https://ntrs.nasa.gov/search.jsp?R=20140017156 2019-03-26T11:25:30+00:00Z NASA/TM—2014–218376 Conceptual Design for a Dual-Bell Rocket Nozzle System Using a NASA F-15 Airplane as the Flight Testbed Daniel S. Jones Armstrong Flight Research Center, Edwards, California Joseph H. Ruf Marshall Space Flight Center, Huntsville, Alabama Trong T. Bui, Martel Martinez and Clinton W. St. John Armstrong Flight Research Center, Edwards, California Click here: Press F1 key (Windows) or Help key (Mac) for help October 2014 This page is required and contains approved text that cannot be changed. NASA STI Program ... in Profile Since its founding, NASA has been dedicated • CONFERENCE PUBLICATION. to the advancement of aeronautics and space science. Collected papers from scientific and technical The NASA scientific and technical information (STI) conferences, symposia, seminars, or other program plays a key part in helping NASA maintain meetings sponsored or this important role. co-sponsored by NASA. 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Scientific and technical findings that are • Fax your question to the NASA STI Information preliminary or of specialized interest, Desk at 443-757-5803 e.g., quick release reports, working papers, and bibliographies that contain minimal • Phone the NASA STI Information Desk at annotation. Does not contain extensive analysis. 443-757-5802 • CONTRACTOR REPORT. Scientific and • Write to: technical findings by NASA-sponsored STI Information Desk contractors and grantees. NASA Center for AeroSpace Information 7115 Standard Drive Hanover, MD 21076-1320 NASA/TM—2014–218376 Conceptual Design for a Dual-Bell Rocket Nozzle System Using a NASA F-15 Airplane as the Flight Testbed Daniel S. Jones Armstrong Flight Research Center, Edwards, California Joseph H. Ruf Marshall Space Flight Center, Huntsville, Alabama Trong T. Bui, Martel Martinez and Clinton W. St. John Armstrong Flight Research Center, Edwards, California Insert conference information, if applicable; otherwise delete Click here: Press F1 key (Windows) or Help key (Mac) for help National Aeronautics and Space Administration Armstrong Flight Research Center Edwards, CA 93523-0273 October 2014 Acknowledgments The authors acknowledge the contributions made by a previous NASA AFRC F-15/PFTF project called the ducted Rocket Experiment (D-Rex). Conceptual designs from this effort were greatly utilized and leveraged for this dual-bell nozzle propellant feed system conceptual design. This effort was made possible by several organizations within the agency. In particular, the authors express their appreciation to the following six groups: (1) the NASA Headquarters Center Innovation Fund; (2) the NASA AFRC Center Chief Technologist Office; (3) the NASA AFRC Exploration and Space Technology Mission Directorate Office; (4) the NASA Langley Research Center Game Changing Development Program; (5) the NASA MSFC Technology Development and Transfer Office; and (6) the NASA Kennedy Space Center Launch Services Program. Each of these groups has shown support for the ACN project, and has continued to foster the advancement of this technology for the nation. Click here: Press F1 key (Windows) or Help key (Mac) for help Available from: NASA Center for Ae roSpace Information 7115 Stand ard Drive Hanover, MD 21076-1320 443-757 -5802 Click here: Press F1 key (Windows) or Help key (Mac) for help Abstract The dual-bell rocket nozzle was first proposed in 1949, offering a potential improvement in rocket nozzle performance over the conventional-bell nozzle. Despite the performance advantages that have been predicted, both analytically and through static test data, the dual-bell nozzle has still not been adequately tested in a relevant flight environment. In 2013 a proposal was constructed that offered a National Aeronautics and Space Administration (NASA) F-15 airplane as the flight testbed, with the plan to operate a dual-bell rocket nozzle during captive-carried flight. If implemented, this capability will permit nozzle operation into an external flow field similar to that of a launch vehicle, and facilitate an improved understanding of dual-bell nozzle plume sensitivity to external flow-field effects. More importantly, this flight testbed can be utilized to help quantify the performance benefit with the dual-bell nozzle, as well as to advance its technology readiness level. Toward this ultimate goal, this report provides plans for future flights