MASS MODEL OF MICROGASTURBINE SINGLE SPOOL TURBOJET ENGINE

Transcription

1 Journal of KONES Powertrain and Transport, Vol. 0, No MASS MODEL OF MICROGASTURBINE SINGLE SPOOL TURBOJET ENGINE Micha Czarnecki Rzeszow University of Technology Departent of Aircraft and Aircraft Engines Powstaców Warszawy 8, Rzeszow, Poland tel.: , fax: e-ail: czarnecki_@prz.edu.pl Abstract Presented paper consists detailed ass odel of icro gas turbine single spool turbojet in well-known Scheckling design layout (1R/1A). One of ajor criteria in aviation is weight that is granted by airworthiness requireents. At present, exept fro certification process are RC airplanes or UAV with total take-off weight less than.5 kg. Fro the 70's ass odel was added as a part of aero engines design process. Engine weight affects airplane or UAV weight greatly, because it is a source of variety structure loads. Weight reduction efficiency factor, verifying in ters of design quality a icro gas turbine, and the flying object as a syste. Developed coputational odel allows to estiate weight of the coponents (gas generator shaft, copressor rotor, copressor diffuser, cobustor, turbine nozzle, turbine rotor, jet pipe, casings and housings) and whole engine as well. Model inputs are related to technological axisyetric diensions obtained fro thero gas dynaic and construction equations, aking it easy to use. Obtained results was presented for several icro gas turbines (SO1-designed by author, FD3-64, TK-50, JF-50, MW-54, KJ-66, AMT Olypus). Advantage of this odel allows to avoid tie consuing CAD odelling process at design study level. Presented algorith can be used also in the design of UAV as well as issues related to the preliinary ultidisciplinary design and optiization PMDO cases. Keywords: gas turbine, icro gas turbine, turbojet, propulsion, ass odel, Schreckling 1. Introduction Presented coputational odel is based on a prototype icro jet engine SO-1 (Fig. 1). At the stage of the design assuptions entire design work will be siplified but siilar to the coercial gas turbine projects. Model ass as part in the design process of turbine engines was introduced in the 70s of the last century. Weight reduction is one of the quality indicators of the developed solution. In the case of icro gas turbine reduction of engine weight increases the payload efficiency of UAV. It should be noted that airworthiness rules exept for certification process flying aircraft of take-off weight below.5 kg. Mass odel for icro gas turbine turbojet engine was developed for the following siplifying assuptions: - coputational odel corresponds to the 1R-1A design-single stage radial copressor, single stage axial turbine layout (naed Schreckling design fro the author of first successful solution), - engine odel is based on the one-diensional axisyetric cross section cutaway, - input data are characteristic technological diensions.. Mass odel of single spool turbojet The general for of the equation describing the weight of the icro gas turbine engine design coes fro the su of n-ass described by structural units (building blocks e.g. copressor, cobustor, rotor, turbine, jet pipe):

2 M. Czarnecki Fig. 1. Cutaway of SO-1 turbojet engine KONST i 1 n, (1) ass of single structural unit, n nuber of structural unit. Detailed description of icro gas turbine ass equation are shown below: KONST SP OW KS n, () SP copressor, OW rotor case, KS cobustor, TS copressor turbine, DW jet pipe, OB external case. Weight of the copressor unit is described by the relationship: SP SPW SPD SPW copressor rotor, SPD copressor diffuser, SPO copressor case. Weight of copressor rotor is described by equation: TS SPO DW, (3) SPW 0.8DS OB, (3) DS external diension of copressor rotor (Fig. ). This relationship is a reasonable tie saving approxiation for ass estiation and is true for centrifugal design fro kg/s ass flow rate range. Approxiation was verified by data included in the studies of copanies Garrett and Borg Warner [1, 3] and the easureents ade by the author. 50

3 Mass Model of Micro Gas Turbine Single Spool Turbojet Engine Fig.. Basic diensions of SO-1 turbojet engine rotor Weight of the copressor diffuser is described by following equation: SPD D bs ( D4 S b) DLS b ( D3S DS ) sin nldp b bs n diffuser vanes expansion angle (8 14 ), D density of an alloy, bs average wall thickness fro turning process, b height of copressor rotor exit channel (Fig. ), nldp nuber of diffuser vanes (9 14), nlks nuber of cobustor vanes (1 36), D3S external diension of diffuser ain body (Fig. 3), D4S external diension of diffuser (Fig. 3), DLS external diension of copressor rotor bearing. LKS, (5) Fig. 3. Basic diensions of SO-1 turbojet engine non rotating parts Weight of the copressor case is described by equation: SPO 1 D 4S DS D bs 10 b D1 S DS ( DS D3S ), (6)

