Aft Deck Research Articles

Investigation of flow characteristics of various-aspect-ratio rectangular nozzles with an aft deck

This study presents an experimental and numerical investigation to characterize the plume pattern of a high-aspect-ratio rectangular convergent/divergent nozzle with an aft deck in under-expanded conditions. The function of an aft deck is to shield the infrared signal of an exhaust plume at its strongest intensity located at the immediate downstream region of the nozzle exit. However, this practice may cause undesirable plume deflection, which needs to be reduced as much as possible. The nozzle pressure ratios ranged from 2 to 4, and the effect of the nozzle exit aspect ratio was examined using wall static pressure measurements and schlieren visualization for cold flows. The experimental setup involved a 3D-printed aft deck nozzle made of acrylonitrile butadiene styrene material, which underwent surface smoothing using acetone vapor. Numerical simulations were conducted using the commercial STARCCM+ software to analyze static pressure ratio variations at the aft deck. The investigation revealed that a nozzle pressure ratio of 3 induced a downward plume deflection at aspect ratio values of 6.77 and 7.54, while an increased aspect ratio of 8.35 resulted in the horizontal ejection of the plume. Moreover, at an aspect ratio of 8.35, the plume was ejected horizontally for nozzle pressure ratios ranging from 2 to 4. At a nozzle pressure ratio of 4, the flow separated from the deck without reattaching, and the plume moved horizontally with minimal deflection. The findings suggest that a combination of a high aspect ratio and sufficiently high nozzle pressure ratio can effectively reduce plume deflection.

Numerical investigation into the effects of aft deck angle on the flow characteristics of a serpentine nozzle

For modern military aero-engine, the serpentine nozzle with aft deck is deployed to meet the requirements of stealth and integrated design. Different from existing studies which emphasize the rectangular nozzles and corresponding infrared radiation impact, the effect of the aft deck angle on flow characteristics of serpentine nozzles with a focus on the internal flow, the shock system, the jet’s evolution, and the performance parameters are systematically investigated in this paper. This study is carried out through three-dimensional numerical simulations, which are validated by the experiment. The results show that the aft deck with different angles has a significant impact on the overall flow characteristics, such as the static pressure and the three-dimensional shock system, as a result of the asymmetry and the contraction/expansion effects on the jet. Specifically, upward-deflected aft decks lead to a re-compression effect and the variation of the internal static pressure value can be up to 7%, whereas for downward-deflected aft decks, the effect on the internal flow can be neglected in under-expansion conditions. In addition, the aft deck angle and the extent of boundary layer separation greatly affect the thrust performance and the vortex evolution, which determines the downstream evolution of the jet cross-section. Effective thrust coefficient is closely tied to the thrust vector angle, with the coefficient reaching its zenith when the thrust vector angle is closest to 0°. This study reinforces understanding of the interrelated problems and may facilitate the development of the optimal aft deck angle for various applications.

Schlieren-Based Analysis of Supersonic Multistream Control Using Data-Driven and Filtering Techniques

Synchronized time-resolved schlieren and far-field pressure measurements were used to examine control of a supersonic multi-aperture rectangular single- expansion ramp nozzle with an aft deck. The design contains core (Mach 1.6) and bypass (sonic) streams mixing behind a splitter plate, generating a high-frequency tone. Control was applied through splitter-plate trailing-edge spanwise waviness (passive), spanwise-arranged microjet blowing actuators (active), and their combination (hybrid). Passive and hybrid control successfully alleviate the tone, whereas active control amplifies and alters the tone frequency. Time-averaged schlieren data show changes to mean shock structures with control. Spectral proper orthogonal decomposition (SPOD) spectra from the raw schlieren data are consistent with the far-field measurements and reveal coherent structural details. Radiation associated with high-frequency structures is inhibited by passive and hybrid control that enhance mixing, but not by active control. Momentum potential theory filtering prior to SPOD application augments the analysis by isolating irrotational content, providing additional clues on acoustic vs hydrodynamic mechanisms. The results indicate shock–shear-layer interaction and shedding as sources of low- and high-frequency content, respectively. As such, through suitable processing, relatively easy-to-obtain high-speed schlieren provides a powerful tool to assess complex flow-control physics.