to quantify the external flow field of the airplane near the nozzle experiment, as well as details on the conceptual design for the dual-bell nozzle cold-flow propellant feed system integration within the NASA F-15 Propulsion Flight Test Fixture. The current study shows that this concept of flight research is feasible, and could result in valuable flight data for the dual-bell nozzle. Nomenclature ACN altitude-compensating nozzle AFRC Armstrong Flight Research Center (Edwards, California) AoA angle of attack CB conventional-bell CCIE Channeled Centerbody Inlet Experiment CDE Cone Drag Experiment CFD computational fluid dynamics COPV composite overwrapped pressure vessel DOF degrees-of-freedom GN gaseous nitrogen 2 I specific impulse sp LEO low-Earth orbit LMI Local Mach Investigation MEOP maximum expected operating pressure MSFC Marshall Space Flight Center (Huntsville, Alabama) NASA National Aeronautics and Space Administration NNPR normalized nozzle pressure ratio NPR nozzle pressure ratio (P /P ) c amb NTF Nozzle Test Facility OML outer mold line P ambient pressure amb P nozzle chamber pressure c PFTF Propulsion Flight Test Fixture PRA pressure reducing assembly RAGE Rake Airflow Gage Experiment RFS rocket forebody simulator SSME Space Shuttle Main Engine STS Space Transportation System TRL technology readiness level 1 Introduction Development of the dual-bell rocket nozzle has been proposed, including the goal of advancing the technology readiness level (TRL) of the dual-bell nozzle through flight testing and flight research in a relevant environment (ref. 1). A more thorough investigation on the performance of the dual-bell nozzle is warranted since this nozzle has been predicted to offer a performance advantage over the conventional-bell (CB) nozzle. If the performance benefit of the dual-bell nozzle is proven in a relevant environment, utilization of this technology could lead to a capability of delivering higher mass payloads to low-Earth orbit (LEO). The dual-bell nozzle is one type of altitude-compensating nozzle (ACN), which has a fixed geometry with an inner contour consisting of two overlapped bells. During rocket ascent at low altitudes, the dual-bell nozzle operates in mode 1, only utilizing the smaller bell of the nozzle. During rocket ascent at higher altitudes, the dual-bell nozzle operates in mode 2, also utilizing the larger bell of the nozzle. The inherent dual-mode operation of the dual-bell nozzle theoretically permits near optimal expansion at two altitudes, and overall, a higher mission integrated performance over the CB nozzle since the flow within the dual-bell nozzle will never be significantly over- or under-expanded. The concept of the dual-bell nozzle was first proposed in 1949, offering a potential method of mitigating the high performance losses incurred by the CB nozzle (ref. 2). Since then, analytical studies and static tests with the dual-bell nozzle have continued worldwide, but to the authors’ knowledge, the dual-bell nozzle has still not been adequately tested in a relevant flight environment. The National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC) (Huntsville, Alabama) is one of the few organizations that has complemented their analytical effort on the dual-bell nozzle with static tests to verify their performance predictions. MSFC conducted static testing of the dual-bell nozzle at the MSFC Nozzle Test Facility (NTF), utilizing a non-reacting flow which exhausted from the nozzle into a quiescent environment. Nozzle testing was conducted over a wide range of nozzle pressure ratio (NPR) conditions, while quantifying the nozzle performance and flow behavior at each condition. Figure 1 shows a photo of the test setup at the MSFC NTF with a dual-bell nozzle. Testing with a similar CB nozzle was also conducted at the MSFC NTF. During these tests, the dual-bell nozzle proved to provide a greater performance than the CB nozzle over a range of NPR conditions. The NASA Armstrong Flight Research Center (AFRC) (Edwards, California), formerly the NASA Dryden Flight Research Center, has a unique capability with its fleet of F-15 airplanes (McDonnell Douglas, now The Boeing Company, Chicago, Illinois), one of which can be used as a flight testbed for dual-bell rocket nozzle research (ref. 1). Captive-carried flight research expertise at AFRC led to the creation of the Propulsion Flight Test Fixture (PFTF), which was specifically created to facilitate the