the mechanism of isoaspartate accumulation, hepatocytes cultured from control or 4-week ethanol-fed rats were incubated in vitro with tubercidin or adenosine. Both these agents, known to elevate intracellular S-adenosylhomocysteine levels, increased cellular isoaspartate damage over that recorded following ethanol consumption in vivo. Increased isoaspartate damage was attenuated by treatment with betaine. To characterize isoaspartate-damaged proteins that accumulate after ethanol administration, rat liver cytosolic proteins were methylated using exogenous PIMT and 3H-S- adenosylmethionine and proteins resolved by gel electrophoresis. Three major protein bands of ~75-80 kDa, ~95-100 kDa, and ~155-160 kDa were identified by autoradiography. Column chromatography used to enrich isoaspartate-damaged proteins indicated that damaged proteins from ethanol-fed rats were similar to those that accrued in the livers of PIMT knockout (KO) mice. Carbamoyl phosphate synthase-1 (CPS-1) was partially purified and identified as the ~160kDa protein target of PIMT in ethanol-fed rats and in PIMT KO mice. Analysis of the liver proteome of 4-week ethanol-fed rats and PIMT KO mice demonstrated elevated cytosolic CPS-1 and betaine homocysteine S-methyltransferase-1 when compared to their respective controls, and a significant reduction of carbonic anhydrase-III (CA-III) evident only in ethanol-fed rats. Ethanol feeding of rats for 8 weeks resulted in a larger (~2.3-fold) increase in CPS-1 levels compared to 4- week ethanol feeding indicating that CPS-1 accumulation correlated with the duration of ethanol consumption. Collectively, our results suggest that elevated isoaspartate and CPS-1, and reduced CA-III levels could serve as biomarkers of hepatocellular injury

Turbulence measurements in a Short Take-Off Vertical-Landing fountain

THE wall jets created by the impingement on the ground of the individual jet flows from a jet-lift short take-off and vertical landing (STOVL) aircraft with two nozzles meet at a stagnation line and form an upward-flowing fountain that interacts with the airframe (Fig. 1). While it is evident that the fountain upwash flow is unsteady, only limited data on the transient characteristics of this flow region are available. Early experiments relied on intrusive measurement techniques to provide mean pressure data [1] with unsteady pressures on the ground plane being used to infer additional information [2]. Direct measurement of turbulence data has been made using hot-wire anemometry [3,4], however, this technique is limited to low flow speeds and low turbulence intensities and is, therefore, likely to be inaccurate for compressible and highly unsteady flows; there is also the issue of probe interference. Techniques such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) offer the possibility of detailed nonintrusive measurements in the fountain region. Recently, we have reported on the mean impinging-jet and fountain-velocity profiles obtained using PIV and LDV [5-7]. This paper extends the work further by presenting PIV-derived fountain turbulence characteristics

Computational investigation of cavity flow control using a passive device

In this paper, the results of computational studies on the unsteady flow features in threedimensional empty cavities and cavities with a representative store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard Reynolds-averaged Navier-Stokes (RANS) model within the attached boundary layer and as a Large-Eddy Simulation LES Sub-Grid Scale model in the rest of the flow (commonly known as Detached-Eddy Simulation [DES]) are used in this study. The time-mean flow study showed the presence of three-dimensional effects inside the cavities. The mean flowfield visualisation also clearly showed the presence of a pair of 'tornado-like' vortices in the upstream half of the cavity which merge to a single, large recirculation further downstream. Visualisation for the cavity-with-store case revealed that the mean flowfield was effectively divided into two halves with signifiant reduction of the spanwise flow across the cavity width. In the unsteady flow study, near-field acoustic spectra were computed for the empty cavity and cavity-with-store cases. Study of unsteady pressure spectra for the cavitywith- store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling, between the Rossiter modes. This may be the reason for the co-existence of multiple modes without the coupling among them

Computational study of cavity flowfield at transonic speeds

In this paper, the results of a computational study on the unsteady flow features in three-dimensional empty cavities and a cavity with a store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard RANS model within the attached boundary layer and as a LES Sub-Grid Scale model in the rest of the flow, including the separated regions, are used in this study. The time-mean flow study showed the existence of spanwise flow in the 3D cavity. In the unsteady flow study, computed near- field acoustic spectra were for empty cavity as well as cavity-withstore cases. Unsteady results from an empty cavity case are compared with experimental data and the frequency of the dominant mode is in good agreement with the experiment. Study of unsteady pressure spectra for the cavity-with-store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The mean flowfield visualisation for the cavity-with-store case clearly showed that the mean flowfield was effectively divided into two halves with signifiant reduction of the spanwise flow across the cavity width. This blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling between, the Rossiter modes. This may be the reason for the coexistence of multiple modes without the coupling among them

On the Characteristics of a Twin-Jet STOVL Fountain

Presented at International powered lift conference London 22-24 July 2008The interaction of multiple jets with the ground is of great importance for the design and operation of short take-off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry and laser Doppler velocimetry. Measurements were made with nozzle pressure ratios of between 1.05 and 4, nozzle height-to-diameter ratios of between 2.4 and 8.4, nozzle splay angles of between 15 degrees and a nozzle spacing-to-diameter ratio of seven. The effect of varying these parameters on the fountain velocity decay, spreading rate and momentum flux ratio are discussed. Mean fountain upwash velocity profiles were found to be self-similar for all test conditions. A distinct frequency of fountain oscillation was identified but only at a nozzle height of 4.4 diameters

On the near wake of a Formula One front wheel

Velocity measurements were made in the near wake of the front wheel of a Formula One car using a laser Doppler anemometer. Tests were carried out on a 50% scale in a closed-return three-quarter open-jet wind tunnel. Three configurations were investigated to determine the effect of both the car and an external wheel support strut on the wheel wake. In each of the configurations the test Reynolds number, based on the wheel diameter, was 6.8 × 105. Three components of the velocity were measured at two planes less than than 1.0D(whereDis the wheel diameter) downstream of the wheel axis. These data were used to visualise the extent of the wake, the flow structures present and also the streamwise turbulence intensity. The presence of the car was found to alter significantly the structure of the wheel wake when compared with an isolated wheel. In addition, the external support strut was found to have less impact in the presence of the car than previous isolated wheel studies have suggested. No previous such studies appear to have been published in the open literature