Study on the Effects of Aft Deck Geometry on Plume Shield Ratio

Study on the Effects of Aft Deck Geometry on Plume Shield Ratio

Flow and surface loading induced by a supersonic jet over an aft deck

Aircraft designs may include an engine that exhausts over the upper fuselage of the aircraft. This design has many benefits including reduced noise below the aircraft. However, the scrubbing of the high-speed turbulent jet flow over the fuselage has the potential to cause structural fatigue. This paper describes a joint experimental/computational study of the surface pressure fluctuations induced by the supersonic jet flow. The model configuration consists of a rectangular convergent-divergent nozzle that exhausts over a flat plate. The plate is a continuation of the lower lip of the nozzle. Pressure measurements are made at several locations on the plate surface. In addition, schlieren visualization is used to identify the jet's shock cell structure. Numerical simulations are performed using Large Eddy Simulation (LES). Results are compared between the simulations and the experiments. The importance of shock turbulent boundary layer interaction to the surface loading is identified.

Underexpanded Supersonic Jets from Elliptical Nozzle with Aft Deck

An experimental investigation of an underexpanded supersonic jet issuing from a circular nozzle, an elliptical nozzle, and an elliptical nozzle with an aft deck at different nozzle pressure ratios (NPRs) is reported in this paper. Static-pressure measurements over the nozzle walls were analyzed to understand the internal flow structure. Schlieren visualization and conical probe measurements were conducted to elucidate the development of the jets issuing from the nozzles. The sound-pressure level in the near field was measured, and it was found that the screech amplitudes were 26 dB lower in the elliptical nozzle with an aft deck. The screech-tone frequencies were observed to be above and near audible region (16 kHz) in the presence of the aft deck at NPRs 3 and 4. The jets emanating from the circular and truncated elliptical nozzles were observed to be flapping about the jet axis at NPRs 3 and 4. The unsteadiness of the jet was reduced by locking the jet onto the aft deck. The centerline Mach-number decay revealed that, due to the screeching effect, the truncated elliptical nozzle has a shorter potential core length and larger jet spreading. The flow separation and reattachment were observed over the aft-deck surface for higher NPR conditions.

Atomic oxygen number densities in the mesosphere–lower thermosphere region measured by solid electrolyte sensors on WADIS-2

Abstract. Absolute profiles of atomic oxygen number densities with high vertical resolution have been determined in the mesosphere–lower thermosphere (MLT) region from in situ measurements by several rocket-borne solid electrolyte sensors. The amperometric sensors were operated in both controlled and uncontrolled modes and with various orientations on the foredeck and aft deck of the payload. Calibration was based on mass spectrometry in a molecular beam containing atomic oxygen produced in a microwave discharge. The sensor signal is proportional to the number flux onto the electrodes, and the mass flow rate in the molecular beam was additionally measured to derive this quantity from the spectrometer reading. Numerical simulations provided aerodynamic correction factors to derive the atmospheric number density of atomic oxygen from the sensor data. The flight results indicate a preferable orientation of the electrode surface perpendicular to the rocket axis. While unstable during the upleg, the density profiles measured by these sensors show an excellent agreement with the atmospheric models and photometer results during the downleg of the trajectory. The high spatial resolution of the measurements allows for the identification of small-scale variations in the atomic oxygen concentration.

Improving container ship panel stress prediction, based on another highly correlated panel stress measurement

Operational safety requires that container ships are designed to endure extreme wave loads. This paper studies extreme panel stresses simultaneously measured at two different deck locations of a container vessel sailing in the North Atlantic between Canada and Europe. Ship panel stresses contain whipping part (transient vibratory response of the hull girder due to wave impacts occurring mainly in the bow area), the latter whipping phenomenon is inherently present in on-board stress measurements. It must be noted that measured hydroelastic vessel panel stresses include other complex non-linear effects as well, for example springing.In many practical situations it would be useful to improve accuracy of some statistical predictions extracted from a certain stochastic random process, given another synchronous highly correlated stochastic process that has been measured for a longer time, than the process of interest.The latter situation may happen if one on-board sensor malfunctioned, and it yielded data record much shorter than the neighboring well-functioning sensor. In this paper the latter issue of improving extreme value prediction has been addressed. In other words, this paper studies an efficient transfer of information between two synchronous highly correlated stochastic on-board stress processes. Two correlated ship panel stress processes at mid and aft deck locations were studied in order to test efficiency of the proposed technique of improving one process extreme prediction, based on the other. This paper intends to stimulate further research and fill the gap that is currently visible in the literature on the latter important topic.