4 M. Czarnecki D1S copressor inlet internal diension (Fig. 3). Rotor syste and rotor housing weight is described by the relationship: OW OWO OWW. (7) The equation which describes the ass of the rotor housing OWO to fits any design solutions (with tensioner bearing rotor at the rear and at the front of the shaft) [4, 5]. It was assued that the ass of the tunnel shaft is about 10% higher the weight of the sleeve which houses the drive shaft (due the assebling eleents and contact surfaces). Mass of engine rotor housing (tunnel shaft) is described by relationship: OWO 1.1 D bs low DLT, (8) low diension of shaft tunnel (Fig. ), DLT diaeter of turbine bearing (Fig. ). Rotor shaft divided into two parts. First corresponds to the distance between the shaft bearings, second to the length that is necessary to ebedding the copressor rotor and turbine. Adopted ratio is 60/40 []. The design of the rotor shaft is diensioned by internal bearing diaeter DWL. Accepted for technological reasons (the bearing assebly conditions) for the first part of the shaft diaeter of 1.4 DWL. Diensions of the second part will be characterized by the equivalent diaeter of the shaft equal to 0.6 DWL. OWW.04 W low DWL, (9) W density of an shaft alloy. Weight of cobustor is described by following equation: KS gb B 1.17 ( D4S b) ( DLT 3b).36lOW ( b DLT D4S ), (10) B density of an alloy, gb average wall thickness of alloy sheet. Presented relationship is true under the assuption that the axial diension of inner and outer ring is equal to 0.75 low. The distance of the inner ring fro the shaft housing is 3 b (Fig. ) and the outer ring of the otor housing b. The calculations do not take into account the surface of ixing and cooling holes in both rings, as the loss in ass of the rings is copleted by welding binder. Turbine unit weight is described by the relationship: TS, (11) WTS The writing order of coponents in the equation is not accidental because the ass and geoetrical diensions of turbine nozzle is liited by the design of the turbine rotor. Turbine rotor weight is described by relationship: WTS gdts 4 DZ DTS density of an turbine alloy, gdts average thickness of turbine disk, hdts average blade height of turbine disk. DTS ( D zt WDTS D WL ) ( D zt h DTS ), (1) 5

5 Mass Model of Micro Gas Turbine Single Spool Turbojet Engine Mass turbine stator is described by relationship: WDTS gb B 1.57( Dzt DWL) 5 gdts Dzt 1. gdts hwdts nwdts, (13) nwdts nuber of turbine stator blades, hwdts average blade height of turbine stator (nozzle). The weight of jet pipe is described by following equation: Dzt DzD 1.5 ( ) DW gb B ld d zt d zd, (14) ld jet pipe axial diension, dzd jet pipe inner cone exit diaeter. This equation is based on the assuption that the nozzle consists of two truncated cones corresponding to the outer ring and the inner nozzle. Rings weight was increased by 5% due to the connecting ring nozzle to the cobustion chaber and internal ribs that fixes position of inner cone []. Micro gas turbine outer case is described by relationship: OB gb B( D4S low ) 0.5( D4S Dzt ). (15) Presented equation is true for cylindrical case that is adopted for turbine nozzle assebly.. Mass odel verification and suary Nuerical odel was verified on a prototype design []. Real construction weight KONST was kg. Weight of structures calculated on the basis of the present nuerical odel was kg which represents 98% of the real structure. For specific coponents ass calculation nueric odel has a good confority, considering its siplified nature. The largest percentage share in icro gas turbine design eleents had sheet etal structures (outer casing and cobustion chaber Fig. 4). Accordingly, in order to reduce ass of structure designer ust adopt sheet etal with saller thickness also considering the available technologies. Fig. 4. Micro gas turbine coponents weights The coputational odel was verified also for a representative group of icro turbines (Fig. 5). Observed differences are the result of an alternate to start-up systes by air start or electric otor. 53

6 M. Czarnecki Developed odel is a useful tool to optiize the structure ass icro gas turbine jet engine at preliinary study. It also allows to copare the quality of the copetitive structure without using reverse engineering or tie consuing CAD odelling. References Fig. 5. Coparison of real and estiated weights of several icro gas turbine types [1] Borg-Warner, Air Werks, 010. [] Czarnecki, M., Projekt i badania eksperyentalne turbinowego ikrosilnika odrzutowego, Rzeszów 013. [3] Garret, Garret Turbochargers Catalogue, 008. [4] Kaps, T., Model Jet Engines, Traplet Publications, Worcestershire 005. [5] Schreckilng, K., Hoe Built Model Turbines, Traplet Publications, Worcestershire