advancement of propulsion-focused technologies through captive-carried flight research. Figure 2 shows a photo of the PFTF (in black) mated to the centerline pylon of an F-15 airplane, while conducting captive-carried flight research with a simulated rocket (in red) (ref. 3). Several of the F-15/PFTF capabilities and limitations for the dual-bell rocket nozzle flight system have been documented (ref. 1). Among these documented capabilities and limitations are: (1) an overview of the F-15/PFTF capability; (2) the proposed nozzle placement and sizing criteria; (3) the PFTF internal capacity; (4) the PFTF thrust limitations of the force balance (a system that permits dual-bell nozzle thrust forces to be measured in flight); and (5) the F-15/PFTF flight envelope. These criteria were used to develop the conceptual design presented in this report. The flight-research campaign is designed to include three phases, which will all require tests at various flight conditions. These three flight-research phases are as follows: (Phase I) initial flight research to quantify the external (local) flow-field conditions near the nozzle; (Phase II) flights while operating cold 2 flow through various nozzles; and (Phase III) flights while operating reacting flow through various nozzles. Rationale for conducting each of the three phases of the flight-research campaign has been documented, as well as the rationale for conducting dual-bell rocket nozzle research through captive-carried flight (ref. 1). The conceptual design presented within this report covers Phase I and Phase II of the flight-research campaign. The conceptual design for Phase III of the flight-research campaign will be detailed in a separate publication. Conceptual Design for the External Flow-Field Flights (Phase I) Phase I of the dual-bell nozzle flight-research campaign will be conducted to quantify the local external flow-field conditions under the F-15/PFTF near the dual-bell nozzle. A survey of the external flow field is crucial to a greater understanding of the nozzle plume transitional behavior and must be understood prior to flights which include nozzle operation. This section will provide details on three main topics related to the Phase I flight-research campaign: (1) previous flight experiments that have been conducted with the F-15/PFTF; (2) the conceptual design for the dual-bell nozzle external flow-field flights; and (3) the initial results from the external flow-field predictions. Previous Flight Experiments Utilizing the F-15/PFTF The conceptual design for the Phase I flight system is based on the utilization of existing flight-proven hardware, with the F-15/PFTF as the flight testbed. Combined with one of the AFRC F-15 research airplanes, the PFTF provides an innovative and cost effective method for conducting flight testing and flight research of advanced propulsion concepts. AFRC expertise with captive-carried flight research led to the creation of the PFTF, which has been integrated with the centerline pylon of an F-15 airplane. The PFTF also has a six-degrees-of-freedom (6-DOF) in-flight force measurement capability for a propulsion flight research experiment carried below the PFTF (ref. 4). The PFTF has been utilized for captive-carried flight research with four previous experiments: 1) The Cone Drag Experiment (CDE), in which a cylindrical duct with a conical nose cap was used as a simulated rocket. This flight research facilitated the validation of the PFTF integral 6-DOF force balance system against aerodynamic and inertial forces in flight (ref. 5). 2) The Local Mach Investigation (LMI) flights, in which an air data boom was attached to the front of a simulated rocket. This flight research led to a quantified assessment of the local Mach number and the local flow angle at a single point under the F-15/PFTF over a wide range of flight conditions (ref. 6). 3) The Rake Airflow Gage Experiment (RAGE), in which a cruciform array of nine five-hole conical probes was attached to the front of a simulated rocket by a cylindrical boom. This flight research led to a quantified assessment of the local flow conditions at the aerodynamic interface plane of an advanced inlet experiment, over a local range of Mach 1.45 through Mach 1.6 (ref. 7). 