Aeroacoustics of a Planar Multistream Supersonic Nozzle with Aft Deck and Sidewalls

The exhaust plume produced by a planar, multistream supersonic nozzle is studied with and without the effect of an aft deck and sidewalls. Measurements encompass static wall pressure of the internal flow, shadowgraphy images of the exhaust plume, and far-field acoustics for a range of pressure ratios. An experimentally validated Reynolds-averaged Navier–Stokes model of the internal flow is then used to reveal how the aft deck and sidewalls allow the expanding gas to persist longer, thereby extending the location of the separation shock. Where the far-field sound is concerned, the aft deck and sidewall attachments cause a noticeable reduction in overall sound pressure levels by as much as 5 dB at shallow angles and sideline observer positions. Many of the tones associated with screech and broadband shock associated noise are also absent with the addition of the aft deck and sidewalls.

Investigation of a Supersonic Jet from a Three-Stream Engine Nozzle

A rectangular single-expansion ramp nozzle (SERN) with an aft deck is used to model the exhaust from a three-stream engine. At the nozzle exit two unmixed streams exist. The first is assumed to be a perfectly mixed flow of core and fan streams operating at a nozzle pressure ratio of 4.25 and the second is the tertiary stream operating at a nozzle pressure ratio of 1.89. Above the aft deck, the two unmixed streams merge into the jet plume. Complementary simulation and experimental data were acquired for this geometry. Simulation data were obtained using the Naval Research Laboratory’s (NRL’s) jet engine noise reduction (JENRE) code. Experimental data were gathered in the Syracuse University anechoic chamber. The experimental and computational approaches provided similar results, giving confidence in both the simulation and the newly modified test facility. Using the newly acquired data the flow and acoustics were investigated and a trade study was performed, which found a potential “low noise” condition.

Reprint of: DMD and POD of time-resolved schlieren on a multi-stream single expansion ramp nozzle

Time-resolved schlieren measurements were conducted on a supersonic rectangular multi-stream nozzle used for three-stream engines. The jet utilizes a single expansion ramp nozzle (SERN) configuration along with an bypass stream, operating at an ideally expanded bulk flow of Mj,1=1.6 and bypass stream of Mj,3=1.0. Experiments were conducted with and without an aft deck to model airframe integration. Schlieren imaging was acquired up to 100 kHz in two different orientations. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) were applied to the schlieren data to identify flow structures. Comparisons were made between the two decomposition methods in the form of spatial correlations.

DMD and POD of time-resolved schlieren on a multi-stream single expansion ramp nozzle

Time-resolved schlieren measurements were conducted on a supersonic rectangular multi-stream nozzle used for three-stream engines. The jet utilizes a single expansion ramp nozzle (SERN) configuration along with an bypass stream, operating at an ideally expanded bulk flow of Mj,1=1.6 and bypass stream of Mj,3=1.0. Experiments were conducted with and without an aft deck to model airframe integration. Schlieren imaging was acquired up to 100 kHz in two different orientations. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) were applied to the schlieren data to identify flow structures. Comparisons were made between the two decomposition methods in the form of spatial correlations.

Analysis of Cruising Fuel Conservation Capabilities of Multi-Mode Engine with the Third Contour

Based on the analysis results from the patent search and review of domestic and foreign publications in variable cycle engines (VCE) was created a classification of the possible schematic diagrams of VCE realizing three-stream engine technologies (the adaptive low pressure compressor (LPC) with air extraction behind stages, FLADE compressor, various feeding types of extraction air to the flowing path of the engine, etc.). To estimate a three-stream engine application as a part of the power-plant (PP) efficiency, was chosen an adaptive LPC technology scheme with the third contour air bypass beyond the critical section of a basic jet nozzle for which a mathematical model (MM) of the PP has been created on the basis of one-dimensional MM of the engine. The MM of the PP included 3D modeling results of the air inlet, the LPC with various air extractions to the third contour, and the jet nozzle taking into account the interaction between the basic stream and the third contour stream. The predicted performance of an air inlet have been used to estimate the changes in a total pressure restoration coefficient and an additional resistance coefficient along «a fluid contour» when air extraction is included in the third contour in several cruiser modes of flight. An integrated characteristic of the LPC has been received at various points and levels of air extraction to the third contour, and parameters of extracted air (depending on the point and amount of air extraction, and also on the fan operating mode) have been calculated. When analyzing the obtained calculation results, the effect of pressure lines displacement to the right (towards the large reduced rates), growth of efficiency values, and also position displacement of its maximum value to the left (towards the descent reduced rates) has been found. To estimate how air extraction of the third contour between the plates of an adjustable supersonic nozzle impacts on its aft deck resistance various parameters of the flowing out air in subsonic cruiser mode of flight have been calculated. As a result of calculations according to the PP MM, under near-the-earth conditions of the subsonic cruiser flight, the effective specific fuel consumption has been reduced by 12,5 %. The results reached allow us to expect significant subsonic effective fuel conservation of the three-stream engine. To prove the calculated results it is further necessary to achieve them under full-scale conditions using the engine-demonstrator.

Flow Characterization for a Shallow Single Serpentine Nozzle with Aft Deck

An experimental investigation is carried out to characterize the flow through a shallow single serpentine curved convergent nozzle with an aft deck under fully expanded and underexpanded conditions with nozzle pressure ratios ranging from 1.1 to 2.2 for cold flows by wall static pressure measurements and flow visualization of the exit jet. The study revealed initial deceleration of the flow due to the turning of the streamlines caused by the nozzle curvature. Asymmetric coefficient of pressure variation in the cross-stream direction across various nozzle pressure ratios was observed, which is caused by secondary flow created by wall curvature and transition. The acceleration of the core flow due to geometric transition, as well as the additional nozzle length, causes early transition to sonic and supersonic flows, resulting in the formation of shock cells at relatively lower Mach number in the absence of the aft deck, as can be seen from the schlieren images. However, the presence of the constant area extension section reduced the flow asymmetry. Furthermore, the presence of the aft deck prevented the formation of barrel shocks and is expected to prevent the formation Mach disk(s) at higher nozzle pressure ratios. Thus, the curvature, transition, and aft deck complemented each other.

Application of POD on time-resolved schlieren in supersonic multi-stream rectangular jets

In this paper, we present an experimental investigation of a supersonic rectangular nozzle with aft deck used for three-stream engines. The jet utilizes a single expansion ramp nozzle (SERN) configuration along with multiple streams, operating at a bulk flow Mj,1 = 1.6 and bypass stream Mj,3 = 1.0. This idealized representation consists of two canonical flows: a supersonic convergent-divergent (CD) jet and a sonic wall jet. Time-resolved schlieren experiments were performed up to 100 kHz. Proper orthogonal decomposition (POD), as suggested by Lumley for structure identification in turbulent flows, is applied to the schlieren images and the spatial eigenfunctions and time-dependent coefficients are related to the flow structures. This research seeks to lay a foundation for fundamental testing of multi-stream SERNs and the identification of the flow physics that dominate these modern military nozzles.