4) The Channeled Centerbody Inlet Experiment (CCIE), in which an advanced experimental inlet was mounted under the PFTF. This flight research led to a quantified assessment of the airflow through an advanced experimental inlet, which was also compared to the airflow through a standard inlet. The CCIE flight hardware included two interchangeable center bodies, which were installed in an air inlet tube. One center body was channeled, and the other center body was a conventional smooth shape. Slots cut along the length of the channeled center body simulated a simple device that, in an actual inlet, would allow optimization of the amount of air flowing into the engine (ref. 8). External Flow-Field Conceptual Design Figure 3 shows a sketch of the conceptual design of an F-15 airplane in the ACN dual-bell nozzle flight-research configuration, which has great similarities to the previous flight-research experiments, as 3 noted above. The conceptual design for the flight-research testbed is based on the philosophy of utilizing existing flight-proven hardware to the greatest extent possible. The rationale behind this philosophy is three-fold: (1) to reduce cost; (2) to minimize schedule; and (3) to mitigate risk. The ACN-specific hardware that is captive-carried by an F-15 airplane is called the ACN stack, and consists of the following three primary components: (1) the PFTF; (2) the PFTF experiment adapter; and (3) the rocket forebody simulator (RFS). Figure 3 shows the ACN stack, which is mounted to an F-15 airplane via the centerline pylon. Both the airplane and the RFS will have air data booms to measure the incoming Mach number and flow angles, with the airplane air data boom measuring freestream conditions, and the RFS air data boom measuring incoming RFS local flow conditions. The rocket nozzle will be mounted in the aft-region of the RFS, with the nozzle exit plane coplanar with the RFS close-out plate. For the Phase I flow field survey flights, the entire RFS outer mold line (OML) will be heavily instrumented, especially near the nozzle exit plane, such that the local flow field can be quantified prior to nozzle operational flights. Although previous flight experiments have measured the local flow field near the front of the RFS (via an air data boom, or a rake), the flow field near the aft region of the RFS has never been quantified. The same RFS OML pressure instrumentation plan will be used for all three phases of flight research, to facilitate comparisons. The RFS OML instrumentation will be used to determine the local flow-field pressures along the RFS, especially near the nozzle experiment. Data from this instrumentation will also lead to the validation of computational fluid dynamics (CFD) predictions and facilitate refined analytical predictions prior to flight activity with nozzle operation. The PFTF has an internal capacity that can be used for the dual-bell rocket nozzle propellant feed system, which will be described in greater detail in the next section of this report. The PFTF main structure was fabricated from a solid billet of 6061-T6 aluminum, with an overall length of 107 inches, an overall height of 19 inches, and an overall width of 10 inches. The RFS will be mounted underneath the PFTF, and will be utilized to spatially and inertially simulate a rocket utilizing a dual-bell rocket nozzle in flight. The RFS has a cylindrical diameter of 10 inches and a 60 degree half-angle conical nose with an air data boom. All ACN flights (including non-operational nozzle flights) will utilize the PFTF 6-DOF force balance system to measure forces in flight. The limitations and accuracy of the force balance have previously been documented (refs. 4 and 5). For Phase I flights, the force balance will measure aerodynamic and inertial forces on the RFS, whereas the Phase II and Phase III flights will utilize the force balance to also measure dual-bell nozzle thrust forces in flight. Figures 4(a) and 4(b) show external images of the ACN conceptual design. Figure 4(a) shows a rear-isometric view of the ACN stack, and figure 4(b) shows a zoomed-in view with the dual-bell rocket nozzle installed within the aft section of the RFS. The purpose of the RFS is partially to help simulate a rocket in flight and aid in aligning the local flow field as it approaches the nozzle exit plane. The RFS will also be utilized to house the propellant feed system plumbing from the PFTF to the rocket nozzle, as well as to house the routing of instrumentation. As noted earlier, the conceptual design of the RFS also includes an air data boom, although an air data boom is not shown in figure 4(a). From figures 4(a) and 4(b), one