More unsaturated, cooking-type hydrocarbon-like organic aerosol particle emissions from renewable diesel compared to ultra low sulfur diesel in at-sea operations of a research vessel

ABSTRACTThe aerosol particle emissions from R/V Robert Gordon Sproul were measured during two 5-day research cruises (29 September–3 October 2014; 4–7 and 26–28 September 2015) at four engine speeds (1600 rpm, 1300 rpm, 1000 rpm, and 700 rpm) to characterize the emissions under different engine conditions for ultra low sulfur diesel (ULSD) and hydrogenation derived renewable diesel (HDRD) fuels. Organic aerosol composition and mass distribution were measured on the aft deck of the vessel directly behind the exhaust stack to intercept the ship plume. The ship emissions for both fuels were composed of alkane-like compounds (H/C = 1.94 ± 0.003, O/C = 0.04 ± 0.001, CnH2n) with mass spectral fragmentation patterns consistent with hydrocarbon-like organic aerosol (HOA). Single-particle mass spectra from emissions for both fuels showed two distinct HOA compositions, with one HOA type containing more saturated alkane fragments (CnH2n+1) and the other HOA type containing more monounsaturated fragments (CnH2n−1). T...

Extreme large cargo ship panel stresses by bivariate ACER method

Safety of crew, ship and cargo requires that ships are designed to endure wave load extreme events. Design values are often based on univariate statistical analysis, while actually multivariate statistics is more appropriate for modeling the whole structure.This paper studies extreme stresses simultaneously measured at two different deck locations of a container vessel operating in the North Atlantic between Europe and North America. The focus is placed on the hydroelastic structural response, particularly whipping, which refers to transient vibratory response of the hull girder due to wave impacts occurring mainly in the bow area.It must be noted however that since analysed in this paper vessel hydroelastic response is a on-board measured one, it includes all non-linear effects like both whipping and springing.Due to less than full correlation between stresses in the different ship panels, application of the multivariate, or bivariate in the simplest case, extreme value theory is of interest.Due to non-stationarity and complicated nonlinearities of the wave induced loads, as well as the human factor in the operation of ships, reliable numerical prediction of extreme hydroelastic vessel responses, including whipping, is challenging. Laboratory tests and numerical simulation tools may not fully reproduce all critical conditions that take place during real vessel operation. Therefore, measurements on-board of real ships provide a key insight into the structural responses when the vessel is at sea.This paper focuses on application of the ACER (average conditional exceedance rate) method for prediction of extreme value statistics extended to the case of bivariate time series. Application of bivariate version of ACER method is demonstrated for simultaneously measured stresses at mid and aft deck locations.

Investigation of Twin Jet Aeroacoustic Properties near a Hybrid Wing–Body Shield

In preparation for wind-tunnel acoustic experiments of a hybrid wing–body vehicle with two jet engine simulator units, a series of twin jet aeroacoustic investigations was conducted leading to increased understanding and risk mitigation. An existing twin jet nozzle system and a fabricated hybrid wing–body aft deck fuselage are combined for a 1.9% model scale study of jet nozzle spacing and jet cant angle effects, elevon deflection into the jet plume, and acoustic shielding by the fuselage body. Linear and phased array microphone measurements are made, and data processing includes the use of the deconvolution approach for the mapping of acoustic sources. Closely spaced twin jets with a 5 deg inward cant angle exhibit reduced noise levels compared with their parallel flow counterparts at similar and larger nozzle spacings. A 40 deg elevon deflection into the twin jet plume, which is required for hybrid wing–body ground rotation, can significantly increase upstream noise levels (more than 5 dB overall sound pressure level) with only minimal increases in the downstream direction. Lastly, deconvolution approach for the mapping of acoustic sources processing can resolve the noise source distribution of multiple shielded jet sources within the limits of the incoherent source assumption.

Arctic Sentinels

On a cloud-covered morning in April, Feiyue Wang trudges down the gangway of the Canadian research icebreaker CCGS Amundsen and joins three graduate students and a rifle-toting research technician on the ice below. They set out on snowmobiles across the snow-covered slab of ice adrift in the Beaufort Sea and stop at an untouched patch of the ice floe. They unload coolers, thermoses, a generator, and a variety of electric tools, as the hems of their jackets whip about in the wind. It's −15 degrees Celsius, and the winds are gusting to 30 knots. The technician strolls along the edge of the field site with the rifle slung over her shoulder and scans the horizon for polar bears. For most of the group, it's their first chance to be “on the ice” since they arrived. They've endured a full day of travel and another of safety drills and lab cleaning—Michel Gosselin, the chief scientist for this leg of the expedition, has made it clear that although their work is important, no science would be done until the labs are straightened up and bench top materials secured in case the ship had to suddenly dislodge from the ice floe. Samples of algae, zooplankton, water, and mud have piled up in the laboratories, which are passed on from one group to the next while the Amundsen is at sea. Despite the harsh conditions, the team works for hours without a break. They extract four-foot-long (~1.25-meter-long) ice cores from the floe and scoop up surface snow and seawater (see Figure 1). They will later analyze the samples in the onboard laboratories (see Box 1) to study the presence of mercury and other contaminants, tracing their paths from terrestrial and atmospheric sources to ocean waters and, ultimately, to marine mammals. Wang, an environmental chemist from the University of Manitoba in Winnipeg, Canada, and his collaborators believe that climate change may be behind a recent jump in mercury accumulation in beluga whales, ringed seals, and other marine mammals. Figure 1 Getting to the Core of Climate Change Box 1: Keeping It Clean One of the unique features of the Amundsen is its onboard clean lab, built solely for the study of mercury. The lab is nestled in a white shipping container that has been chained to the aft deck of the ship. Few people are allowed access to the clean room, and no one gets though the inner door without removing her heavy down coat and boots, and donning a white zip-up suit, booties, and a cap. Inside, machines cover the bench tops and are secured by a complex system of bungee cords and hooks. Should the Amundsen begin to move or be jostled by high winds, the equipment needs to stay in place. The clean room is stocked with equipment that can measure different mercury species in snow, ice, brine, and water samples in near–real time. “We used to ship the samples back to Winnipeg,” says Gary Stern, a researcher with the Department of Fisheries and Oceans and a professor at the University of Manitoba, “but that was always an issue. The possibility of contamination was high and you wouldn't know it until you got back.” The Amundsen is the research base for Canada's largest research project of the International Polar Year, the Circumpolar Flaw Lead System Study—a Can$40 million study of the impact of climate change on the Arctic ecosystem (see Figure 2). The researchers on board are especially interested in flaw leads, or polynyas, which are long watery gaps in the ice that open up when the mobile sea ice pulls away from the stationary coastal ice. Flaw leads can stretch for many kilometers and extend throughout the Arctic region, like oblong beads on a necklace. They are frequently covered with thin new ice, or nilas, in the winter, and have high levels of primary productivity during the warmer months. They are particularly sensitive to environmental change. The Amundsen is the first icebreaker to spend the winter in or close to the flaw lead. Figure 2 Canadian Coast Guard Ship Amundsen Flaw leads are expected to become more prevalent in the years ahead, as rising temperatures and melting sea ice create an increasingly ice-free Arctic. Flaw leads may be longer and wider and covered with thinner ice in the winter and early spring. “They're a proxy of what can happen in the future,” says Gosselin. By studying the flaw leads, researchers hope to understand how climate change might alter mercury cycling in the Arctic and how both may interact to affect the Arctic ecosystem.

Flight demonstration project for low‐sonic boom design technology

Japan Aerospace Exploration Agency (JAXA) has promoted a supersonic technology research program including flight demonstration since 1997. In this program, JAXA is now planning the new flight demonstration project ‘‘Silent Supersonic Technology Demonstrator Project (S3TD).’’ One of the targets of this project is to demonstrate the low sonic boom aircraft concept to reduce sonic boom intensity by 50% as compared with conventional configuration and to modify the sonic boom signature for not only front shock boom but also the rear shock one. JAXA will develop a new flight demonstrator that is an unmanned vehicle of approximately 3 tons in weight and 13 m in length, and then JAXA will make flight trials by 2012. Now JAXA is designing the base‐line configuration, using the CAD‐based Automatic Panel Analysis System that we have developed. The shock overpressure of the S3TD base‐line configuration is estimated to be about 0.23 psf for front shock and 0.21 psf for rear shock, corresponding to about 50% intensity as compared with those of N‐wave signature estimated by the first‐cut method. The robustness of the low boom signature is also considered. The rear shock boom signature is so sensitive to flight condition that some small device is installed around the aft deck.