can note the slight nose-up attitude of the RFS. Flight research with previous experiments utilized a nose-up attitude to align the forward end of the simulated rocket with the local flow field under the F-15/PFTF in that region, due to the local flow-field downwash from the F-15 airplane. The existing design allows for the articulation of this angle prior to flight, up to an inclination angle of five degrees with respect to the PFTF. The appropriate angle will be determined and set prior to flight to align the primary axis of the RFS with the local flow field near the nozzle for the flight-test condition planned. As noted earlier, the external (local) flow field is expected to have a significant effect on dual-bell nozzle plume behavior, including the dual-bell nozzle plume mode transition. In addition to the research benefit of aligning the nozzle with the external flow field, the RFS 4 inclination angle also provides a flight-safety benefit by providing a greater separation of the nozzle plume from the F-15/PFTF flight hardware for nozzle operational flights. The primary objective of the Phase I flow-field survey flights is to obtain the local flow field pressure data underneath the F-15/PFTF in preparation for future nozzle operational flights. CFD analysis has been completed to help predict this flow field in preparation for Phase I flight activity, and Phase I flight data will lead to the validation of this analysis. Flight data and CFD analysis will lead to a more thorough understanding of dual-bell nozzle plume sensitivity to local flow-field effects. As noted earlier, the conceptual design for the flight-research testbed is based on the philosophy of utilizing existing flight-proven hardware to the greatest extent possible. Following this philosophy, a thorough inventory of existing flight hardware was taken against the Phase I conceptual design. The conclusion of this inventory led to the Phase I conceptual design shown in figure 3, figure 4(a), and figure 4(b). With the exception of the base-plate assembly (labeled in figure 3), all components have already been flight-proven. Initial External Flow-Field Predictions As can be seen in figure 3, the ACN exit plane is not exposed to the incoming freestream static pressure, but rather, it is subjected to flow perturbations caused by the F-15 airplane, the centerline pylon, the air data booms, the PFTF, the PFTF adapter, and the RFS. ACN operation greatly depends on the nozzle exit pressure, and accurate predictions of this exit pressure are required for the design of the nozzle and the propellant feed system, as well as for the final selection of the flight-test conditions required. The main objective of this initial analysis was to determine the flow-field effects caused by the F-15 airplane with the ACN stack, and ultimately the local flow-field conditions near the ACN exit plane. This initial flow-field analysis includes: 1) airplane-only inviscid/Euler CFD analysis for the airplane with blocked airplane inlets, 2) airplane plus ACN stack inviscid/Euler CFD analysis for the airplane and the ACN stack with blocked airplane inlets, with the ACN not operating, and 3) airplane plus ACN stack inviscid/Euler CFD analysis for the airplane and the ACN stack with blocked airplane inlets, with the ACN operating. In addition, analysis is currently underway to determine the airplane and the ACN stack viscous/Navier-Stokes CFD flow-field predictions with and without experimental nozzle operation. Both the flow viscosity and the nozzle plume affect the base flow of the RFS and will influence the nozzle exit pressure. Therefore, these considerations will be included in a separate analysis. Finally, all CFD predictions will be validated using the Phase I flow field survey flight data. All nozzle operation with an F-15 airplane will occur during a low angle of attack (AoA), and the local flow field is expected to remain mostly attached. Based on this assumption, the initial predictions were completed with an inviscid/Euler CFD analysis, and should yield satisfactory results for this preliminary design and sizing effort. A comparison of the airplane-only and airplane plus ACN stack predictions was initially conducted to isolate the effects of the ACN stack on the ACN exit plane, and permit the investigation of possible flow anomalies. Blocked airplane inlets potentially produce the most disturbances to the local flow field underneath the airplane, so the addition of blocked airplane inlets was included in this initial analysis effort. No airplane engine parameters were needed for this blocked airplane inlet approximation. 5 The Star-CCM+ polyhedral finite-volume unstructured CFD code was used for this analysis effort. Figure 5 illustrates an inviscid/Euler CFD grid that was created for an F-15 airplane and the complete experimental stack. Since only changes in AoA are considered, only half of the airplane is modeled. The base-plate assembly was not modeled in the current CFD analysis, but this difference in the model is not expected to change the basic conclusions for the current results. The base-plate assembly should be included in future CFD analysis should it become a permanent fixture in the flight experiment. Two different flight-test conditions were initially considered for this analysis to gain a greater understanding of the local flow field near the nozzle exit plane: 1) 46 kft altitude, Mach 0.9, and 4.2-deg airplane AoA. 2) 46 kft altitude, Mach 1.2, and 2.6-deg airplane AoA. The 46 kft altitude was selected to provide a clean, undisturbed freestream static pressure value of 2 psi used in the current nozzle and propellant feed system design and sizing effort. The transonic and supersonic flight conditions were selected to evaluate compressibility effects on the ACN exit pressure. For the two flight conditions under consideration, the corresponding airplane AoA values were found from the F-15 airplane flight simulation deck in the Aerodynamics and Propulsion Branch at NASA AFRC. Figures 6(a) and 6(b) illustrate some preliminary CFD predictions for the local flow field underneath a clean F-15 airplane. The static pressure contours on the airplane for the Mach 0.9 flight condition are shown in figure 6(a), and the static pressure contours for the Mach 1.2 flight condition are shown in figure 6(b). It can be seen that the flow disturbances in the supersonic flight condition are more pronounced than the transonic flight condition. For each condition, an average of pressures was obtained in the location of the nozzle exit plane. The averaged nozzle exit pressure for the transonic flight condition is 1.93 psi, and is only slightly less than the freestream static pressure value of 2 psi. For the supersonic flight condition, the averaged nozzle exit pressure value is 1.70 psi and is further below the freestream static pressure. Despite the disturbances created by the airplane nose and inlet, it can be seen from the streamlines that smooth flow exists underneath the airplane for both the transonic and supersonic cases. It can be seen in both cases that the blocked airplane inlet produces a very large disturbance in the pressure field underneath the airplane, and therefore, there are large variations in static pressure in the streamwise direction. However, the location of the nozzle exit is in an area where the static pressure is relatively close to the freestream static pressure value of 2 psi, for both cases. These preliminary results indicate a well-chosen location for the dual-bell nozzle experiment, with a relatively benign local flow field. It is expected that the inclusion of the ACN stack, as well as the ACN plume, will change the ACN exit pressure. Therefore, preliminary inviscid/Euler CFD solutions were obtained for an F-15 airplane with the full experimental stack. Figures 7(a) and 7(b) illustrate some preliminary CFD predictions for the local flow field underneath an F-15 airplane and the ACN stack with no flow through the ACN. The static pressure contours on the airplane for the Mach 0.9 flight condition are shown in figure 7(a), and the static pressure contours for the Mach 1.2 flight condition are shown in figure 7(b). As expected, the local ACN exit pressures are further below the clean airplane only results that are shown in figure 6. The averaged ACN exit pressure for the transonic flight condition is 1.74 psi, and the supersonic flight condition is 0.98 psi. The supersonic value is only about half of the freestream static pressure, so the stack is producing more disturbance than just the clean airplane. In all cases, the flow streamlines show that the flow remains nice and smooth beneath the airplane, even with the full ACN stack. Figures 8(a) and 8(b) illustrate some preliminary CFD predictions for the local flow field underneath an F-15 airplane and the ACN stack with the nozzle experiment operating. The nozzle total pressure and 6